Berger bullet failure test

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Eric Stecker

New member
First I want to thank Mid Tompkins for doing so much to make this test possible. Without him it would not have happened. Also I want to thank Sherri Hurd and Michelle Gallagher for their part in putting 950 shots down range using a 6.5X284 in a little over 6 hours. You both earned those sore shoulders.

On January 3rd at Ben Avery Shooting Facility in Phoenix, AZ we (in my opinion) solved the bullet failure issue. We conducted a test during which 220 Berger 6.5mm 140 gr VLD made with regular J4 jackets were fired in two different barrels. After these rounds were fired we shot another 220 rounds of Berger 6.5mm 140 gr VLD made with thicker J4 jackets. The results were interesting to say the least.

Two barrels that had been provided by Krieger were chambered by Mid Tompkins. These barrels were put on two F-Class rifles (Mid's and Bob Mead's). A front rest, rear bag and shooting mat were used in shooting these rifles F-Class style.

Mid and Michelle spent much of the holidays loading the 950 rounds shot during this test. The ammo was loaded in Lapua cases with 49.5 gr of H4350.

Present during the test were Mid Tompkins, Michelle Gallagher, Sherri Hurd, Jeremy Hurd, Bob Jones, Alan Elliot, Walt Berger and I. We made sure that for each shot there were at least two people watching through spotting scopes. All shots were documented.

The goal was to shoot all the rounds in highly abusive conditions and then observe if the bullets would fail. We did not alter the barrels or the load in an attempt to create failures on purpose. These barrels and loads were in every way in the same condition when we started as any combination would be on match day.

The procedure used for this test was to fire 20 rounds with one rifle then quickly switch to the other rifle. We would shoot all 220 (in each barrel) of the regular jacket bullets first then shoot all 220 of the thicker jackets. This course of fire was meant to duplicate match type strings and the rapid firing was to produce the harshest conditions possible for the bullets.

As you can imagine the barrels were very hot to the touch once we got through the first few strings of 20 shots. They would remain hot for the rest of the day.

We started with the .257 barrel first. We were not testing barrels so observations made about the barrels are secondary to the focus of the test. I mention this because I predicted that the .257 bore diameter would produce fewer failures since it was larger than the .256 bore diameter. I was proven wrong.

The .257 bore diameter barrel produced the first bullet failure at shot 106. The .256 bore diameter barrel produced its first bullet failure at shot 151. Even more interesting was the fact that the .257 barrel produced a total of 27 failures (with regular jacket bullets) right up to the last shot. The .256 barrel produced only 12 failures and stopped producing failures when the barrel was cleaned after shot 180. 40 shots were fired after both barrels were cleaned.

Now for the good news. After we finished shooting the bullets made with regular jackets we switched to the thicker jackets. Again both barrels shot 220 each by shooting a string of 20 and then switching to the other rifle. ALL 220 BULLETS MADE WITH THICKER J4 JACKETS (IN BOTH BARRELS) MADE IT TO THE IMPACT BERM.

So that we did not destroy one of Mid's target frames the scopes were adjusted so that we could aim on a target but the bullets would hit the impact area of the next target. At the beginning of the thick jacket shooting we did shoot one 10 shot string on the target. The results were a 12 oclock 6 due to scope adjustment, 8-Xs and 1-10 (string shot by Michelle G.) Accuracy was not the focus of this test but it looked good for ten shots (once we got the scope adjusted).

To verify that something had not changed in the barrel for the thicker bullets we shot another 20 bullets made on the regular jackets in the .257 barrel after the thicker jacket shooting was completed. 9 out of 20 shots fired did not make it to the berm.

Another interesting result was that while we were shooting the thicker jacketed bullets both barrels produced several blown primers. The .257 barrel produced 14 blown primers and the .256 barrel produced 5. There were no blown primers while shooting the regular jacket bullets. We did chronograph five shots using regular bullets at a MV range of 2,996 to 3,024 fps. The chronograph was not working later in the day so we could not check the MV produced when shooting the thicker jacket bullets.

We continued shooting after thoroughly cleaning the .257 barrel using moly coated bullets made with regular jackets. 50 rounds were fired with 14 failures. It is my opinion that the abuse this barrel had experienced does not allow for an appropriate testing of the effectiveness of moly. These bullets were shot mostly out of curiosity. It is certainly clear that moly is not a cure all for bullet failure however I still believe that it helps reduce friction which is the cause of these bullet failures.

