Weighing Cases & Powder

G

Gene Beggs

Active member
We benchresters tend to be nit-picky perfectionists and are always looking for ways to improve the quality of our loaded rounds. Some feel it is beneficial to sort cases by weight while others (myself included) feel it is a waste of time. Same goes for weighing each and every powder charge. Try the following experiment and I think you will agree. In addition to your normal loading equipment, you will need a good chronograph and powder scale.

For this experiment, use only one case; one that has been fired two or three times. Load and fire the case ten times with carefully weighed charges, chronographing each shot. Note the extreme spread.

Now, go back to the loading block from which you took the one case and load ten of those cases with thrown charges from your measure using your favorite technique and fire those ten over the chronograph. I'm betting you will see little or no difference between the extreme spreads; sometimes, it will actually be less than with the weighed charges! This is an eye-opening experiment; try it, I think you will be surprised.

So,,, if it's not the cases or variations in powder charge that causes one round to be faster than another, what is it?? You tell me. Some say it is variations in neck tension, but I don't think so. Several times during the past few years, I have loaded twenty 6ppc rounds and every one of them felt the same when I seated the bullets, but the extreme spread of those twenty rounds might be 43 or 38 or whatever, sometimes as much as 53 fps. What's going on? The only explanation I can offer is it is the primers. That is the one variable over which we have no control other than switching to a different brand or lot number.

What do you think?

Gene Beggs
 
Gene, I think that you are correct on primers. The primers have a certain amount of energy released and the more this varys the more variance you will have in ignition and total energy produced and that is why the hotter loads are quite often the one that is more accurate. The more powder, the more energy, and the less effect the varience of the primer energy will have on the total output. I hope this makes sense.
 
I think some of the 1000 yd. guys weigh their primers? Maybe there's something to it. I don't like weighing anythying, but I do buy my 220R brass from Hoen sales already weighed. I shoot outside and blame everything on the wind:)
 
JohnVm said:
Gene, I think that you are correct on primers. The primers have a certain amount of energy released and the more this varys the more variance you will have in ignition and total energy produced and that is why the hotter loads are quite often the one that is more accurate. The more powder, the more energy, and the less effect the varience of the primer energy will have on the total output. I hope this makes sense.
Click to expand...

Yes John, your suggestion makes perfect sense. The times in which I have observed single digit extreme spreads were when I was shooting hot loads. Here, I'm speaking of the 6PPC cartridge. Strangely enough, I experienced my best match results ever at the 2003 NBRSA Nationals in Phoenix winning the HV Grand shooting light loads of 8208 in the 26.9 to 27.7 grain range. Go figure. :rolleyes: There is still much we do not know.

Later,

Gene Beggs
 
Gene

Just brainstorming. Is it possible that Calfee's thoughts on "relaxing" could provide some insight? Or does that just apply to rimfire???

Tony
 
Could it be?

Gene,
Could that spread in fps be within the standard error tolerence of the chronograph? The spread is about 1/10th or .01 of the velocity if my math is correct. :)
 
Food for thought

Gene: I am a proponent of weighing charges, even if I don't always do it:rolleyes:
While getting ready for my 6mmBeggs, I spent some time with the powder measure throttled down to the level I expect charges to be, so I could build a referrence chart for my powder bottle. I use a Neil Jones measure, and set it to drop 25.0gr H4198 (or close). In 20 drops, the measure gave me a range of loads from 24.9 to 25.2 with no rhyme or reason. I did this twice. Then I dropped ten loads into the pan and it weighed 251.2gr. A second ten weighed 251.1gr, and a 3rd ten weighed 251.2 gr again. SO, the ten drop average is EXTREMELY close, yet individual drops vary by as much a 3 tenths. A Harrels I had a while back did the same thing.
I just don't like the idea of getting that 24.9gr load into the same group as a 25.2gr load. At least nobody has pointed to the advantage of doing that on purpose.
Second, I can't help thinking about barrel heat (even with a few fouling shots) and how that may bear on the velocity readings. Did you allow the same time between shots with 10 cases as with the single case reloaded 10 times?
By the way, that 25gr H4198 load was a "for instance", and was used as an example.
Keep up the good work!
Bryan
 
gene

One thing we have noticed with our 30PPC's is we are getting very good ES and SD numbers when shooting over my 35-P Chrono. Almost always in single digits. Much better than what I normally get with my 6PPC's.
I have no explanation for this.........jackie
 
Primers ?

