Berger bullet failure test

I believe the problem is overheating of the jacket and melting of the core is a result of overheating the jacket, as stated above.

The length of the barrel is very likely a big factor but the jacket thickness at the base of the bearing surface is the biggest factor, I believe.

Here is a simple example of frictional heating:

Say one has a cube of copper 0.55"x0.55"x0.55" sitting on a flat steel plate 28 inches long. A pressure of 35000 psi is applied to the top of the cube, thus force between the copper and steel is 10,587.5 pounds force. Say the coefficient of friction between the copper and steel is 0.3, thus if one tried to move the cube horizontally, the force required after the cube began moving would be 3176.25 lbf.

IF the cube were moved 28" then frictional heat would be 3176.25*28/12 ft-lbf or 7411.25 ft-lbf or 9.5 BTU. Thus, the longer the cube is pushed, the more frictional heat is generated which would flow into the cube, the steel plate and the atmosphere.

The coefficient of friction between a bullet and a rifle bore is likely much less than 0.30 because the bore is generally coated with nitrocellulose residue. Through tests I have found that nitrocellulose residue is a great lubricant and many bullets that fragment after being fired out of a dry bore will survive after the bore is fouled.

To reduce bullet failure, the primary concern is increasing the bullet jacket thickness, especially at the base of the bearing surface. That has two effects: If one increases the jacket thickness from 0.020" to 0.025" at the base of the bearing surface, then there is approximately 25% more jacket material to heat up at the hottest part of the jacket. That means the jacket will not be heated as much because there is simply more jacket to heat up. Thus the jacket is stronger because it is cooler and in addition it is further strengthened by the additional thickness.

It appears that making the core of the bullet pure lead has a small advantage in keeping the jacket cooler. The specific heat of lead is higher than antimony and it is likely that the thermal conductivity of pure lead is greater than lead/antimony. Thus the a pure lead core would help slightly in keeping the jacket cooler. In the case of a boat tail bullet, using pure lead would move more of the mass of the core into the boat tail where it can not contribute to dynamic core pressure in the bearing area and thus that would also aid in keeping the jacket cooler. Yet another advantage of pure lead is that it has a higher melting temperature than lead/antimony.

I say a small advantage for pure lead because the specific heat of copper and the thermal conductivity of copper are both substantially greater than lead or antimony. The thermal conductivity of copper is about 19 times greater than the thermal conductivity of pure lead (that is from memory so it is not intended to be an exact ratio).

So again, I believe the primary consideration is increasing the thickness of the jacket in the right places. The jacket is the strength of the bullet and if it is kept relatively cool, the core will not melt whether it is pure lead or lead/antimony.

Eric's comments on the blown primers with the thicker jackets are interesting. Here is the only thing I can think of at the moment: When the primer fires and the propellant begins to burn and drive the bullet into the lead of the rifling, it might be that the thinner jacket deflects inward more than the thicker jacket and is not engraved as deeply, initally, as the heaver jacket is engraved. That would likely result in a higher engraving force for the heavier jacket thus allowing initial pressure to build sooner. That of course is speculation.
 
There has been a lot of information in the last several posts. Instead of discussing specific statements I will share with you my thoughts and knowledge on the general topic which will touch on many of the items dicussed.

The goal is to achieve the higest level of precision while reducing the the number of bullets that fail, it is not to make the toughest bullet. Using alloys that are similar but have more antimony does lower the melting point of lead so this is not better. Alloys including other items like tin are not tested in precision shooting and will require much proving before I'd use these alloys in Bergers.

We did learn long ago that increaing the jacket thickness by 50% (which is much more than we increased the thickness for this test) does not significantly increase the strength of the copper in these thicknesses. Maybe a length of copper that is 12" thick would be much stronger if you made it 18" thick but we are dealing with .001 so this is not the case. The one thing that making the jacket thicker does is it moves the core further away from the source of the heat (friction between the rifling and the bearing surface).

We spent a lot of money and time working with folks at MIT who modeled the stresses that occur when a bullet is moving through the barrel. The result was that while a bullet is solid the greatest stress occurs on the jacket in the area of the ogive near and including the bearing surface (front of the bullet but not the tip).

