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Case weight and group size

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Case weight and group size Empty Case weight and group size

Post by jlow Sat Jul 06, 2019 9:15 am

Sorted my range pickup FC brass and found two batches of weights 57-58 grains and 62 to 63 grains.

In precision rifle reloading, we weight sort our brass because heavier brass means more brass and less case volume.  That usually means more pressure and affect POI.  We of course shoot long distance 300-1000 yards where a slower round would have more drop and this is why POI changes.

The question is with pistol where we are shooting short distances i.e. 25-50 yards. does brass weight/case volume/pressure/slight MV differences affect group size?  I know the theoretical answer is YES, but has any one tested this?  FWIW, I know we should always use the same headstamp brass but is that because of the differences in wall thickness (which affects crimp) or is it both?Case weight and group size Img_1816

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Post by Dr.Don Sat Jul 06, 2019 9:55 am

IMO weight sorting cases is a waste of time for pistol.  At 25yds even headstamp sorting is a waste.
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Post by jlow Sat Jul 06, 2019 9:56 am

Hmmm...  Thanks for the response.  That's interesting, how about 50 yards?

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Post by Dr.Don Sat Jul 06, 2019 9:59 am

I would stick to the same headstamp at 50yds, but weight sorting is still a waste to me.  A lot of the things that make a real difference in precision rifle make so little difference in our short range sport it's extremely difficult to even measure their effect.
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Post by jlow Sat Jul 06, 2019 10:23 am

Thanks!  Still interested in anybody who has first hand experience measuring to see if it makes a difference.

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Post by S148 Sat Jul 06, 2019 12:23 pm

Case volume can effect velocity, as shown in the link below. Velocity could affect accuracy but I don't know of any source that looks at all those factors together. 

https://americanhandgunner.com/gear/exclusive-handloading-p-brass/

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Post by james r chapman Sat Jul 06, 2019 2:08 pm

I sort headstamps because of variations in wall thickness causing crimp problems with bullets allowing some to slide  into the case when seating. I use a specific process that allows the bullet to seat part way before crimping. For example, star line, Winchester and federal work fine , R-P allows the bullet to drop on the powder.
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Post by fc60 Sat Jul 06, 2019 2:14 pm

Greetings,

From experience with the 32 S&W Long wadcutter I can offer this...

Cases with thick webs/midsections shoot higher velocities than those designed for full length wadcutters.

Example, Lapua cases loaded with 1.7 grains of Bullseye and a 98 grain bullet average about 700 FPS.

The same recipe with Federal cases results in velocities about 730 FPS.

Cheers,

Dave
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Post by dronning Sat Jul 06, 2019 3:50 pm

Check the difference in velocity between the 2 weights.
If I remember right a 50fps change in velocity will change a bullet impact @50yd by about .35".
- Dave
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Post by jlow Sat Jul 06, 2019 5:52 pm

Thanks guys!

From my own experience working with a tapered crimp, case wall thickness (and length of course) has an effect on pressure/velocity which makes perfect sense if one considers how a taper crimp works.  This is certainly a reason to use brass with consistent wall thickness.  Since we cannot turn necks with pistol brass, the only way is to use the same headstamp.  I’ve done some work looking at case wall thickness and know that they vary very significantly between case headstamp and is one big reason why different headstamp brass has different case weights.

I took some time to look at what is responsible for the two groups of brass weights for the FC brass – the results are in this Excel sheet image.

The first thing I looked at is wall thickness.  I chose 5 different weight range with 3 samples each.  Weight brass with electronic balance (A&D FX-120A) and measured wall thickness with a Mito electronic ball micrometer.  Because of neck variance, I measured 3 random spots for each piece and average the numbers.  As can be seen with the bottom graph. The wall thickness are not significantly different for the brass which range from an average of 56 grains to 64 grains.

I next tested case volume using a tried and true method with rubbing alcohol.  Weight the case empty and fill with a level meniscus.  As can be seen in the top graph, there was excellent negative correlation between brass weight and alcohol weight with an R2 value of 0.9 (1.0 is prefect correlation).  As expected, the heavier the brass, the less alcohol volume it holds.

Since the case wall thickness was not responsible for the increase weight, it is clear that the case have thicker head.

So at least for the FC brass, the heavier brass do not have thicker walls but the thicker head would be responsible for a decrease in case volume.  Would be interesting to see if it results in a difference in MV and POI.

I should add that using weight difference in alcohol as a reflection of volume, there is an approximate 7% difference in volume between the two extremes - that seems significant.