Hey guys, the primer thing is real interesting. Has any body come up with a way to measure primer energy without powder involved.I seem to remember an article in PS a couple years back where somebody(sorry, I can't remember what I had for lunch)had photos of different brands of primers going off,and some seemed to burn hotter than others,but was any one brand tested for consistency, Hmmmmmm?
Joel
 
Bearing surface (bullet body or shank length) matters ...

Gene: Here is an outstanding article I read yesterday that might shed some light on another aspect of what you've found: http://www.6mmbr.com/medlerTUBBBSC.html. Bottom Line: Sorting bullets by bearing surface/body/shank length can improve Extreme Velocity Spreads (ES) and improve accuracy. Why? As the article points out, variances in bearing surface creates variances in friction which leads to variances in pressures which in turn leads to inaccuracy.

I sorted a box of Sierra MatchKing 69 grain HPBT's and ended up with two groups. One group's bullets measured .507 to .508 and the other .502 to .503. Not a bad difference within each group. Only .001 difference but .005 between them. Needless to say I'll shoot them as segregated groups.

I spoke to a Sierra ballistician today and asked if the difference was because they may have come from different dies and mixed into a box. He said no, they know that they have a problem and are working on it. He said what they found was that the lube they use and the way it's used causes bullets in the morning to have shorter shanks and the bullets later in the day to have longer shanks.

I'm not bullet smart enough to comment on what he told me but I certainly understand now that if I use Sierra bullets or others, sorting by shank length or bearing surface, might improve my results.
 
Bryan,

You bring up a good point when you asked if I waited the same amount of time between the ten shots. No I'm sure I did not. When I loaded the same case ten times, it surely took more time between shots even though the loading room is right next to the firing room.
 
I've noticed (sometimes, but not always) that a .003 to .005 seating depth change will increase or decrease the ES by a considerable amount. The first time I ever noticed it I changed the depth back and shot another string over the chrono just to verify what I thought I'd observed.......sure enough, it was for real...that time.

I have tried to chrono those loads that shoot noticably better in the wind than most, in hopes of identifying something unique that I could look for during load development. It seems that there is no real magic charactaristic (aside from velocity) to watch for. In fact, some of the best loads exibit the scariest spreads.

I remember a PS article in the mid 90's about thrown vs. weighed charges. The conclusion was that thrown charges out-shot weighed charges. The (assumed) reason was that the powder orientation within the case was more consistant than when dumped through a funnel. The powder, in theory, burned at a more consistant rate because of this orientation. Opinions?

-Dave-:)
 
Dave Short said:
I remember a PS article in the mid 90's about thrown vs. weighed charges. The conclusion was that thrown charges out-shot weighed charges. The (assumed) reason was that the powder orientation within the case was more consistant than when dumped through a funnel. The powder, in theory, burned at a more consistant rate because of this orientation. Opinions?
Click to expand...
If that's the article I'm thinking of, it was by McPherson & was all over the map. It included things like velocity variations with about 6 grains of powder in a .38-40 case, depending on how the powder was oriented (all at the front vs. all at the back, etc.). The particular thing you mention was, as I remember, some variations where how you charged a case could give a compressed load done one way, and just a full case done another. Best I remember, McPherson speculated there would be more variation when using a powder funnel (i.e., weighing), unless maybe you used his swirling technique? Typical McPherson BS.
 
Last edited:
jackie schmidt said:
One thing we have noticed with our 30PPC's is we are getting very good ES and SD numbers when shooting over my 35-P Chrono. Almost always in single digits. Much better than what I normally get with my 6PPC's.
I have no explanation for this.........jackie
Click to expand...

Most interesting Jackie. The first time I experienced this phenomena was when Shelley Davidson and a couple of other shooters brought their 30 BR's to the tunnel. Their extreme spreads were always amazingly low. My gut feeling is that it has something to do with case capacity versus bore diameter and bullet weight. The Russian 7.62 X 39 cartridge is a classic example of this; it generates velocities all out of proportion to its size.

