Bolt Action Loading: Is Purpose Of Min Shoulder Bump Accuracy and/or Brass Life?

[otisrush]

The gun being loaded for is a Rem 700 in .243 Win. I will be using a FL sizing die to bump the shoulder back of fired brass a few thousandths.

After testing some loads in brand new Nosler brass (and finding some loads that performed REALLY well) it made me wonder if I was now going to have to re-go-through the load development process now that I have brass that is fireformed to my chamber.

So - when people here have talked of the benefits of doing minimal sizing after firing, is the root objective to maximize brass life? Or is there an expectation that accuracy can be improved with fireformed brass that gets a minimal shoulder bump? If an expectation is improved accuracy, that potentially tells me I may want to go through the load development process again with the fireformed brass?

Thanks.

OR

 

[dgod]

First, 243 is a great round, I have loaded it for years. The posts have to do with Maximizing Brass/Case life. I have always used full length resizing, I also trim to spec after each resize. But that is just me. And to that I say "To each his own"..

What bullet are you planning to use? BTW, .243 and 6mm are the same bullets. This is one of the few that I do not cast, mainly because most of the loads are pretty quick and would require Gas Checks.

Good Caliber, fun to shoot, devastating on the other end.

Good Luck
Dan

 

[otisrush]

First, 243 is a great round, I have loaded it for years. The posts have to do with Maximizing Brass/Case life. I have always used full length resizing, I also trim to spec after each resize. But that is just me. And to that I say "To each his own"..

What bullet are you planning to use? BTW, .243 and 6mm are the same bullets. This is one of the few that I do not cast, mainly because most of the loads are pretty quick and would require Gas Checks.

Good Caliber, fun to shoot, devastating on the other end.

Good Luck
Dan

I love the .243 as well. I just got this gun a few months ago. (My first in .243) I'm pretty much at the end of getting it configured how I want. It's a Rem 700 Varmint config - 26" bull barrel. I put a Leupold 4-14x scope on it, a Timney Calvin Elite trigger, and a Boyd's thumbhole varmint stock. I'm not hunting with it. Just want to do some semi-serious paper punching as well as ringing steel up to 500 yds out.

I'm using the Hornady Match 105gr HP BT bullet. A few days ago I tested some loads using H1000 for the first time. Out of four loads one was very very bad. But the other three were all really good. The best delivered a 3 shot group at .33 MOA. :-D

Those first loads were at the low end of the load data. I hope I can find a load that groups as well as what I've done so far but push the muzzle velocity up a bit.

OR

 

[dgod]

I have had good luck with IMR-4064 and IMR-3031.

I just checked my Chrony files, and I have not checked any 243 loads, wow... I'll have to correct that oversight..

 

[Slamfire]

So - when people here have talked of the benefits of doing minimal sizing after firing, is the root objective to maximize brass life? Or is there an expectation that accuracy can be improved with fireformed brass that gets a minimal shoulder bump? If an expectation is improved accuracy, that potentially tells me I may want to go through the load development process again with the fireformed brass?

I am of the opinion that the idea that tight chambers produce more accurate results is a flawed idea that goes way, way back. I remember reading references to tight Neidner chambers in pre WW2 literature.

The basic problem is proving that tight chambers means better accuracy. And then, how tight. Assuming that bench rest shooters are using tight chambers and cases one should not over look their rifles are single shot, very heavy, and may or may not have an ejector. This rifle set some 1000 yard World record, but it is a crew served weapon and requires a concrete table for a platform.




For normal, hand held weapons, I think the tight chamber idea is a bad idea. My rifles with ammunition that is sized less than the chamber feed well, extract well, and are more accurate (at least the match ones) than my hold. I have recently run into problems with one 308 Winchester match rifle of mine and cases that were full length resized in a Lee Die. The cases had the proper base to shoulder distance, but the Lee Die left them fat. Those cases would stick in my rifle and I had to knock the cases out with a cleaning rod.