It is my conclusion that bullets made with thicker jackets are more capable of sustaining significantly higher levels of abuse before producing a failure. We are gong to do this same test again but this time we will use Bartlein barrels. The purpose again is not to test the barrels but to focus on the results produced by using jackets of different thicknesses.

Even though we are going to conduct another test we are already working on the production of a full line of VLD-THICK bullets in 6.5mm, 6mm, 22 cal and 7mm which will be specifically meant for target competition shooters. I will attempt to attach a detailed report of the specifics of the test.

Regards,
Eric
 

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Eric,

Those results are very convincing. Can I ask the question that everyone will be asking please? What is your expected timeline for production of the "VLD thick" range?

Also, what was the concensus on the reason for blown primers with the thicker jackets - was it thicker jacket = greater friction = higher pressure?

Thank you for sharing this information with your customers. Your credibility will skyrocket if you continue with this level of transparency.

Alan
 
Very Interesting results

Eric et al:

Thank you for sharing your information. I had an interesting conversation last year with Bill Hobert of Swift Bullet company last year at the Shot Show. He said they had to change the jacket alloy for bullets smaller than 7mm due to bullet failures. They had to go to a more ductile mixture to produce the 6.5, 6mm, and 22 caliber Scirocco IIs. They were worried about copper fouling but the testing results were so good that they switched to the softer alloy in the 7mm, and 30 calibers. Have you considered a softer alloy and bonding the jacket to the core?
Nat Lambeth
 
Alan,

Regarding the availability of our THICK J4 jacketed bullets I can tell you that we are moving things forward as quickly as we can (how is that for a non-commital answer). The modifications to the tooling and additional tooling are not massive but we are finding several unexpected steps needed in tooling up for the THICK line. I can assure you and everyone that this is a high priority and we will be announcing when the bullets hit the shelves.

Regarding the blown primers, I can share that the only difference in the ammo was the thicker jacket on the bullet. This compels us to conclude that the thicker jacket must have influenced pressure. The lack of a working chronograph (at this stage of the test) did not allow us to confirm at least that the velocity had changed. The truth is that I don't know for certain why the primers blew. I am looking forward to repeating this test to see if the blown primer result happens again.

Thank you for your kind words. I am geninely interested in the growth and strengthening of the shooting sports. I will do everything I can to enhance the shooting experience.

Regards,
Eric
 
Nat,

To best answer your question I must share something that many may already know. I am commited to the belief that Walt developed the best method for making bullets with the highest possible precision capability. Because I feel strongly about this I will go to great lengths to avoid changing the way we make bullets.

Through the 90's we spent 5 years trying to build a "hunting" bullet. One of the requirements was that this hunting bullet must be capable of 1/4 minute accuracy out of a good rifle. We tried bonding, different metals and alloys, mechanical locks, small jackets inside large jackets and different hardnesses. We annealled, hardened, melted, froze and applied every influence to the various metals we could think of to achieve our goal. The bottom line is that nothing we tried met our accuracy requirement (weight retention and penetration goals were met but we know now that these goals are of little importance for a good hunting bullet).

We spent an incredible amount of time, energy and funds trying to figure out the true root cause for bullet failure so that we could apply a change that would be sure to work. Many have been frustrated that we have taken so long to resolve this problem. The reason for the lengthy delay is that I will not change what is not broken unless I have indisputable and recreatable evidence that it will be a real solution and will not reduce the precision capability of our bullets.

This is a long answer to your question but I wanted to take advantage of the opportunity to share my core beliefs about bullet making since they apply to your question.

Regards,
Eric
 
bullet blowup

Eric:

Your work is appreciated. I (and I suspect others) would like to know how button barrels (like a 5C Broughton, Lilja or Hart) would fair in the test compared to the two brands of cut barrels you are using in the tests.

Of course, this would open the door to any differences between conventional button rifleing and canted lands, the number of groves, etc, etc.

I know you can only test one thing at a time, but a button barrel on your next test MIGHT tell us more than another cut barrel.