Once the characteristics of lead as a liquid were used the greatest stress moved to the rear of the bullet and the forces realized by the jacket was tremendously higher than the forces realized by the jacket when the lead was solid. I know this is modeling (not real world testing) and I am not sure exactly what this tells us but it cost us a great deal to learn this so I'd like to believe it is significant:)

I suggest that once the core becomes plastic (not solid) the bullet will fail to some degree. The location of where this bullet will begin to tear apart is frankly not important. I accept that the suggestion of shooting bullets in a twist that is too slow will allow for us to see where that particular bullet starts to tear appart but I will suggest that a bullet that is tumbling is realizing extreme forces similar to those realized by shooting point forward through a board.

My point here is that both testing methods are flawed because neither duplicates what a bullet experiences in typical flight. The only way to see for sure where a bullet begins to tear apart in typical flight is with the high speed video which is horribly expensive and can only record inches of the bullets flight path. (This technology is available for about $350,000 from a vendor we spent a lot of time talking to at the SHOT Show.

Focussing on where the bullet starts to tear apart is like trying to analyse where would be the best place to stick your finger if a dam sprung a leak. Instead the focus should be directed to the only area of the bullet that matters in this situation and that is where the heat is realized because this is what creates the condition that tears the bullet apart.

I believe strongly that heat is what makes a bullet fail. I also believe strongly that heat may produce poor accuracy (fliers). I further believe that there are many ways to manage heat since heat in this case is the direct result of friction.

Anyone who is looking at the burning powder or the friction realized by the air is wasting their time and efforts. The greatest source of heat on a bullet is the friction at the point where the rifling engages the bearing surface.

I will agree that the heat may be greatest (in this area) toward the rear of the bearing surface (although this is speculation on my part). I will also share that I strongly believe that the heat is the highest on the bullet at the muzzle.

Anything that can be done to address this heat is a step in the right direction. Land configuration, bore diameter, groove diameter, barrel surface finished, the characteristics of the copper, lubricant on the bullet, lubricant applied to the barrel, inclusions, metal stresses, carbon or copper fouling, cleaning practices and solvents used, lead angle and roughness (from reamers that are not sharp), load pressures and the resulting velocity, barrel length, barrel blocks instead of action blocks on BR rail guns and finally the bullets (jacket thickness, bearing surface length, OD, lead hardness, bullet straightness). All of these things (and probably a few others I didn't think of) influence the heat realized by the bullet.

As a bullet maker I can only influence my product. I can apply solutions to the bullet that either reduce friction or increase the bullets ability to absorb (withstand may be a better word) heat while protecting the core (and overall structure of the bullet) so that the bullet hits where you aimed it. Because this is important I will continue to pursue this course and our next step is the introduction of a full line of THICK jacketed bullets.

Frankly, there are many shooters who won't need these thick jacketed bullets because they manage or address the other causes of heat. For those who either want to push the limits of their equipment or for those who just don't want to worry about it (and likely take no specific steps to address heat) they will now have an option.

Someone will find a way to make these thicker jacketed bullets fail. I will admit that I don't know how hard I will work to solve that issue since it is likely that this person is pushing the extremes even farther than is safe or reasonable. I will, however, solve our part of this issue so that I don't have to hear the "J4s are too thin" statement ever again.

Regards,
Eric
 
Two more quick statements:

1. I agree with Henry's description of how the heat moves through copper of different thicknesses (mass). I have been talking from the point of view that the thicker jacket insulates the lead core from the heat. It is more likely that the thicker jacket reacts to the heat as Henry describes which results in preventing the core from realizing tempurates high enough to melt. You might say that we are saying the same thing differently but I feel clarity is key to applying successful solutions.

2. The jackets that Randy mentioned that were aquired through Bill Niemi were J4 jackets. They were 25 cal jackets that were sized down to 6mm. The 25 cal jacket is made with .032 base thickness material. Standard 6mm J4 jackets are made with .027 base thickness material.