175 SMK 40.5 grs AA4064, wtd, lot 2398 Czech, LC 79 WLR OAL 2.800"                                  

                                                                                                                                             

23-Jan-17                       T = 55 °F                                                                                          

                                                                                                                                             

Ave Vel =                       2486                               2496            2498                                      

Std Dev =                      16                                   2459            2459                                      

ES =                              47                                   2495            2488                                      

Low =                            2459                                2489            2487                                      

High =                            2506                                2487            2506                                      

N =                                10                                                                                                    

                                                                                                                                             

Stuck case shots 3 & 7. Hard to close bolt, had to use cleaning rod to extract case                 

Nice rounded primers                                                                                                             

                                                                                                                                             

175 SMK 41.0 grs AA4064, wtd, lot 2398 Czech, LC 79 WLR OAL 2.800"                                  

                                                                                                                                             

23-Jan-17                       T = 55 °F                                                                                          

                                                                                                                                             

Ave Vel =                       2527                               2523            2503                                      

Std Dev =                      23                                   2497            2544                                      

ES =                              64                                   2537            2521                                      

Low =                            2497                                2558            2561                                      

High =                            2561                                2503            2522                                      

N =                                10                                                                                                    

                                                                                                                                             

Stuck case shots 6 & 8. Hard to close bolt, had to use cleaning rod to extract case                 

rounded primers

I resized every case in that ammunition box with a small base sizer, verified that all were sized to gage minimum, (for that chamber), loaded enough cases up with the above loads, and took them to a rifle match. Everything feed and extracted without incident. Whatever accuracy improvement there might be to tight cases, and as I have written, this is un-quantified, there is a reliability penalty for having stuck cases.


Generally speaking, full length resize and bump the shoulders back 0.003". You want the case to be smaller than the chamber, but only a little bit, as you don't want excessive sidewall stretch.

 

[Bart B.]

My root objective is two-fold; best accuracy and long case life.

I see little, if any difference in new case versus proper full length sized ones

The 243 and its brethren in 26, 28, 30 and 35 caliber versions of the same case body all fit chambers the same way when fired. The firing pin drives them a few thousandths forward in the chamber if an in-line ejector isn't already pushing it there. The case shoulder centers perfectly in the chamber shoulder then that pin dents the primer firing the round.

As the case neck and bullet are also centered in the chamber (if the cartridge is straight), the bullet starts very straight into the rifling. Meanwhile, the case body is centered in the front part of the chamber and doesn't touch the chamber wall anywhere. The back end of the case is pressed against the chamber wall a little bit in front of the extractor groove so the back of the case is a thousandth or more off center; nothing wrong with that. That point is the only place the case body touches the chambers wall. For every .001" the case head is off center in the back of the chamber, the bullet tip will be .0005" off center the opposite direction in the bore. Not a problem and it's typically very repeatable from shot to shot.

As pressure builds, the case expands to chamber limits then shrinks back a little. Full length sizing that case shrinks it back down. All cartridges based on the 308 case can be reloaded 50 or more times is minimally sized. Full length dies keep the case neck aligned with the case body so bullets seated in them are straighter when they start into the rifling. Neck sizing dies don't do that; they let the case body flop around too much.

By now, you should realize that a 243 Win bullet will perfectly center in a 308 Win chamber when fired. Centering of case neck and bullet is due to matching case and chamber shoulders. Not by tight chamber necks that so many think is why. Yes, there would be a lot of clearance around the 243 case neck in a 308 chamber, but it's uniform all the way around. Normally, there's only a few thousandths clearance.

The difference between new and fired/resized cases is about .001" more clearance between case body and chamber; no big deal whatsoever. They both center bullets in the bore equally precise.