Again, thanks for all your work, and just consider this food for thought -- in your "spare" time. :)

Jim Hardy
 
Jim,

I appreciate your point and we may continue our testing beyond cut barrels for the sake of observation. It is important to note that our focus was to solve a bullet issue. We used the Krieger 30" barrel because this is the barrel mentioned in most bullet failure reports.

Krieger sells A LOT of barrels to long range target shooters so the high level of reports can be simply a representation of how many folks are using Krieger. It is also important to mention that Krieger was completely supportive of our testing and desire to pursue a solution to this bullet issue.

Having said that it has been proven that the hottest part of the bullet is where the rifling engages the bearing surface. There has been no testing on this subject however it seems logical that changes in the land configurations would affect the amount of friction (heat) realized by bullet.

We plan on using the Bartlien barrels in the next test primarily because we are still testing bullets and Bartliens are dimensionally similar to Kriegers. It makes sense to use a cut rifle for this test to make as close of an apples to apples comparison of the bullets results.

Regards,
Eric
 
What's the basis for FRICTION as the cause of failure?
Why do your bullets fail? Because their jackets aren't thick enough?
Are the cores too high in the nose?

What was the twist of these barrels?

Thanks
 
Mike,

I am going to respond to your questions so that others who are reading this forum may learn what you seem to be unable to internalize.

Failures have several causes. The most common is produced by the core melting. The core melts because it gets too hot. The core gets too hot because of the FRICTION between the rifling and bearing surface. This has been proven to be the hottest part of the bullet as it moves through the barrel. This area has been shown in high speed, infared images reaching tempuratures at the melting point of lead.

Other causes for failure are excessive RPM. Since most shooters use factory (bullet or barrel) recommended twist rates failures due to excessive twist rates are rare (but do happen).

Rarer still is a failure caused by extreme barrel issues (damaged bore) extremely poor loading practices (damaged bullet) or extremely poor cleaning practices (which further increases friction).

Another extremely rare cause is related to bullet production issues. Bullet construction that is poor enough to result in bullet failure (and where bullet failure would not have occurred for any other reason) can theoretically occur in situations where standard QA and production procedures are ignored almost completely. I am sure that this is possible but is as unlikely as I can imagine (from all bullet makers).

These reasons for failure are true for all bullets. Bullets from every maker can experience failure under the right (or wrong) conditions. Recently, Sierra has made public that they are discontinuing the production of 6mm 117 gr DTAC due to repeated failures. I do not mean to pick on Sierra but this is a recent example. ALL BULLET MAKERS HAVE BULLETS THAT FAIL AND MOST FAILURES ARE CAUSED BY THE MELTING OF THE CORE.

At Berger I am committed to making bullets Walt's way. I was not going to change the bullets in any way unless I was certain that a change would solve the issue and not affect precision. We have been working on this issue for many years. It became apparent that making the jacket thicker in key areas was likely to produce a solution. This test proved that we were correct.

The theory that the lead being too high in the nose was dismissed as a cause of bullet failure long ago. This test proves that the height of the lead in the nose does not affect failure. Mike, I will spell it out for you because I know you have a hard time keeping up with the facts already discussed.

Proof that the lead height in the nose does not cause failures: During this test the bullets that failed were made with regular jackets. The bullets that did not fail (not a single bullet) were made with thicker jackets. The outside dimensions on these bullets were exactly the same as they were made in the same set up and no adjustments were made to the ogive dies between the two bullets.

If the outsides of the bullets are dimensionally the same and the jackets of the bullets that did not fail are thicker then this means that the lead was higher in the nose of the thicker jacketed bullets (that did not fail).

I'll take this even further. The reality of nose deformation is that the nose of a bullet can "slump" when put under high pressure situations. When the "lead is too high in the nose" theory was being discussed the reason why it was linked to bullet failure is due to the nose defroming under the pressure of the bullet being fired. When the thicker jackets were shot during this test none of them failed but several rounds had blown primers. We did not have any blown primers when the bullets made with regular jackets were shot. Blown primers are a sign of increased pressure.

Let's go one step further. One of the very real results that occurs when nose deformation does exist is poor precision due to an inconsistent change of the ogive portion of the bullet. The one target that was shot for score was a 12 o'clock 6 (due to scope adjustments), 8-X's and 1-10. Also, those watching through spotting scopes commented on the consistency of the bullets impacting the same area of the berm.