Using 25 cal jackets to make 6mm jackets will produce a 6mm jacket that is thicker than regular 6mm jackets. This solved the failure issue in this case. The THICK jackets that we produced for our test were made with the same base thickness material that is use in our standard 6.5mm jackets. The portion of the jacket that is thicker is in specific locations up the side wall.

Regards,
Eric
 
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Coated bullets

I was really surprised by the failures of the molied bullets as it's been a very successful solution to one of your competitors bullets that was blowing up on me. Since I started coating (maybe 500 rounds ago) I haven't had a single failure. I know this isn't what this test is all about, just related. I hope you can do a little test of some sort, on it's own with appropriate methods and controls. Like doing the moly test 1st before the barrels are scorched. Coating bullets and and handling them is undesireable, but effective in my application and experience. And technically, I use Danzac.
 
Kabang,

I believe strongly that dry lubricant on the bullets does help with the bullet failure situation. I also believe strongly that these lubricants help maintain precision for longer periods during a particular shooting session. Walt, Eunice (while she was alive) and I have shot nothing but moly coated bullets since moly was introduced.

Shooting moly during this particular test was not meant to prove or disprove anything about moly. The barrels had been thoroughly abused with many rounds shot very rapidly with minimal cleaning. I did not believe that moly by itself at the end of this particular type of shooting was going to prevent failures.

The funny thing about testing is that it is always better to guess and prove with a test than it is to guess and have nothing to back it up. Many folks guessed that the Patriots were going to win the Super Bowl. They played the game for a reason and we shot moly after this test out of curiosity.

A thorough testing of coating and its influences on bullet failures will require many barrels and tightly controlled processes. Several barrels would be required to confirm truly consistent and repeatable result. It is possible to do this but would be more than most are capable of doing.

Looking at the fact that moly does reduce velocity because of reduced pressures I am compelled to believe than this reduced pressure comes from reduced friction. Anything that reduces friction helps reduce or eliminate bullet failures.

For the record I talk more about moly because it is what I have used. I am sure that danzac, boron or any other true lubricant bullet coating will influence bullet failure by reducing friction. I have no proof of any of this but it makes sense to me.

Regards,
Eric
 
Eric Stecker said:
T
The location of where this bullet will begin to tear apart is frankly not important.

The above statement, by Eric, is selfdefeating in the goal to design a better match bullet. The point at which the bullet fails is extremely important and can confirm what is causing the bullet failure or give one a clue as to what the cause of failure is.

The point of failure, for a bullet failing due to an overheated jacket, will be found to be at or very near the base of the bearing surface and that is the area the jacket must be made thicker. That heating is the result of jacket to bore friction, partially from static forces of forcing the bullet through a bore in which it will not freely fit. But the primary frictional forces are due to dynamic core pressure which increases from near zero at the top of the lead core to approximately 35,000 psi, at maximum chamber pressure, at the base of the bearing surface. You might not understand the concept but the folks at MIT who did work for you will understand that concept. Henry

I accept that the suggestion of shooting bullets in a twist that is too slow will allow for us to see where that particular bullet starts to tear appart but I will suggest that a bullet that is tumbling is realizing extreme forces similar to those realized by shooting point forward through a board. (Eric)


Your comments in the paragraph above are not correct. The primary stress producing force on the bullet as it exits the muzzle of the rifle from a maximum charge of a long range match load is the base pressure which induces core pressure and resulting tensile stress in the jacket.

The next significant stress producing force is centrifugal force resulting from the high rotational speed of the bullet imparted by the 8" to 9" twist rifling used in the tests described above. Shooting a 121 grain 6mm Bib bullet out of a 12" twist will not introduce additional significant stresses in the bullet. The reason is that the tumbling rate of the bullet is extremely slow compared to the rotational speed imparted by the rifling. Since centrifugal force varies with the square of the rotational speed, the centrifugal forces resulting from the bullet tumbling would be vanishingly small. Henry

(all comments below by Henry)

Core melting: If one analyzes the heat required to melt the entire core of a Berger 6.5 mm, 140 grain VLD bullet (a one sample core weight of 99.29 grains) then one will realize that only part of the core melts when the jacket gets too hot. It is not possible to melt the entire core when the bullet is fired normally with an acceptable load.