Get a set of Redding Competition Shell Holders then use the one that bumps case shoulders back .001" to .002" when it's hard against the sizing die bottom. There's 5 in .002" increments in height above case head platform. You'll need a case headspace gauge of some type to measure cases. RCBS Precision Mic, Hornady LNL or a nylon bushing to use with your calipers. See post 9 in:

https://www.thehighroad.org/index.php?threads/headspace.815278/

For load data

http://www.6mmbr.com/243win.html

 

[kingmt]

The gun being loaded for is a Rem 700 in .243 Win. I will be using a FL sizing die to bump the shoulder back of fired brass a few thousandths.

After testing some loads in brand new Nosler brass (and finding some loads that performed REALLY well) it made me wonder if I was now going to have to re-go-through the load development process now that I have brass that is fireformed to my chamber.

So - when people here have talked of the benefits of doing minimal sizing after firing, is the root objective to maximize brass life? Or is there an expectation that accuracy can be improved with fireformed brass that gets a minimal shoulder bump? If an expectation is improved accuracy, that potentially tells me I may want to go through the load development process again with the fireformed brass?

Thanks.

OR

Congrats on the new rifle. I'm a 243 fan myself. I was wondering at what yardage those groups were shot.

I usually neck size most of my bolt rifle rounds. I do this manly because it's easier. I think the brass last longer also but I haven't actually done any testing to even prove this to myself. My groups are smaller with neck sized brass but not really enough to make it worth while if that was my only purpose. I have had a couple of stuck cases from neck only sizing.

Edited to fix typos.

 

[Bart B.]

It's easy to get 40 to 50 reloads per case full length sizing the right way. Sometimes more. All with normal, maximum, safe reloads.

The benchrest discipline finally learned that full length sizing produces better accuracy and precision several years ago. Their smallest groups stayed the same size. Biggest ones shrunk down. Averages were smaller. Sierra bullets proved this in the late 1950's.

 

[quartermaster]

I believe accuracy can be improved by just setting the shoulders back .002. It would seem to me that the case would be more centered in the chamber making concentricity better. I also do prefer a tight neck chamber, even though kind of impossible to get in a factory rifle. I always turn my necks, even in rifles without tight neck chambers as I believe bullet release is more uniform.

I have bushing dies to adjust my neck tension, which leads to why my procedure is what it is. My resizing stage consists of taking the expander out of the FL die and setting the shoulder back and then neck sizing with a bushing to attain desired neck tension.

I have seen a large variation between fired cases and those full length sized. All depends on the reamer used. I do anneal all my cases after 3 firings to get the neck tensions the same, sometimes after 2 firings. I'm sure this does help case life, but I have always found that primer pocket loosening will be the reason cases are discarded before the case weakens from over sizing or in most cases neck splitting.

Case life is important especially when using premium brass, so anything we can do to prolong it's life is healthy for our wallets. There are certainly lots of different thoughts on how to go through the reloading procees and each of us has to do what works best for us and gives us the most confidence in our loads

 

[Offfhand]

The benchrest discipline finally learned that full length sizing produces better accuracy and precision several years ago. Their smallest groups stayed the same size. Biggest ones shrunk down. Averages were smaller. Sierra bullets proved this in the late 1950's

This is one of those comical fallacies often repeated by posters who don’t understand the sophisticated reloading techniques employed by elite benchrest shooters. First of all, they don’t-actually can’t- full length resize cases because they typically fire cartridges to which there is no specific dimension to resize to, as with standard calibers. Typically, a fired case is selectively sized to match an individual chamber. With a popular BR cartridge such as the 6PPC there will be dozens of nominally PPC rifles on the line but with widely varying chamber dimensions, none of which would conform to any prescribed “Full Length” resizeing dimension. Which is why benchrest shooters use specialized sizing dies that address specific dimensions of the fired case and, of notable importance, may alter the degree and area of case sizing during the course of a tournament. Recently, these advanced techniques have been borrowed from the benchrest game and applied to other shooting disciplines, which helps explain the improved scores seen in recent times.

 

[Bart B.]