Summary of the facts discussed on the "lead too high in the nose" concern:

Bullets made on regular jackets with lower lead line produce multiple bullet failures and no high pressure signs.

Bullets made on thicker jackets with higher lead line produce no bullet failures and some high pressure signs.

I hope this finally puts the "lead too high causing bullet failures" discussion to bed from those who frequent these forums. I would expect such a thing from a new visitor but Mike, you have been harrasing folks on these forums for a while and have read all of this before.

The twist rate of the barrels was 8.5". Before you go down this particular road (of ignoring the test results) this produces roughly 254,000 RPM which is well within acceptable limits.

Mike, I hope this helps someone and leaves you with little or nothing left to say. We'll see.

Regards,
Eric
 
"The theory that the lead being too high in the nose was dismissed as a cause of bullet failure long ago. This test proves that the height of the lead in the nose does not affect failure. Mike, I will spell it out for you because I know you have a hard time keeping up with the facts already discussed. . . .

I'll take this even further. The reality of nose deformation is that the nose of a bullet can "slump" when put under high pressure situations. When the "lead is too high in the nose" theory was being discussed the reason why it was linked to bullet failure is due to the nose defroming under the pressure of the bullet being fired. When the thicker jackets were shot during this test none of them failed but several rounds had blown primers. We did not have any blown primers when the bullets made with regular jackets were shot. Blown primers are a sign of increased pressure.

Regards,Eric[/QUOTE]

Eric, thanks for sharing your results! "Hillbilly" testing of the nose deformation hypothesis, leads me to believe that this just doesn't occur in any "normal" situation - over the years, custom bullets, made using J4 jackets, and of various calibers, shot through barrels of differing twist rates, and cartridges, thus, velocities, when recovered from snow drifts, have NEVER displayed ANY deformation of the nose section of bullets! Except for the land engravement marks, the recovered bullets look as though they could be fired again! How do we recover the bullets? We just wait until spring: once the drifts are melted, we pick the bullets up! :eek::D RG
 
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Eric

Will you be making the "thick" skinned bullets available by request, or are you potentially going to move the entire fleet over to that technology?

Thanks for chatting with me at SHOT, and thanks for the R&D efforts.

JeffVN
 
Complete new line of Bergers

Based on the results of this test we are going to introduce an entirely new line. The new bullets will be VLD-THICK or BT-THICK. These bullets are meant exclusively for the long range target shooters.

Our Berger VLD regular bullets have been too successful to discontinue. These thicker bullets will be an alternative for those who are concerned about bullet failures in their rifles.

These thicker jacketed bullets will be clearly designated as THICK on the label. It will be up to the shooter to decide which bullet suits their particular shooting needs.

Randy, as I expected we agree on this subject. We don't have much snow in Southern California but I would expect to find bullets in the same condition as you describe if we did. I hope you are well and that we survive these yahoos.

Regards,
Eric
 
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this thread is really very interesting in as much as the reason for the failures being core melting. have you considered changing the core mix ratios, to produce a higher temp core material. i've been shooting your standard vld's for a while now and am quit pleased with you product. i realize that changing the your core mix will be harder on your equipment as the core will be harder. it sounds like a simpler fix than having to come up with a new jacket design though. just an idea, to toss around. :cool:
 
sourdough said:
this thread is really very interesting in as much as the reason for the failures being core melting. have you considered changing the core mix ratios, to produce a higher temp core material. i've been shooting your standard vld's for a while now and am quit pleased with you product. i realize that changing the your core mix will be harder on your equipment as the core will be harder. it sounds like a simpler fix than having to come up with a new jacket design though. just an idea, to toss around. :cool:
Click to expand...

Eric may reply also - but I'm going to chime in. Counter intuitively, increasing the antinony content (making the cores harder) lowers the melting point of the alloy. RG
 
Comments above

I. The fact that the core partially melts is not the cause of the bullet failure but results because the jacket gets too hot.

The friction is between the bullet jacket and the barrel bore and the heat flows through the jacket to the core. Heat flow is always accompanied by a temperature drop thus the exterior portion of the jacket is hottest with temperature dropping toward the core.

The fact than part of the core melts, at around 630 F, means that the surface temperature of the jacket is much higher than 630 F.