Later,

Gene Beggs
 
Charles E said:
If that's the article I'm thinking of, it was by McPherson & was all over the map. It included things like velocity variations with about 6 grains of powder in a .38-40 case, depending on how the powder was oriented (all at the front vs. all at the back, etc.). The particular thing you mention was, as I remember, some variations where how you charged a case could give a compressed load done one way, and just a full case done another. Best I remember, McPherson speculated there would be more variation when using a powder funnel (i.e., weighing), unless maybe you used his swirling technique? Typical McPherson BS.
Click to expand...

I don't remember the article in detail, but it was not a small charge of fast burning powder in a big black powder case. It was a modern case, using a case full of powder. It was actually fairly well written, but the conclusions were not very well supported.

-Dave-:)
 
Nader said:
Hey guys, the primer thing is real interesting. Has any body come up with a way to measure primer energy without powder involved.I seem to remember an article in PS a couple years back where somebody(sorry, I can't remember what I had for lunch)had photos of different brands of primers going off,and some seemed to burn hotter than others,but was any one brand tested for consistency, Hmmmmmm?
Joel
Click to expand...

Joel, I remember seeing two such articles where photos were used to show the flash that each primer produced. What I would like to do is devise some way of measuring the energy/pressure produced by each individual primer. Could we use a recording pressure gauge hooked up to a barrel stub installed in an action? A ball in a clear tube? or whatever? Think about it.

GeneBeggs
 
Gene:

Primers are the topic of two discussions in "The Benchrest Shooting Primer." Probably the two you're talking about. One is "Primer Tests" by Steve Chernicky, December 1985, pages 131 through 135. It covers the tests and equipment used. Quite comprehensive. The other one, "More on Primers" is covered on pages 8 through 10. Both show flash photos. Hope this helps.
 
abintx said:
Primers are the topic of two discussions in "The Benchrest Shooting Primer." Probably the two you're talking about. One is "Primer Tests" by Steve Chernicky, December 1985, pages 131 through 135. It covers the tests and equipment used. Quite comprehensive. The other one, "More on Primers" is covered on pages 8 through 10. Both show flash photos. Hope this helps.
Click to expand...

Thank you Art. It's most appreciated.

Gene Beggs
 
Gene,

a few points here, I am surrprised that nobody has mentioned it. In the first scenario you speak of 1 case (fireformed a few times) then loaded ten times for an extreme spread, standard deviation test. In the second scenario you speak of ten cases, all very close fired for a string to find extreme spread, standard deviation etc.

My question is what is going on with the barrel all this time? In the first scenario how long between shots to load the cases and fire them, has the barrel cooled? was it warmed up before the string started? was it timed fire so that the temperature of the barrel was kept constant?

In the second scenario, would you keep the same barrel temp as the first scenario? how long in the warm chamber would a case be allowed to sit (and possibly warm)?

To get results from a test like this you have to have a standard method so that the test results show you what you were looking for, with respect to brass, not barrel temp.

Does this add any helpfull information to your test?

Paul
 
pbike said:
Gene,

a few points here, I am surrprised that nobody has mentioned it. In the first scenario you speak of 1 case (fireformed a few times) then loaded ten times for an extreme spread, standard deviation test. In the second scenario you speak of ten cases, all very close fired for a string to find extreme spread, standard deviation etc.

My question is what is going on with the barrel all this time? In the first scenario how long between shots to load the cases and fire them, has the barrel cooled? was it warmed up before the string started? was it timed fire so that the temperature of the barrel was kept constant?

In the second scenario, would you keep the same barrel temp as the first scenario? how long in the warm chamber would a case be allowed to sit (and possibly warm)?

To get results from a test like this you have to have a standard method so that the test results show you what you were looking for, with respect to brass, not barrel temp.

Does this add any helpfull information to your test?

Paul
Click to expand...

All good points Paul. No, I made no effort to time the shots or maintain the same barrel temp. My "tests" tend to be quick and dirty and my experiments more like what one would encounter during match conditions.

GeneBeggs
 
You must log in or register to reply here.
Back
Top