The above statement is not that significant but just a point of information. What is important though is that if any part of the core melts then the jacket has likely gotten too hot and will be more likely to fail.

Copper has one of the highest coefficients of thermal conductivity of all pure metals (only silver and gold have higher values), about 11 times greater than pure lead. But in order to melt part of the lead core in only 1.5 miliseconds the temperture drop across the jacket is very large (heat flow = conductivity coefficient X temperature difference X area). The inside surface of the jacket must be much greater than the melting temperature of the core in order for the high heat transfer rate to take place. That means that when part of the core melts, the exterior surface of the jacket is likely as hot as 1000F or higher. That weakens the jacket and increases the likelhood of jacket failure.

One does not want to insulate the core from heat flow but wants to send as much heat flow to the core as possible without getting the jacket too hot. That is why using pure lead will help. Pure lead likely has a higher heat transfer coefficient than lead/antimony or lead/tin.

Coefficient of thermal conductance is the heat flow a material will pass through a unit thickness, through a normal unit area for one unit of temperature difference.

The coefficient of thermal conductance of pure copper is:
11.3 times greater than pure lead
18.8 times greater than pure antimony
5.9 times greater than pure tin

Heat capacity is the amount of heat required to heat a unit mass of material one unit degree of temperature:

The heat capacity of pure copper is:
3 times greater than pure lead
1.9 times greater than pure antimony
1.7 times greater than pure tin

Heat capacity, like thermal conductance, is very important in transient heat transfer (Heat flow to a bullet as it travels down a barrel of a rifle is an extreme case of transient heat flow.). In the example of copper and lead it means that the temperature of one pound of copper will heat up 1/3 rd. the temperture rise of one pound of lead when absorbing the same amount of heat.

The above values are for pure materials but in the final analysis, in comparing pure lead to lead/antimony, the thermal conductivity of lead/antimony must be known.

However, I believe the most importan improvement that can be made in match bullet jackets is to increase the jacket thickness where the the jacket gets hottest over the greatest time period. A thicker jacket will absorb more heat and it will provide a larger channel area to conduct heat to other parts of the jacket.

It might be true that the hottest point on the bullet jacket occurs while the bullet is forced into the rifling lead. But keep that in perspective: 1) the area of engagement of the rifling lead is small and 2) the time period of engagement is only about 1% of the bullet travel time in the barrel.

You might not understand it but again, your friends at MIT will, after the jacket engages the rifling lead, the area of highest friction and jacket heating due to friction is at the rear of the bearing area and that remains true for approximately 99% of the bullet's travel through the barrel.

Henry
Click to expand...
 
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great to see ya back online henry

is it possible to calculate the reduction of friction by reduction of duration or barrel length?i have noticed that most reported falures have come out of 29-30 inch barrels,if the bullet destroying barrels were shortend by 1 inch at a time to the point of not destroying,would that produce a valid result with your theory of jacket heating ? tim in tx
 
Henry,

I do not wish to engage you in a pissing match since you are obviously much stronger in mechanical engineering knowledge. Your theoretical (based on facts you know along with few others) analysis cannot be disputed directly by me. I have read your entire post and it seems that you have reached the same solution that we have so I am not sure what is the goal of your post.

Is there really a reason to debate the significance of one method of determining the result over another. You are assuming that the point where the jacket tears apart is also the point where the cause of the tear occurs. Having seen Dave Tooley testing where he marks the bullet with a sharpie it has been proven that the jacket tears in random places around the bullet not in relation to any given point in the barrel.

This being true (and proven) it is reasonable that the location of the tearing of the jacket is not directly connected to the true root cause which is heat caused by friction between the rifling and the bearing surface. Dave Tooley's testing on this subject was a significant discovery because it allowed us to shift our focus from the result to the cause. It seems to me that looking at the result now is the same as trying to figure out how a drunk driver got into an accident by looking at the site of the crash. In this example the drink is what caused the crash and the solution to preventing the crash is found there not at the crash site.