At temperatures above 630, the strength of the jacket material is likely reduced.

Bullet failure likely occurs as the bullet exits the muzzle due to the reduced strength of the jacket material, due to overheating, and as a result of tensile stress due to a base pressure of 4000 psi to 12000 psi at the muzzle and centrifugal forces. The base pressure on the bullet, now with the bearing unsupported by the rifle bore, results in tensile stress in the jacket and that stress is increased further by the high rotational speed of the bullet.

The partial melting of the core probably does have a direct effect on the jacket tensile stress though. In the fastest twist barrels we shoot, the stress in the lead core is not sufficent to cause the core to expand radially into the jacket at normal temperatures. When the core partially melts, the molten lead and antimony must be contained entirely by the strength of the jacket, thus a molten core would increase the likelyhood of bullet failure in addition to the reduction in strength of the jacket material due to overheating.

II I can't agree that the test Eric ran demonstrates that lead high in the ogive does not cause bullet distortion.

First, in the past we discussed core material being high in ogive as being distructive to the bullet ogive jacket. But at that time the discussion was limited to a particular bullet or jacket, thus having the lead core higher in that jacket was worse.

But the actual criteria is the ogive jacket stress near the base of the ogive and that depends on the mass of the lead core above the beginning of rifling engravement, the maximum acceleration of the bullet, the diameter of the core at the stress plane (the plane normal to the long axis of the bullet and near the beginning of the land engravement of the ogive) and the thickness of the jacket at that plane. One should consider those stresses in bullet design and not be foolish by overstressing the bullet jacket.

I suspect that bullet catastropic failure might not be caused often or at all by overstress in the ogive jacket but distortion of the bullet can and likely occurs which can result in fliers.

III I believe the hottest part of a bullet occurs at the base of the bearing because that is where the dynamic core pressure is the greatest. By dynamic, of course is mean the bullet is accelerating at tremendous levels and the internal core pressure increases almost linerally from the top of the core to the bottom of the core. It is not exactly linerally because the core is a solid and its cross sectional diameter varies along the long axis of the bullet.

I have seen many bullets spew molten lead upon firing them through paper screens at 20 yards and one at 288 yards. One of the bullets that failed in that manner was fired out of a new barrel and I suspect that even though the barrel had been lapped by one of our premier barrel makers, it was still rough enough to cause enough friction to overheat the bullet.

All other bullets that have spewed molten lead were fired out of older bores with likely rougher surfaces that resulted in overheating of the bullets.

The one bullet that spewed molten lead on the 288 yard target was a 108 grain flat base 6mm bullet and went through the target sideways and the lead was spewing from the base of the bearing surface.

That is logically where the jacket will fail if the jacket thickness in the bearing area is constant. If one forces a bullet through a barrel at a constant velocity, the jacket surface friction should be relatively constant and results from the frictional forces of the normal force of the jacket being applied to the bore. But when the bullet is accelerated, as when firing out of a rifle, the internal core pressure will always be greater at the base of the bearing surface, thus the friction and jacket heating (with core heating lagging behind jacket heating) will be greatest at the base of the bearing surface. Thus the bullet jacket is heated by static frictional forces which are relatively constant across the bearing surface and dynamic frictional forces which increase steadily as one nears the base of the bearing surface.

Thus in designing a bullet it is important to consider the mass of lead core material above the base of the bearing surface. The more mass above the bearing base, the higher the core pressure, the higher frictional forces will be which will result in higher jacket temperatures.

A boat tail bullet made with the same jacket and same core in the same caliber as a flat base bullet, both having the same ogive shape will heat less at the base of the bearing surface and will be more reliable than the flat base bullet because the boat tail bullet has less core mass above the base of the bearing.

The above statement is not speculation. I have seen reference to it in tests back in the 1930's and I have tested it myself by machining boat tails on 6mm, 116 grain flat base bullets. Even though cutting a 3 degree boat tail bullet removed about half of the jacket thickness at the base of the flat base bullet, the reliability of the bullet was improved. I believe it is a result of less jacket heating at the base of the bearing surface. By machining the boat tail on the flat base bullet, the base of the bearing surface was moved higher where the mass of lead core above that plane was less which resulted in less dynamic core pressure, less friction and less heating.

