Myth Busting Pre-Resized Brass Affect On OAL Variance - Progressive Press

[9mmepiphany]

And people laughed at me when I started loading RMR FN bullets in preference to the more traditional RN

 

[RecoilRob]

It makes sense that on a progressive press when removing the resizing load there will tend to be less deflection and hence more accurate seating. Things that can rotate will by necessity have some play and when presented with the effort of resizing that plate is going to tilt a bit, and with the seating happening on the other side it's no surprise that the OAL moves a little.

 

[LiveLife]

Here is summary of OAL variance of reloading regular vs using pre-resized brass. The results illustrate the benefit of using pre-resized brass to reduce OAL variance on progressive press (Pro 1000), even with mixed range brass.

BLAZER - 9mm RMR 115 gr FMJ:

• Regular: 1.115" - 1.118" = .003" OAL variance
• Pre-resized: 1.115" - 1.116' = .001' OAL variance

R-P - 9mm RMR 115 gr FMJ:

• Regular; 1.115' - 1.118" = .003" OAL variance
• Pre-resized: 1.115" - 1.116' = .001" OAL variance

WIN - 9mm RMR 115 gr FMJ:

• Regular: 1.114" - 1.117" = .003" OAL variance
• Pre-resized: 1.114" - 1.115" = .001" OAL variance

BLAZER - 9mm RMR 124 gr FP:

• Regular: 1.070" - 1.072" = .002" OAL variance
• Pre-resized: 1.069" - 1.070 = .001 OAL variance

 

[Doublehelix]

This thread was meant for progressive presses where resizing operation may affect bullet seating operation.

I agree and understand, but I guess my point was that I do not see any difference in COAL variation numbers between the LCT and my progressive press. (I see about the same variations.) If your premise was true, I would expect to see less variation with the LCT.

Also, differences of .001-.002" between techniques seems so small as to be statistically insignificant (a human hair is approximately .004").

I hear your comments about "stacked tolerances", and I can see where you are going, but the other variations that go into the stacked tolerances are there for *both* techniques, which means to me, they become a constant across both equations. You can't claim stacked tolerances for one technique and not for the other. The variability due to these other factors is there for both techniques, so you can take that additional variability out of the equation, and you are left with .001-.002" COAL difference. Period.

I am not saying that this COAL difference does not add or detract to the shown accuracy, but I am not sure it is worth the extra effort (IMHO) of pre-resizing the brass. Obviously, YMMV.

In fact, I would further postulate that manufacturing tolerances in bullet manufacturing could account for part of the differences shown.

This is an interesting discussion, but I am still not convinced that I am going to start pre-resizing any time soon!!!

Thanks for all of the effort you put into your Mythbuster threads! We all love them and they make us think!!!

 

[egd]

Yes. Thanks for these mythbuster threads. I learn from them.
But, I have a variable to throw in also. If I understand your conclusion is that if one pre-resizes cases there will be less oal variation due to the decreased stress/flex of resizing the case on the press. But what about lubing the cases. That puts less stress/flex in much the same way does it not? Would that not be equivalent to pre-resizing? What if one did both?? AAHH, where does it end?

 

[mdi]

Nope it was a serious question. I don't use a progressive press and all the steps mentioned are done to mebbe 100+ at once (depending on the caliber). I'm using a Co-Ax and I "batch load" so sizing is done to a bunch of cases. Then measuring and inspection is done to the cases, and so on...

 

[LiveLife]

I can't say I've heard of "pre-resizing" Does one resize before resizing?

He's just pulling your chain for doubling up.

No, just resizing in separate step.

Nope it was a serious question.

I don't use a progressive press ... I'm using a Co-Ax and I "batch load"

The shellplate tilt/deflection affecting OAL variance is only applicable to progressive press using shellplate.

 

[LiveLife]

For those of you interested in the shellplate tilt/deflection of Pro 1000, this is repost from another thread - https://www.thehighroad.org/index.php?threads/new-auto-breech-lock-pro.832974/page-8#post-10779934

Of course, other progressive presses that mount ram under the center of shellplate, tilt/deflection of shellplate will be slightly different than Pro 1000/Pro 4000 which mount ram under Station 1.


Pro 1000 shellplate carrier uses offset ram mount similar to the new Pro 4000 (see picture below). When the shellplate is indexing (rotating without load), the bottom of shellplate does not contact the carrier/subplate as there exists a very small gap (the shiny wear circle you see on bottom of shellplate is from the ball bearing which applies tension to shellplate to "lock" into station). But when the shellplate is under load, limit of shellplate tilt/deflection is set by the bottom of shellplate contacting carrier/subplate (either Station 1 when resizing or Station 2/3 when seating bullet/flaring only).

This is demonstrated when sizing effort is harder (which pushes the entire shellplate down) and produces slightly longer OAL while when seating/flaring only (with no brass in Station 1), OAL is shorter.