Your following statement:

"It might be true that the hottest point on the bullet jacket occurs while the bullet is forced into the rifling lead. But keep that in perspective: 1) the area of engagement of the rifling lead is small and 2) the time period of engagement is only about 1% of the bullet travel time in the barrel."

This statement tells me that you have not been internalizing my information but have actually been focusing on how you can dispute it. I have said many times that the greatest source of heat is the friction between the rifling and the bearing surface. This has been proven (beyond all doubt) in high speed thermal images.

I mentioned lead angle along with a long list of items that should be a part of a shooters understand of all of the things that MAY influence the friction realized between the rifling and the bearing surface. These statement are focused on providing shooters ways to manage friction which is the solution rather than being meant to focus on the result.

Henry, just because I cannot quote the coefficient of thermal conductance of pure copper or because I do not have the years of training in mechanical engineering does not mean that I cannot understand or analyze facts presented in a way that leads to a solution. Your shots at my intellect are again focused on your means to dispute our findings rather that to embrace our solution.

Our solution has been proven to work. We will be implementing our solution in a full line of THICK bullets. I am confident that this solution will solve the problem. Your vast experience and understanding of mechanical engineering had not provided you with a solution that was found to be successful and in fact you are the one who was originally pushing the "lead too high in the ogive causes failures" theory which has been proven to be false.

I will suggest that you offer your opinions as "your OPINIONS" and that you not provide such strong support of them until they are proven. Many people read these posts and you sound like an expert. I am not saying that you are not knowledgeable but some of your statements do not jive with facts proven in real world testing.

Believe me when I say that I respect your knowledge. I am listening to your comments and I am internalizing the role they play in the solution. Please do not be so prideful in your opinions that you cannot accept that someone like me who "doesn't understand" may in fact be capable of finding and implementing the solution.

Regards,
Eric
 
bullet blowup

Eric:

Just my $.02: (1) I am very glad that you and Berger Bullets continue this open forum to the benefit of competitive shooters on such a "hot" topic; (2) It is great to see Henry Childs back posting on this board as his reputation is top shelf; (3) Randy's imput is invaluable (4) I would also love to see Bryan Litz (sp) and Charles Ellertson engaged in this thread as well.

I have blown up four bullets in my competitive shooting, all at Hawks Ridge on the same relay. I was shooting a 300 WSM with N560 pushing 187 BIBs out of a 12 twist. I blew up 3 on my sighters and one during a record light gun string (5 shots). The shots on paper were nicely formed in about a 5" group.

That evening I loaded the same brass with the same lot of bullets -- but with a somewhat compressed charge of H-1000. On the next day, I experienced no blowups and I won my relay with somewhere around a 5" group.

Of course, an additional variable on this occasion was that the H-1000 load was considerably under the fps of the N560 load. I never really figured it out as I have shot a lot of N560 before and after the blowups, with the same barrel and lot of bullets with no problems.

FWIW, I have noticed that I can actually "feel" the difference in barrel heat after a string with N560 as compared to H-1000, H4831SC, H4350 etc., and I can also feel the difference in barrel heat when shooting moly vs. naked bullets. I suspect that one is related to the double base powder and the other is a coefficent of friction issue.

Keep up the good work as this is a very educational thread.

Jim
 
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eric i have a large number of years in QA, don't want to tell how many cause i'm old. oh well you are going about this in a different manner than i would but you appear to be well on your way to getting to the answer. from all of the posts i believe that you are going in the right direction with the jacket thickness. if the jackets are failing then increasing there ability to hold together is a logical solution. it really matters not weather the temp or the type of rifling is the problem. if it doesn't work then you know one thing more than when you started and can try something else. i shoot your .224 75 gr vld from a kreiger cut barrel, i have had none of the problems listed in this post. i have found that shooting them at less than the ragged edge of the velocity envelope get me better groups. what you do with j-4 jackets is a marvel. i did find that i was getting more flyer's if i didn't lube the case necks when loading them but that was my problem and not the bullet. happy hunting you have an elusive pray in mind.
 