One might think that machining half of the jacket away at the base would cause the bullet to fail but if you analyze the situation you will find that at the base of the core of a bullet the core pressure there, due to bullet acceleration, is very close to the propellant gas pressure behind the bullet. Thus the differential pressure is low and the stress is low on the diameter of the bullet.

The flat base of a boat tail bullet and flat base bullet is a different situation and needs to be considered apart from the comments above.

The spelling was not checked so forgive the errors.

Henry
 
Henry
If I understand your post you are saying that the bullets fail at the base.

If you read this post by Dave Tooley http://www.benchrest.com/forums/showpost.php?p=368536&postcount=32

The one bullet he was able to ascertain where it was failing was at the ogive/body junction.
So if I understand correctly you and Dave aren't in agreement on where the failure is taking place. Could you clarify that for me since maybe I am just not understanding?

I am in no way being argumentative, I am hoping to learn something and I greatly respect both your's and Dave's opinion.


RG or Eric,
Is there any reason to not use a pure lead core in a target bullet?


James
 
Chisolm said:
Henry
If I understand your post you are saying that the bullets fail at the base.

If you read this post by Dave Tooley http://www.benchrest.com/forums/showpost.php?p=368536&postcount=32

The one bullet he was able to ascertain where it was failing was at the ogive/body junction.
So if I understand correctly you and Dave aren't in agreement on where the failure is taking place. Could you clarify that for me since maybe I am just not understanding?

I am in no way being argumentative, I am hoping to learn something and I greatly respect both your's and Dave's opinion.


RG or Eric,
Is there any reason to not use a pure lead core in a target bullet?


James
Click to expand...

Yes, especially with the relatively fast twist rates (as compared to traditional benchrest) required for stabilization, by the bullets in question, core "stripping" (slippage between the jacket and core) as the bullet begins to rotate [down the barrel] is more likely with "pure lead" cores (see Rifle Accuracy Facts, by Harold Vaughn) . In all of my experience, short of specific barrels, which cause failures, alloyed cores make superior bullets - that is, where superior equates to precision.

Based upon empirical evidence, individual barrels are as big an issue as jackets: I have seen and had customers "report" from both sides of the coin - yes, with barrels from the same manufacturer, and varying chamberings, featuring the same twist rate(s), but with completely opposite results! :eek:
It appears the barrels featuring odd land/groove counts tend to be less destructive - especially in combination with 5R type rifling profiles.

My pal, Tom, has two barrels from one very good maker, purchased at the same time,then, chambered with my 6/250 Ackley Imp. reamer - at the same session, using the SAME components, one barrel destroys EVERY BERGER, Sierra and BIB bullet before the chronograph records 2900 FPS (the bullets "vaporize" before reaching the 100 Yd. berm), while the other barrel has yet to produce a SINGLE failure of any of these bullets and MVs in excess of 3100 FPS, which should also equate to considerably MORE pressure. "Go figgure"! Oh, that offender barrel shoots the Lapua 105 Gr. Scenar bullets quite well . . .

Last spring, Bill Niemi provided Tom and I with 100 sample 105 Gr. bullets, made with "thick" jackets - Bill was not at liberty name the source - he asked us to run those bullets through the "bullet wrecker" tube and report back. Tom shot the entire 100 without a single failure - and at 3100+ FPS no less! In order to make certain that the bullets weren't "going into the same hole", each shot was fired at a serarate "aiming "bull" - the distance was 200 yards . . and, once the rig was zeroed, the bullets performed quite pleasingly. Having followed this thread, I'm hoping that Bill obtained the jackets from Berger/J4, and they will eventually be made available to the custom bullet trade.:D

Then, this winter, an individual called - he was interested in trying my 108 Gr. FB for 600 Yd. and possibly some 1K work - since his platform featured a 1:7" twist barrel, I tried to talk him out of using/testing the BIB 108 - his formula is known to produce failure (I don't like hearing that the 108s will be shot through a 1:8" twist, which is 12% faster than necessary!)! But, the gentleman would settle for nothing less than, "seeing for myself ". So, off went a few of the FB 108s - he called back and ordered MORE - the bullets had proved excellent at 1K! Following my standard lecture, he stated that he was going to now chamber a 1:8: twist barrel [of the same make, as he had one on hand] and "laugh all the way to the podium" . . . but when we last spoke, the new 8" twist tube was destroying a fair percentage of the SAME bullets which had worked so well via the 7" twist!:eek::eek:

