Setting up dies for shoulder bump on .308 AR brass

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mikear

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Jan 22, 2011
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#1
First off, I haven't hand loaded a single round but am slowly receiving my equipment from the brown truck each day. I purchased a Forster FL die and was going to set it up to bump the shoulder approximately .003" on my fire formed brass (.308). I am using the Sinclair bump gauge to check my brass. Brass is Federal from Gold Medal Match commercial ammo.

The variance between rounds range from 1.562"-1.566". Where should I start? Bump the 1.566" to 1.563" (-.003") and just know the 1.562" brass won't get bumped and will eventually form to >1.563" and then be bumped back on the next sizing?

Note: I read the tutorials and did a search, only found one post that said to find average length between fire formed brass then bump .004" below that.

What do you all think?
 
#3
Re: Setting up dies for shoulder bump on .308 AR brass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mikear</div><div class="ubbcode-body">First off, I haven't hand loaded a single round but am slowly receiving my equipment from the brown truck each day. I purchased a Forster FL die and was going to set it up to bump the shoulder approximately .003" on my fire formed brass (.308). I am using the Sinclair bump gauge to check my brass. Brass is Federal from Gold Medal Match commercial ammo.

The variance between rounds range from 1.562"-1.566". Where should I start? Bump the 1.566" to 1.563" (-.003") and just know the 1.562" brass won't get bumped and will eventually form to >1.563" and then be bumped back on the next sizing?

Note: I read the tutorials and did a search, only found one post that said to find average length between fire formed brass then bump .004" below that.

What do you all think? </div></div>

.003"-.004" from fireformed brass is a good start. With the amount of work hardening that your particular cases have, that might just give you that variation you're seeing. Things aren't exact and perfectly uniform.

For a gas gun, you might just err on the side of caution and aim for the the shorter number.

Chris
 
#4
Re: Setting up dies for shoulder bump on .308 AR brass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChrisGarrett</div><div class="ubbcode-body">.003"-.004" from fireformed brass is a good start. With the amount of work hardening that your particular cases have, that might just give you that variation you're seeing. Things aren't exact and perfectly uniform.

For a gas gun, you might just err on the side of caution and aim for the the shorter number.

Chris </div></div>

Chris,
You're saying to bump the shoulder back more (.004") or bump the shoulder on the shortest piece of brass (1.562")?

Okie,
Thanks for the reply, I am trying to set up my FL die so I can FL resize.
 
#5
Re: Setting up dies for shoulder bump on .308 AR brass

I would be sure you are giving your shortest piece of fired brass (1.562") at least a kiss on the shoulder, .001"-.002". It's not worth getting a jammed case in your chamber, having to smack the butt stock on the ground to extract it.

I reload for an early production SR-25 and it beats Federal brass to death. I have installed a Tubbs carrier weight system (CWS) which has helped,but I only get 2-3 reloadings on the Federal brass. I do better with Remington,Winchester and Hornady brass though.

I also have a set of Forster "National Match" 308 Winchester dies. I do like the way you can adjust the expander ball to sit at the base of the neck in the up stroke and go through the neck at the top of the down stroke. It makes it easier going through the neck. Smoother than other die designs.
 
#6
Re: Setting up dies for shoulder bump on .308 AR brass

Just "bumping the shoulder" will not give good results in ARs in my experience. You must remember that headspace length is not the only dimension you have to worry about. The farther you push the case into your die, the DIAMETER of the case body is also reduced. It is the diameter that many times causes troubles from not full length resizing your brass. I full length re-size all my AR brass and I can rest assured it will fit all my ARs plus any other guns I happen to pick up.
This is just my opinion and it's worth exactly what you paid for it. I been at this 30 years though, and I found many of the little accuracy tricks for bolt guns simply don't work for autoloaders and when they DO work they don't make much, if any, noticeable difference. YMMV
 
#7
Re: Setting up dies for shoulder bump on .308 AR brass

I use a small base full length sizer die (RCBS) and set it up according to the book. Screw it down until it contacts the shell holder on the upstroke and then give it another 1/8" or so turn. Never have feeding problems, the ammunition I make is reasonably accurate and brass lasts a long time.
 
#8
Re: Setting up dies for shoulder bump on .308 AR brass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mikear</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChrisGarrett</div><div class="ubbcode-body">.003"-.004" from fireformed brass is a good start. With the amount of work hardening that your particular cases have, that might just give you that variation you're seeing. Things aren't exact and perfectly uniform.

For a gas gun, you might just err on the side of caution and aim for the the shorter number.

Chris </div></div>

Chris,
You're saying to bump the shoulder back more (.004") or bump the shoulder on the shortest piece of brass (1.562")?