Some perspective

I've got no intention of 'mixing it up' on any of the technical issues discussed on this thread, but I would like to comment on the relevance, scope and implications of solving the bullet failure problem.

Successful long range shooting is most easily achieved by pushing the highest BC bullet to the highest possible velocity while maintaining precision. Historically, bullet failure has been one of the key problems in achieving greater speeds with high BC bullets, especially in smaller calibers. Solving the failure problem raises the collective bar in long range shooting. However, bullet failure isn't the only problem. Other limiting factors are barrel life and more energetic (and safe) powder formulations. What I'm saying is:

Advancing the technology of LR shooting is done by improving the entire system, one piece at a time.

Dwelling on the details of why one explanation of bullet failure is or isn't precisely accurate doesn't interest me. It's been demonstrated by extensive and credible testing that thicker jackets solved the problem (or at least drastically increase the thresh-hold). OK, we've got it. What's the next problem?

Eric indicated that the thicker jackets increased pressures, enough to blow primers. This could be the next problem to solve. Perhaps the thicker jackets will require a slower burning powder than what's typically used in the popular 6.5-284 cartridge. Maybe the slower burning powder, combined with more survivable bullets will result in a combination superior to (faster than) anything the 6.5-.284 could do before.

Beyond the powder and bullet problem is the barrel wear gremlin. What options do we have for making longer lasting throats? Ceramics? Who knows.

My point is that a long range rifle is a system. To improve a system, you have to strengthen the weakest link in the chain, and insure all the parts work together well. It used to be (in some cases) that bullet failure was the weakest link in the chain. Thanks to the testing that Eric reported on, this is no longer the case. We can now move on to the next problem, the next 'weakest link'.

It's ironic from a historical point of view, that an improvement to bullet technology (more survivable jackets) may drive advancement in propellant technology. If I remember correctly, it was the advent of smokeless powder, and the high performance associated with it that caused bullets to require jackets in the first place. Will the chemists at Hogdens, Vita Vouri, or IMR even attempt to 'step up' and engage? The ball may be in their court now. If there is something that prevents them making better propellant, we should at least understand the limitations.

I think Eric and Berger bullets is doing their part to advance the shooting sports by solving problems which will elevate the reliability of our projectiles at higher speeds. If further improvement of the 'shooting system' is to occur, it will have to be done by improving other parts of the system. I'm not saying that bullets are as good as they'll ever be, I'm just saying they're not the weakest link anymore.

When Eric comes on these forums and shares results with us like he does, we should be supportive and grateful (as some of us are) that someone in the industry actually cares about making things better instead of arguing over the details. Of course it's acceptable, even encouraged to challenge ideas put forth on the forums. But when someone comes thru with a tested and proven solution, there's nothing to argue. As far as I'm concerned, we should simply say 'thank you', and go about attacking the next weakest link.

-Bryan
 
Eric,

I don't have it in for you. I have truly been trying to help.

I came back into BRC through a link sent to me by Lynn Dragoman and that is the only reason I was aware of this discussion. It is good to see you are making progress on improving your bullets. Good luck.

Henry
 
Lynn,

I appreciate your post. I do not have a bad opinion of Henry. We have disagreed before and likely will again down the road. I do not take these debates personally.

I believe these exchanges help us all learn. Without Henry questioning the height of the lead in the nose we would not have considered it. Turns out it doesn't cause failure but what if it did? He shined a light on an area that was not previously considered.

I have spent many years listening to everything. Just because I don't agree does not mean I do not take serious information seriously. I would be a fool not to. I look forward to more of Henry's thoughts along with the many others who engage these forums with a genuine desire to obtain and share knowledge.

Regards,
Eric
 
Back woods perspective.