First of all, they don’t-actually can’t- full length resize cases because they typically fire cartridges to which there is no specific dimension to resize to, as with standard calibers.

That's news to me.

I don't know, nor ever heard of, any specific dimension a fired case needs to be resized to in order the process be called "full length sizing." As long as the case dimensions from pressure ring forward are reduced any amount, it's full length sized.

If some fired cases have areas forward of that pressure ring whose dimension is not reduced, then it's partial full length sizing. Excepting neck only methods. According to several reloading die makers I discussed this with.

 

[Walkalong]

That's just the axe Bart likes to grind about Benchresters. His mind is made up and there ain't no use debating it with him. Sierra never loaded like Benchrest does, or did, so they never really proved anything other than full length sizing gave them better accuracy that neck sizing with big samples. There is much more going on with sizing for a 6 PPC Benchrest rifle than just neck vs full sizing etc for a standard chamber. I've given up debating it.

 

[Walkalong]

I am of the opinion that the idea that tight chambers produce more accurate results is a flawed idea that goes way, way back.

The chamber needs to be concentric and aligned with the bore. After that the min or max is largely a moot point. Brass fit is something worth talking about, and if the chamber is too sloppy, that ain't good, which I am sure where "tight" chambers started getting touted. After being concentric and aligned with the bore, after that it just can't be sloppy big.

IMHO of course.

 

[Bart B.]

Here's something the tight-chamber-neck folks might want to think about.

Why does a perfectly straight 243 Win round perfectly center its bullet in a perfectly straight 308 Win chamber should it be fired? Even when it's case body diameter is .004" smaller than the chamber body.

Sierra never loaded like Benchrest does, or did, so they never really proved anything other than full length sizing gave them better accuracy that neck sizing with big samples

They did when Ferris Pindel worked in their tool and die shop. He's one along with Arvin Martin who helped Jim Hull figure out full length sizing with standard dies made their best match bullets shoot in the ones and zeros in their 100 yard range.

 

[Walkalong]

Out of curiosity, what year was that? And was it with standard chambers or tight necked custom chambers with all the prep Benchresters do?

 

[243winxb]

After testing some loads in brand new Nosler brass (and finding some loads that performed REALLY well) it made me wonder if I was now going to have to re-go-through the load development process now that I have brass that is fireformed to my chamber.

Military testing of new 5.56 ammo , compared to fired, shows the fired brass (neck sized) will have 4% more volume.

For the 243 win, i would guess even more.

 

[243winxb]

when people here have talked of the benefits of doing minimal sizing after firing, is the root objective to maximize brass life? Or is there an expectation that accuracy can be improved with fireformed brass that gets a minimal shoulder bump? If an expectation is improved accuracy, that potentially tells me I may want to go through the load development process again with the fireformed brass?

Standard RCBS dies - FL is more accurate than neck sizing.

A Redding FL type S bushing die is best for case life and accuracy, less working of the neck area, while controlling shoulder bump.

Neck turning seems to help Win brass for me, along with full benchrest prep of the brass.

Doing your own testing is the only way to know.

 

[243winxb]

I see little, if any difference in new case versus proper full length sized ones

The difference is 1/4" @100 yds using Win brass right out of the bag, compared to fully prepped brass. Really not worth the trouble, unless trying for the smallest groups.

 

[RugerBassMan]

Usually, I buy used or once fired brass. I F/L resize this stuff so I get a very minimum headspace, just enough to feel a slight resistance upon closing the bolt (minus firing pin, spring, & cocking piece). To me "bumping" brass is like squashing brass, be real careful not to create excessive head space. Decades ago when I was an aspiring young hi-power shooter I appreciated the feel of properly sized slick feeding brass sliding into the chamber with little or no resistance which resulted in minimal movement (bolt working jiggling) of the rifle during rapid fire events - I F/L sized all ammo.