Case weight and group size Untitl10

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Post by GerhardG Wed Jul 17, 2019 5:16 pm

Greetings,
 I believe that sorting brass by headstamp for competition has a benefit in relation to the accuracy of the crimp pressure and bullet seating depth. I worry about my Dillon RL550B progressive due to four operations occurring per stroke. For my precision reloads I run my ammunition through the crimp station only with no other operations in the press. I feel a difference in my handle pressure. The proof for me is if I take a few and go through the crimping stage a third time the handle pressure is nill. 
 HAs anyone else tried this and noticed a difference or measured it? 
 On another note, I may have to watch out for my Primer depths as they can be effected via case variations and other factors. I am considering going to single-stage operations for better control.


Last edited by GerhardG on Wed Jul 17, 2019 5:36 pm; edited 1 time in total (Reason for editing : Improve comment)

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Post by Gary Wells Fri Jul 19, 2019 9:31 pm

I believe that a shooter would have to be very good to notice a difference even at 50 yds with handgun shooting. I reload only 1 brand (RP) of cases as I bought 7500 new, unprimed, mickel plated cases years back, kept 5000, &n sold the balance. I do believe tjat you will get more consistent OAL's re=loading 1 brand only. Easier to ID at the range too. Now on the another note & reason I lost my right eye a few years back and my shooting leaves a lot to be desired.

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Post by Joe Morgan Fri Jul 19, 2019 9:34 pm

jlow wrote:Thanks guys!

From my own experience working with a tapered crimp, case wall thickness (and length of course) has an effect on pressure/velocity which makes perfect sense if one considers how a taper crimp works.  This is certainly a reason to use brass with consistent wall thickness.  Since we cannot turn necks with pistol brass, the only way is to use the same headstamp.  I’ve done some work looking at case wall thickness and know that they vary very significantly between case headstamp and is one big reason why different headstamp brass has different case weights.

I took some time to look at what is responsible for the two groups of brass weights for the FC brass – the results are in this Excel sheet image.

The first thing I looked at is wall thickness.  I chose 5 different weight range with 3 samples each.  Weight brass with electronic balance (A&D FX-120A) and measured wall thickness with a Mito electronic ball micrometer.  Because of neck variance, I measured 3 random spots for each piece and average the numbers.  As can be seen with the bottom graph. The wall thickness are not significantly different for the brass which range from an average of 56 grains to 64 grains.

I next tested case volume using a tried and true method with rubbing alcohol.  Weight the case empty and fill with a level meniscus.  As can be seen in the top graph, there was excellent negative correlation between brass weight and alcohol weight with an R2 value of 0.9 (1.0 is prefect correlation).  As expected, the heavier the brass, the less alcohol volume it holds.

Since the case wall thickness was not responsible for the increase weight, it is clear that the case have thicker head.

So at least for the FC brass, the heavier brass do not have thicker walls but the thicker head would be responsible for a decrease in case volume.  Would be interesting to see if it results in a difference in MV and POI.

I should add that using weight difference in alcohol as a reflection of volume, there is an approximate 7% difference in volume between the two extremes - that seems significant.

Case weight and group size Untitl10

It's nice to see data instead of old wives tales and the usual gatekeeping (I've been accused of that back on the lava days), but really, does any of the above result in significant changes in group sizes at 50 yards?

Can I limit the discussion to that question and hope to get a meaningful answer?

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Post by jlow Sat Jul 20, 2019 8:51 pm

I wish I could answer that question, but I cannot.  

The reason is the old chicken and egg dilemma.  Basically I am working up a load for my pistol and I am not there yet.  On my way there, I am looking at variables that I can control and that MIGHT affect group size - and this is one of them.

Obviously since I don't yet have a load that shoots well consistently, it is impossible for me to test this question for an answer.  Theocratically a different in case volume will affect pressure and all that follows.  But that is not an actual answer from actual testing.  It of course does not stop someone else with a good shooting load from running the test - I have no problem with it.

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Post by Jon Eulette Sat Jul 20, 2019 8:59 pm

What is your test pistol; Make, builder, barrel?
Thanks
Jon
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Post by DA/SA Sat Jul 20, 2019 9:09 pm

Jon,

From one of the other threads:

"Mounted the gun which is a SA XDm 5.25 Competition 9mm. "
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Post by Jon Eulette Sat Jul 20, 2019 9:12 pm

Oh yeah....thanks.
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Post by Jon Eulette Sat Jul 20, 2019 9:15 pm

If I was going to spend time testing poly guns I would take a piece of aluminum plate and drill Ransom pattern on it. Then attach a upside down scope mount to it. Then clamp pistol to the Ranson fixture with the light rail.
I've made similar insert for MG2
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Post by DA/SA Sat Jul 20, 2019 9:31 pm

Just my opinion, but it seems like a tail chase so far, as it's a new Ransom Rest, being used by someone that has never used one, testing a pistol of unknown accuracy, shooting ammo that is unknown...