I appreciate this thread and the contributers .
I have been doing my own thing quietly on my own , with moly coating and bullet swaging for a very long time.
Lot of fancy words spoken and technical stuff talked about here. Truth is it is giving me a headache .
I learnt a long time ago that a rough barrel can blow up a light jacket.
Cut rifle barrels can be very accurate but can also put too deep engraving on the bullet .
Bullets do overheat and blow up and it is the jacket that explodes from getting too weak to contain the cetrifugal force from the rotation.
However their is many different bullet designs , a jacket that is hollow at the base and exposing the core may act differently. A meplat may open a bit inducing a sudden increase in drag which will have a domino effect and explode the bullet just the same as hitting a hard target. The Ogive could bulge and fail causing a similar result.
I believe that a quality coating of Moly Disulphide can help if the problem is marginal. If the problem is severe as in Bergers purposefull test conditions , then it will not stop it as far as I have observed .
Because I coated some bullets for a friend that was having these same problems and it only improved it somewhat .
In the end we lapped the barrel and dropped the velocity and with the coating it stopped the problem with those bullets anyway.
I think that only indepth testing by a big organization like Berger , Sierra or Norma can really come up with exact reliable data in the long run.
However I have never relied on the industry to tell me what is going on because sometimes they will keep it to themselves , its that competitive edge thing.
 
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Fascinating post from one and all.
Made me register with this forum.
Sorry if I have missed this but two questions occur to me:-

1. If the core weight was the same presumably the overall bullet weight of the thicker jacketed bullets was heavier? It would be interesting to reduce the core weight to give the same overall weight (probably what you have done in the production bullets) to see if the pressure effect is indeed jacket thickness related or simply bullet weight related.

2. It would be interesting to know the distance the test was done at? Some of the blowups I have heard of have been well down range so testing at short range does not guarantee performance at long. Unless someone has data I would not rule out bullets warming due to air resistance. A back of envelope calc shows that if all the bullet's kinetic energy were turned to bullet heat the temperature rise would be a couple of thousand degrees. Fortunately for the bullet most of the energy will go to noise and warming the air but bullets do land very hot. At 1k I have seen a marker trying to pick up a ricochet which landed on the butt floor but dropped it saying "ouch" as it was still so hot. Even if the bullets do not gain heat outside the barrel the heat may still be spreading from jacket to core which will affect matters downrange.

Mike
 
mikebbh said:
Fascinating post from one and all.
Made me register with this forum.
Sorry if I have missed this but two questions occur to me:-

1. If the core weight was the same presumably the overall bullet weight of the thicker jacketed bullets was heavier? It would be interesting to reduce the core weight to give the same overall weight (probably what you have done in the production bullets) to see if the pressure effect is indeed jacket thickness related or simply bullet weight related.

2. It would be interesting to know the distance the test was done at? Some of the blowups I have heard of have been well down range so testing at short range does not guarantee performance at long. Unless someone has data I would not rule out bullets warming due to air resistance. A back of envelope calc shows that if all the bullet's kinetic energy were turned to bullet heat the temperature rise would be a couple of thousand degrees.
Fortunately for the bullet most of the energy will go to noise and warming the air but bullets do land very hot. At 1k I have seen a marker trying to pick up a ricochet which landed on the butt floor but dropped it saying "ouch" as it was still so hot. Even if the bullets do not gain heat outside the barrel the heat may still be spreading from jacket to core which will affect matters downrange.

Mike
Click to expand...



Mike has raised an interesting point....if the jacket is thicker it should mean less lead in the core. How is the bullet weight maintained? Is the bullet longer or is the ogive moved towards the tip.

Also as a target shooter I now have regular Berger 6mm 108 BT and a couple of boxes of 6mm 108 THICK. I would assume that they should be no difference in accuracy between the two different jacket thicknesses?
 
I am fairly certain that bullets get hot from air friction also so if the bullet is over heated in a rough barrel and subjected to deep engraving from a particular design rifling in combination with a thin jacket and quick firing that over heats the barrel , then a blow up can occur close or down range depending on many initial heating factors , bullet velocity and construction.
I am fairly sure that the vapour trail that you can sometimes see in the air with the naked eye and especially in slow motion photography , is in part moisture being boiled by the bullet to air friction.
As the jacket gets thicker there is less space inside for the core.
There is few ways they could adjust the thicker jacket bullet to a specific weight. Use a longer jacket with the same ogive and get extra weight in the longer shank .
If there is extra space inside the original meplat ( core depth ) then just add extra core weight and have the ogive fill out more ( less core depth )
Use the same length jacket and core depth but use a blunter ogive that holds more weight . Reduce the angle of any boat tail so it holds more weight without increasing length .
 