The shellplate carrier is firmly mounted to the ram but the shellplate 'free-floats" inside the carrier attached to the center hub that hex "action rod" goes through and when you rock the shell plate, you are feeling this play. If you look at the picture below, there is no bearing the shellplate/center hub turns on as they were meant to "free-float" when there is no load on the shellplate.

So it's the top of carrier surface that is providing travel limit for the shellplate which determines the OAL variance of the loaded rounds.

Advantage of mounting the ram under Station 1 where resizing takes place, although more effort is applied on the ram, bottom of shellplate under the brass being resized contacts the carrier/subplate limiting further travel, theoratically will have less affect on tilt/deflection of the shellplate. Whereas, progressive presses that mount ram under the center of shellplate can tilt using the subplate as the fulcrum.

The new Pro 4000, which also off-set mounts the ram under Station 1 (with long case slider), looks to use similar principle but until we actually load some rounds, we won't know how much OAL variance the new press will produce.

 

[LiveLife]

I hear your comments about "stacked tolerances", and I can see where you are going, but the other variations that go into the stacked tolerances are there for *both* techniques, which means to me, they become a constant across both equations.

I am not saying that this COAL difference does not add or detract to the shown accuracy, but I am not sure it is worth the extra effort ... of pre-resizing the brass

Your points are very valid.

The reason why I started being focused on details of reloading variables is when we discussed consistency of shooting groups at 50/100 yards with pistol caliber carbines. jmorris posted the virtues of using 10 shot groups instead of 5 shot groups as 10 shot groups provide more information which I agreed with and since have used 10 shot groups for all of my accuracy testing.

Of course, we already myth busted the accuracy of digital scales (down to .02 gr resolution) verified by Ohaus ASTM Class 6 check weights down to 5 mg (.077 gr) and thanks to Walkalong, accuracy of calipers with Vermont Class ZZ +/- pin gages as we found not all jacketed bullets are sized the same to use as a gage - https://www.thehighroad.org/index.p...re-sized-the-same.818806/page-2#post-10567453

Then Bart B. posted the virtues of counting everything, including flyers as all the holes on target are the sum of reloading variables we use. That's when I stopped and rethought EVERYTHING I have done reloading and accuracy testing wise to see if I could remove as much variables as possible so my accuracy testing was more standardized, especially with mixed range brass. Yes, I could start with a box of new Starline brass but that won't directly help THR members using mixed range brass.

So I looked at all the reloading variables I could standardize that were measurable and repeatable:

• Bullet sizing/diameter difference (keep in mind lot to lot variation exists) - https://www.thehighroad.org/index.p...re-sized-the-same.818806/page-2#post-10567453

• Neck tension and bullet setback - https://www.thehighroad.org/index.p...nd-bullet-setback.830072/page-3#post-10715550

• Accuracy of digital/beam scales verified by Ohaus ASTM Class 6 check weights - https://www.thehighroad.org/index.php?threads/revisited-myth-busting-digital-scales.821449/

• Accuracy of calipers verified by Vermont Class ZZ +/- pin gages - https://www.thehighroad.org/index.p...ks-for-digital-calibers.821135/#post-10545265

• Long vs short OAL (greater neck tension for more efficient powder burn/chamber pressure build vs gas leakage) - https://www.thehighroad.org/index.php?threads/myth-busting-oal-col-long-vs-short.819257/

• Reducing OAL variance on progressive press (Which is this thread)

• Powder charge variance (My next myth busting thread so stay tuned - There's surprise for those interested in Promo ... Alliant changed granule size! ... maybe Paul heard my incessant grumbling about Promo granule size/metering? )

• Primer performance (Which primer produces smallest groups? The myth busting thread after Powder charge variance thread)

• Powder performance (Muzzle velocities/SD vs group size - The "holes on target", the end result I am working towards ... smallest group combination with mixed/sorted range brass)

So that's why I am "sweating" the little details.

These minute details may not benefit casual reloaders wanting range blasting ammo that just needs to go bang, but for many match shooters pushing the limits of accuracy, I am certain much of my work can translate to smaller groups on target.

 

[LiveLife]

In fact, I would further postulate that manufacturing tolerances in bullet manufacturing could account for part of the differences shown

I believe many would agree that bullet (or rather projectile) is the single most important component of accuracy. But testing of projectiles cannot commence until I have other reloading variables standardized (headstamp, OAL, powder, primer).

Thanks for all of the effort you put into your Mythbuster threads! We all love them and they make us think!!!

Yes. Thanks for these mythbuster threads. I learn from them.

Hopefully they provide more thought provoking stimuli to produce more accurate loads instead of debates about color of press.

But what about lubing the cases. That puts less stress/flex in much the same way does it not? Would that not be equivalent to pre-resizing? What if one did both?? AAHH, where does it end?

Since not all the reloaders lube their pistol brass, I wasn't going to include lube testing. However, I did pick up a can of One Shot to test whether residual lube inside case neck will affect neck tension/bullet setback. I am figuring out a "standardized" method to evenly apply lube inside the case neck for testing.