What do I KNOW for Certain about bullet failures? NOTHING IS ABSOLUTE. The variable set is large and dynamic. I do believe that, with the thicker jackets, Eric and Berger Bullets are onto a probable cure. If you're only slightly carzy, cut a bullet wrecking barrel back from it's current 28+" length, to 24": the friction reduction is [sometimes] obvious!;) Good shootin'! RG
 
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Dave's test

Chisolm,

You understood correctly. I believe the bullet jacket that fails due to overheating, fails at the base of the bearing surface. That would be near the base of a flat base bullet and near the base of the bearing boat tail junction of a boat tail bullet.

Several months ago, Dave and I discussed running a test to determine where, along the length of the bullet the molten lead was being ejected after the bullet leaves the barrel. Without going into detail, I believe it is impossible for the lead to be ejected out of the hollow point at the front of the bullet. (If you think differently, consider the decelleration of the bullet due to air drag compared to the centrifugal acceleration that the molten lead must overcome to reach the hollow point.)

I suggested to Dave that if he could find a worn out 30" long 6mm barrel in 12in. twist then shooting hot loads with flat base long range bullets, for example 116 or 121 grain Bibs might give the answer. The 12" twist would not stabalize the bullets then all one would have to do is shoot through a 20 yard target until a failed bullet went through sideways. This would also indicate that heating is the primary cause of failure, not twist.

Dave sent a scan of a target where he fired a bullet through a piece of 1/2" or 3/4" piece of plywood turned at 45 degrees. The idea was the plywood turned at 45 degrees would cause the bullet to tumble.

I agree that the plywood would likely cause the bullet to tumble but if that is the test you are refering to then I can't accept the results. First it did not appear to me that the molten lead was being ejected from a definate point. Second one has to consider the impact of a bullet at about 3000 f/s on a piece of plywood and what effect that will have on the bullet. That is not an acceptable way to test the effect we are looking for, in my opinion.
 
ok from what you are saying this is a frictional issue with a direct correlation between bullet jacket thickness and barrel. what is being tried is thickening of the jacket to impart more tensile strength to the jacket. adding or changing core mix ratios by the addition of antimony for harding, is obviously not the solution, as it imparts very little temperature increase to the mix. i was thinking more along the lines of additional tin, or zinc in the mix thus making the core harder but also raising the melt temp to closer to 795 degrees. i have also noted that the barrels being used are in the 30" range. could this be an issue that can be solved by shortening the barrel length to reduce the time of frictional heating? bore diameter can also be increased by 0.0005 this should reduce friction all by itself, while a softer jacket material will still upset enough the maintain accuracy. i do realize that palma shooters are using undersized bores to increase velocity and bullet seal, but they are not seeing the same issues with the larger projectiles, core volume adds it own help to the problem. berger has a good product line without changing its manufacturing processes or materials. from what i have been seeing discussed as the bore diameter goes down frictional resistance increases with the j-4 jackets. if this is correct then the use of cut barrels should give the same results as button rifled barrels. it may also be nothing more than the manufacturing tolerances when on the small side could be attributing to the failures. all failures could be attributed to the jackets being on the low side or the thickness spec, then pressure cut by the bore. if this is the case a major redesign of the jackets would be unnecessary. it could be solved by moving the jacket thickness tolerances up 0.001 to 0.002. if it turns out to be a cut rifling issue, which it mite, then changing a wining design will just be chasing your tail, as there are many completive button rifled barrels out there. i don't think that berger should produce a produce that is a do all end all. i don't think it should be required to work in every barrel that is manufactured out there. another thing to look at is what is the differences between the mass jacket ratios for other bullets that are not have this problem and the ones that are. once you know what the differences are it should point to the answer to this problem.
 
RG and Henry
Thank you both both for your great responses.

Henry in the question of lead being forced out the tip would it be possible for the centrifugal forces to cause the lead to displace the antimony and force it out of the tip? I don't know I just know you can accomplish some weird stuff with a centrifuge.
As far as do I think that happens, I am on the side of I don't have a clue what happens and am glad people like you guys share your knowledge.

James
 
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