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Mikebbh,

By making the jacket thicker we are moving the lead away from the greatest source of heat which is the rifling. The change in thickness is not great enough and in locations that would result in a considerable increase in the jacket weight. We do need slightly less lead since the jacket is heavier and we maintain end weight consistency (140 gr for example). However, lead being more dense means that proportionally we add more copper than the amount of lead we remove which results in a slight increase in the amount of lead in the nose. The difference is real but slight.

We shot the bullets into the berm at Ben Avery Range in Phoenix from the 1,000 yard firing line. 2 and 3 folks with scopes observed each shot (besides the shooter). All of those who observed the shooting agree that the failures (blowups) occured at various distances. Some seemed to blow up immediately out of the barrel (accompanied by an unusual crack sound) while others produced vapor trails for a considerable distance but did not impact the berm.

Bushpilotmexico,

The weight of these bullets was 140 gr (with +/- weight variation consistent with a normal bullet run). The outside dimensions were exactly the same as our standard jacketed bullets as both these batches were run on exactly the same set up. No adjustments were made other than the use of a smaller seater punch.

You are correct in your belief that the accuracy will be no different between the standard and thick 6mm 108 gr BT. The thicker jacket is meant only to ensure that you do not realize failures. Everything else is the same.

There is one potential upside that might come from the thicker jacket. Our testing and focus has been on catostrophic bullet failures. These are bullets that do not make it to the target. We know that the lead melt and that once it does no jacket can take the pressure from a material as dense as lead spinning freely as a liquid at 250,000 RPMs. The key to our solution is to keep the core from melting in the first place. But what about the bullet that has only a slight softening of the core material.

Could a core melt slightly enough that the bullet could hit the target but not where you thought it would? I believe the answer to this question is yes it can. The thicker jacket could both eliminate catostrophic failure and help reduce or eliminate some of the unexplained flyers especially those that occur when you were pouring the other shots one on top of the other. We'll have to wait and see.

Regards,
Eric
 
Eric Stecker said:
Bushpilotmexico,

The weight of these bullets was 140 gr (with +/- weight variation consistent with a normal bullet run). The outside dimensions were exactly the same as our standard jacketed bullets as both these batches were run on exactly the same set up. No adjustments were made other than the use of a smaller seater punch.

You are correct in your belief that the accuracy will be no different between the standard and thick 6mm 108 gr BT. The thicker jacket is meant only to ensure that you do not realize failures. Everything else is the same.

There is one potential upside that might come from the thicker jacket. Our testing and focus has been on catostrophic bullet failures. These are bullets that do not make it to the target. We know that the lead melt and that once it does no jacket can take the pressure from a material as dense as lead spinning freely as a liquid at 250,000 RPMs. The key to our solution is to keep the core from melting in the first place. But what about the bullet that has only a slight softening of the core material.

Could a core melt slightly enough that the bullet could hit the target but not where you thought it would? I believe the answer to this question is yes it can. The thicker jacket could both eliminate catostrophic failure and help reduce or eliminate some of the unexplained flyers especially those that occur when you were pouring the other shots one on top of the other. We'll have to wait and see.

Regards,
Eric
Click to expand...


Hi Eric,

You've perked my curiosity, I'm shooting a 6BR using your 108 BT bullets out of a 28" Krieger barrel 1 in 8 twist at a muzzle velocity of 2980 fps. From your experience what are the chances of the lead core actually melting at 100 yards out to 1000 yards at that velocity and twist?

My friend was fortunate enough to get 2 boxes of your 108 THICK and at 100 yards in his Krieger 6BR is almost putting them in the same hole with no flyers at 300 yards he is getting less than 3/4" groups. Your theory about the molten core and the possible flyers is interesting but if the core was molten and the jacket holds together would accuracy suffer? Any flyer I have seen still seems to punch a clean hole.
 
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