Some brass bumping that I do:

Making .20 Practical cases out of once fired .223's (cheap large volumes of cheap brass) use of a small base .223 die to restore the brass to or close to SAAMI specs. Some of this stuff sticks in my chamber of not small based resized and often the head-space is insufficient.

Getting a variety of 6mm Rem, .257 R +P, and 7mmX57 to fit in my 6mm Ackley Improved chamber after reducing the neck to 6mm. The specs for the reamer that cut the chamber show a .001 short length between base to junction of neck and shoulder and that should be enough to achieve a "crush fit" upon closing the bolt; not so, at least that reamer was not used. I could not close the bolt on these cases, 6mm Rem, .257 R+P and 7X57. The solution was to grind down a shell holder to allow another .003 inches of case travel into the die; then they all fit in allowing fire forming with cream of wheat (COW method).

Generally, all aspects have to be considered like the size of the chamber, with the goal of achieving optimum head space to allow smooth feeding of ammo. Amazingly, I have achieved spectacular accuracy from ammo that I thought had excessive head space. Continue to compress or bump shoulders back then fire with generous head space and head separations will happen - the cartridge comes apart some 1/2 inch from the base.

The .243 loaded with 87 Hornady VMax's at about 3200 fps is beautiful.

 

[WestKentucky]

Case life. Accuracy is all about load working to find a sweet spot, then the consistency to keep your load at that tiny spot where it shoots nicely.

 

[Bart B.]

In response to my post #14:

Out of curiosity, what year was that? And was it with standard chambers or tight necked custom chambers with all the prep Benchresters do?

The mid to late 1950's, if my memory's good. That's when Sierra started fooling around with hollow point 30 caliber match bullets and their first (the 168 Int'l Match) shot so well. Pindel chambered one of his benchrest riles with a .308 Win barrel to shoot them and won his next match. Hull had championed the use of SAAMI spec chambers and unprepped good cases full length sized with standard dies that Arvie Martin had honed their necks out to size fired cases just enough to hold bullets reliably. Good lots jacket material enabled bullets made to shoot in the 2's on average.

. I F/L resize this stuff so I get a very minimum headspace, just enough to feel a slight resistance upon closing the bolt (minus firing pin, spring, & cocking piece). To me "bumping" brass is like squashing brass, be real careful not to create excessive head space.

This is one thing Sierra's ballistic test man also proved to degrade accuracy. Benchrest folks at the time were neck only sizing cases but after 4 or 5 reloads, the case headspace (distance from case head to shoulder reference diameter) grew enough to be a tight fit in the chamber when head clearance (space between bolt face and case head when fired)was zero or a bit less. That bound the bolt when it closed into battery but not at the exact same place every time. That changed the mating position of bolt lug to receiver boss changing the way the bolt set back from chamber pressure. Groups with ammo that shot in the 2's with enough head clearance to let the bolt go into battery exactly the same for each shot now shot in the 4's and sometimes 5's. Only a tenth or two MOA bigger, but it was time to full length size the case setting the shoulder back a couple thousandths so head clearance was .001" or more to let the bolt close into battery exactly the same for each shot. It was worse when bolt faces were not squared up with the chamber axis. Some of the earliest case headspace measuring gauges made came out of Sierra Bullets' tool and die shop so Martin Hull could full length size the bottleneck cases used to test their bullets would be minimally sized and produce best accuracy and case life.

Martin Hull was well known for his remark that the "case must fit the chamber like a t*rd in a violin case." Enough clearance to the chamber so nothing bound up when the bolt closed. Reducing all the case diameters forward of the pressure ring and setting the shoulder back a thousandth or two ensured any mix of out of round case to out of round chamber would not bind up the case when chambered in any way.

Nowadays, some people have a custom full length sizing die made for their fired cases to size down all over a thousandth inch or less. Just enough to prevent the bolt from binding and keep the case head square after every firing. These dies keep the case body well aligned with the case shoulder and case neck so the cases come out as straight as possible.