 

[Blue68f100]

OK. Test was done with RMR 124 gr FMJ FP bullets.

Test procedure:

• BLAZER 9mm brass were resized and they ranged from .749" to .752".
• Five cases measuring .750" were selected
• Rocky Mountain Reloading In-House 124 gr FMJ FP
• Test rounds were loaded on Pro 1000 using Lee dies
• Frankford Arsenal dial calipers verified with Vermont pin gages

Regular Reloading - Bullets were seated with all 3 stations full. OAL/COL sorted from shortest to longest:

1. 1.070"
2. 1.070"
3. 1.071"
4. 1.071"
5. 1.072"

Pre-Resized Brass Reloading - Resizing/depriming die removed from Station 1. All bullets were seated while flaring a case in Station 2. OAL/COL sorted from shortest to longest:

1. 1.069"
2. 1.069"
3. 1.070"
4. 1.070"
   
5. 1.070"

Summary - Using same BLAZER headstamp brass produced .002" OAL variance while using pre-resized brass produced 001" OAL variance

Did you use a Flat seating stem or the one for RN?

 

[LiveLife]

One for RN.

Lee seating/crimping die only comes with one bullet seating stem.

But since the stem contacts the tip of FP, OAL measurement should be actual unlike RN which contacts slightly below the tip.

 

[Doublehelix]

@bds you are the man!!!

Your mythbuster threads are the best reads on the internet, next of course to your contributions to the "draw and reloading" thread over in the Competition Shooting forum, which is just a gold mine of information!!! Love it! Best thread on THR at the moment!!!

Like you said, you can present the information, (and I agree that you have shown that there is a pattern that shows more COAL variation when you do not pre-resize), and then it is up to us to decide if we want to follow the advice that the conclusions lead us to.

For this particular Myth to change my behavior, since it is a lot more more work (!), I would have to see results at the target end, not just the caliper end.

Did you have a chance to shoot these cartridges that you made for these tests and compare the accuracy?

A few other comments:

1. You mention that @jmorris talks about needing 10 rounds to be the minimally statistically significant number of rounds for accuracy testing, but I think that also would apply with your Mythbusting COAL test. 5 rounds seems low to me as well.
2. I understand why you use mixed brass for some Mythbusting threads, but IMHO, this particular myth would be best served by removing that variable from the equation and using a single type of brass. If we truly want to know what effect the shell plate flex has on COAL, we need to make sure that there are no other variables affecting the results. Maybe we will have to start doing two sets, one with mixed brass for real world comparisons, and then one where you are looking to bust the myth with the most accurate data.
3. I think you would also need to measure and cull a set of bullets that have a consistent length. I am not sure how best to measure this (base-to-tip, base-to-ogive????), but we probably need to remove this variable from the mix as well.
4. As mentioned, I would love to see the accuracy difference of these different techniques in action. We can come to the conclusion that there is between a 1 and 2 thousands difference in COAL between techniques, but does that necessarily imply a difference on the target? If so, we need data!!! Since these are pistol rounds, I am not sure how far you would want to shoot them for testing, but certainly no more than 25 yards. For this test, you would need at least 10 rounds as mentioned earlier.

IMHO, the myth that really needs busting is whether or not the difference in COAL makes a difference in accuracy. Nobody really cares that they have some cartridges in their magazine that are 1/4 to 1/2 a hair's width longer than the others, but whether or not this difference affects accuracy. At least, this is what matters to me...

I think you have proven that there IS A DIFFERENCE, but now we need to know if that small difference really matters where it counts, at the target. If I am going to take the time to run my cases through the press twice, I want to make sure it is worth my time, not just for bragging rights to say all my finished cartridges are within .001" COAL. For example, about 6 months ago or so, I stopped priming by hand because it was taking too long, and honestly, I could not see enough of a difference at the target end to make it worth the extra time and effort that was involved. That is just me I realize. YMMV.

(Don't you love how my suggestions always involve MORE WORK on your part!!! Hehe... sorry about that!!! Maybe we can get that no good, lazy, shiftless, do nothing @Walkalong to help out!!! LOL!!! Just kidding... )

Thanks again for all you do. This is really awesome!

 

[jmorris]

Got me by the @jmorris part, yeah one has to watch sample size, for shell plate deflection, some presses have the cases sit “in” the shell plate others have them sit on the platform and the shell plate just contacts them in the extractor grove.

Lots of variables in this one though, brass, dies, press, bullets, would be neat to see difference with maybe OAL measurements and ogive measurements where the seater contacts the bullet.

 

[LiveLife]

But what about lubing the cases.

Don't you love how my suggestions always involve MORE WORK on your part!!!

I did pick up a can of One Shot to test whether residual lube inside case neck will affect neck tension/bullet setback.

Ask and you shall receive.

This myth busting thread demonstrated residual lube (wet and dry) left by One Shot did not produce bullet setback - https://www.thehighroad.org/index.p...affect-on-neck-tension-bullet-setback.834035/