I believe I would at least try to find a pistol and ammo combo of known accuracy and use that to sort out the Ransom Rest and get some consistency with that for a starting point. At least you would have an idea if your RR technique and setup was consistent.
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Post by sharkdoctor Sat Jul 20, 2019 9:59 pm

The OP's dilemma is perhaps one of perspective.  An egg is a chicken's way of making another chicken, but a chicken is an egg's way of making another egg.  The OP can't test how parameters affect a precision load, because the OP doesn't have a precision load.  One has to start somewhere.

There are many precision/good loads for 9mm presented here on the list. I believe they are pretty universal, in that they work pretty well in most guns we use.  To tune the load to a single pistol, if it actually makes a difference, usually takes much more testing and analysis than most are willing to undertake.  And for most Bullseye shooters the loads are "good enough".  We can't measure pressure curves, bullet dwell times, barrel nodes, antinodes etc. We are pretty much limited to velocity and bullet precision of impact, the latter being the over-riding criterion.

Why not start with, say, 115 gr. Hornady HP XTP's and an appropriate powder and charge, with which many shooters have had good success, make careful modifications, test a variable and analyze?  Afterall, one is looking for a change in baseline - what variables may affect system precision.  I am sure many of us would appreciate and could use the data and results.

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Post by willnewton Sun Jul 21, 2019 7:40 am

Posts obsessing over minute case details (weight, length, thickness, etc.) by rank.

Master/High Master 10%
Expert/Sharpshooter  25%
Novice 40%
“I came over from rifle shooting” 120,000%  Laughing

It is good to see you paying attention to details, but in the beginning case dimensions are the least likely to impact your score.  You *might* make a 1/4” improvement in your group, but it won’t affect your score much at all until you are shooting at the highest level.

Meanwhile dry firing with a focus on learning triggering, grip, and stance can reduce your group size 50% or better, which will make a massive difference in your score.

Many of the details that matter on a rested long range rifle just don’t come in to play when dangling a pistol at the end of one arm while standing unbraced.

I am not trying to discourage you, as a matter of fact, keep up your research because it keeps your head in the game.  Finding connections between various disciplines helps keep the sport interesting.  I just want to temper your expectations and drop some hints at details to explore that will REALLY move the needle on your score.

Thanks for sharing your info, keep it up!
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Post by jlow Sun Jul 21, 2019 10:27 am

Folks, I would think the relationship of case weight and group size would be of interest to anyone interested in precision reloading for pistol i.e. willnewton comment that it “might make ¼” improvement in groups”.  

Other than not being able to test whether the different FC cases with different weights affect precision, my reloading effort with my polymer pistol really has nothing to do with this thread – so it would be useful to stay on topic.

I do appreciate constructive inputs i.e. like the plate/scope, different loads idea but that is best discussed in my other threads specific to working with the RR with the polymer gun.

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Post by dronning Sun Jul 21, 2019 1:22 pm

jlow wrote:Folks, I would think the relationship of case weight and group size would be of interest to anyone interested in precision reloading for pistol i.e. willnewton comment that it “might make ¼” improvement in groups”.  

Other than not being able to test whether the different FC cases with different weights affect precision, my reloading effort with my polymer pistol really has nothing to do with this thread – so it would be useful to stay on topic.

I do appreciate constructive inputs i.e. like the plate/scope, different loads idea but that is best discussed in my other threads specific to working with the RR with the polymer gun.
To be quite frank IMHO it's a waste of time.  I know High Masters that shoot mixes cases on the short line and they consistently clean targets and they would not do it if it would impact their score.  

On the long line they shoot the same head stamp brass and for big matches many will use new Starline brass because of it's consistency in length.  45 brass shrinks with each firing and not the way I thought either. see link
http://massreloading.com/loading45ACP.html

- Dave


Last edited by dronning on Fri Jul 26, 2019 10:16 pm; edited 1 time in total
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Post by David R Sun Jul 21, 2019 2:34 pm

I have read the whole reloading section from post one to here. The biggest thing I picked up is "Find a load that works and stick with it" Next is "Spend your time trying to imporve your shooting skills or Shot Process instead of trying to find a magic load."

For me, I bought a couple boxes Federal 185 SWC, the match ones and tried to get my reloads to shoot as well as them. I have spent a lot of time doing load development and testing. I would rather practice.

What size of group are you working wiht now? What do you expect to get?

Folks will tell you here that bullet type is the biggest thing to make a difference. More important than weighed powder drop, more than weighed cases, more than type of primer.
Best of luck
David
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Post by jlow Sun Jul 21, 2019 3:19 pm

Hey, it's OK.  I decided to share something that I found that I think may be of use to someone.  But as it is with these things, I understand some think it is a waste of time.  Life goes on. Smile

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