Their necks touch no part of the chamber neck when fired; necks are centered in the chamber by the case shoulder perfectly fitting the chamber shoulder and its well centered on the case shoulder. Tight chamber necks limit the amount case necks expand therefore lessening their work hardening and increasing case life. The only way a chamber neck can center a case neck in it is to have the same diameter. Not a good idea.

One important difference between benchrest winning and record setting groups. Commercial bullets from Barnes, Berger, Hornady, Lapua, Sierra and others rarely product those results through 300 yards. Custom bullets are the norm; they're listed in:

http://benchrest.com/attachment.php?attachmentid=17880&d=1464811628

From what I've gleaned, customs shoot about 1/10th MOA better through 300 yards.

 

[hdwhit]

otisrush wrote:
Bolt Action Loading: Is Purpose Of Min Shoulder Bump Accuracy and/or Brass Life?

In my particular situation, it is a question of getting the brass sized to the point where it can be chambered without breaking the handle on the bolt. Bolt action rifles should not be called-upon to use the bolt handle as a surrogate for the lever on a reloading press.

If your current dies will not re-size for cases coming out of your bolt-gun, then either:
Segregate your brass based on the gun it was fired in and size/neck-size accordingly.
Re-size everything to work in the tightest chamber you have an accept a reduced life from the brass (i.e. 3 to 5 rr-;loads versus 7 to 12 loads at the lower-end.

 

[Bart B.]

One could mark the full length sizing die's lock ring to a reference on the die threads then set it in the press for what's needed to size fired cases correctly for different chambers. A 1/13" change in the lock ring circumference reference (about 1/36th turn) around the die threads moves it .002" up or down in the press when snugged in tight.

Read post #6 in this thread.

 

[otisrush]

Thanks for all the info. Just to follow up and so y'all don't think I "checked out" on this thread, I'll add a couple of things......

First, the info above is great. I've learned a ton.

What started this thread was what resulted after I loaded up some brand new Nosler brass:
44.5gr H1000
105 gr Hornady Match Bullet
This is coming out of 26" 9 1/8" twist barrel

The results significantly exceeded my expectations. This load produced a 3-shot group at .33 MOA. (My point in reporting this is that I'm not looking to shrink that group. I'm very happy with that result given what I"m trying to do - which is plink steel at the 300 and higher yd distance.)

I will be using a FL die to bump the shoulder of the now-fired cases back probably .002"-.003". (I have the Hornady multi-bushing headspace gauge set to help me monitor this.)

Question #1: Since the case volume will presumably change at least some between the original new brass (that produced the above results) and the now fired-but-shoulder-has-been-moved-back-a-few-thousandths, will that same above load produce essentially the same results? Or do I need to REstart my load development because these now slightly-sized cases have a different volume? (I think I'm concluding the above load will essentially perform the same, new brass vs slightly FL resized brass. Although there is greater case volume, the change in results will be negligible.)

Question #2: If accuracy doesn't basically change between new and slightly-FL-resized brass, then why are people fixated on doing only a small shoulder bump? What I'm concluding for this question the answer is case life. The less the brass is worked the longer it lasts - both from a work hardening perspective but mostly from the fact that less needs to be trimmed/removed less frequently.

If I'm off base in the above please let me know.

Thx again!

OR

 

[Bart B.]

Case volume won't change more than about 0.123% with a .002" change in shoulder location, which is minuscule and insignificant. Maybe about the same pressure difference a 1/20th grain in charge weight causes. It's always the same volume at peak pressure. I've shot the same load in new cases and after they're resized setting shoulders back .002" and shot them with the same sight settings at long range. If any pressure difference happened, it caused less than a 1/4th MOA sight change.

Minimal shoulder bump minimizes case stretching and increases case life. It also keeps case heads square which also helps keep groups small.

Hope that load shoots all its 3-shot groups under .500". Shoot a few more to verify. You're not off base except if you're going around them from hitting a home run with that great group.