Okie,
Thanks for the reply, I am trying to set up my FL die so I can FL resize. </div></div>

If you take 100 fired cases and they measure X, Y and Z, with X being the longest at 1.000, Y being .998 and the shortest...z, being .996", I would try and size the longest ones down to that .996" level, that would give you your safety margin of .004", or if you want .003", you'd size the longer ones down to .997", for a .003" margin.

Since the longest ones are going to be potential issues, you should address their lengths first and foremost.

As the other fellow mentions, you also need to squeeze that body down, but that happens when you bump the shoulders back anyhow and unless you have a tight match cut chamber AND you're loading up M-240 fired brass, shot through a sloppy, wide chamber, small base dies, which squeeze the case body more than standard dies, shouldn't be necessary.

Chris
 
#9
Re: Setting up dies for shoulder bump on .308 AR brass

Thanks for all the responses. My rifle is an LAR-8 carbine, factory chamber setup. I will measure some factory brass that I regularly shoot to ensure I am at least close to the dimensions (body diameter, etc) after resizing. If I can get in that ballpark and still only be bumping the shoulder .003"-.004" to preserve brass, then all the better.
 
#12
Re: Setting up dies for shoulder bump on .308 AR brass

For ARs....I FL size every time. I have gotten away with alternating FL then NS and so on. To be honest, the cycling just didn't feel silky smooth. If you've ever had an AR jam bad...its a real B of an problem.
 
#13
Re: Setting up dies for shoulder bump on .308 AR brass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: boltgunluvr</div><div class="ubbcode-body">For ARs....I FL size every time. I have gotten away with alternating FL then NS and so on. To be honest, the cycling just didn't feel silky smooth. If you've ever had an AR jam bad...its a real B of an problem. </div></div>

I think I may be confused on using the FL die. You're saying if I just bump the shoulder .003"-.004" that I'll not be FL sizing? FL sizing in an FL die maybe doesn't size the whole body if you don't hit the shell holder with the die? Sorry for the elementary misunderstanding. I need my manuals to come in so I can read up!
 
#14
Re: Setting up dies for shoulder bump on .308 AR brass

One thing for the newby:

As the diameter gets compressed in the FL die, the shoulder will become farther from the base {i.e. longer} (Murphy's law with respect to where brass goes while being sized.)

So, set up the FL die to push the sholder back 0.003-0.004, and run even shorter brass through the same regimen. If you measure each case as it comes out, do not be surprised when the short brass has lengthened while in the die.
 
#15
Re: Setting up dies for shoulder bump on .308 AR brass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MitchAlsup</div><div class="ubbcode-body">One thing for the newby:

As the diameter gets compressed in the FL die, the shoulder will become farther from the base {i.e. longer} (Murphy's law with respect to where brass goes while being sized.)

So, set up the FL die to push the sholder back 0.003-0.004, and run even shorter brass through the same regimen. If you measure each case as it comes out, do not be surprised when the short brass has lengthened while in the die. </div></div>

Makes sense. So the shoulder bump is adjustable while still obtaining a FL resize on the body, correct?
 
#17
Re: Setting up dies for shoulder bump on .308 AR brass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mikear</div><div class="ubbcode-body">I need my manuals to come in so I can read up! </div></div>

FL dies squish the brass back to factory specs. Small base full length sizer dies squish it a little bit more. The shell holder has to make contact with the die for it to work. Sometimes, you can get a FL die to squish the brass a bit more by 'camming over' (screw the die down a little more so that it makes harder contact with the shell holder) but not usually.

Simplest way I can put it.
 
#18
Re: Setting up dies for shoulder bump on .308 AR brass

If you do that with for example Dillon FL dies you will knock the shoulder back so far, the ctg. will not headspace at all - too short. The ctg. will either not fire or may cause a excess headspace condition that you have cause with an over sized case. Not cool. Case head separation imminent - unsafe! Not all make dies or shell holders are the same. One size does not fit all here. Get the right tools and measure your fired v. sized cases. Set your die to the measurement. As stated, some dies can hit the shoulder HARD, some not enough. You don't need to guess and are foolish if you do. You can measure with a dial caliper and a 40s&w case. It's not like it's hard. Takes maybe 5 mins.. Only use the same shell holder you set the die with from then on as different makes differ in specs..
 
#19
Re: Setting up dies for shoulder bump on .308 AR brass

Correct me if I'm wrong, but I was under the impression that "camming over" was a capability of the press, not the dies.

SBD's, as I understand it, are a tighter tolerance through the lower half of the die, supporting as well as swaging the base of the brass back into SAAMI spec.
 
#20
Re: Setting up dies for shoulder bump on .308 AR brass

Marine, you are correct. The real question is do you really need a SBD? The individual weapon will decide that - not a reloading forum.
 
#21
Re: Setting up dies for shoulder bump on .308 AR brass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kolkio</div><div class="ubbcode-body">If you do that with for example Dillon FL dies you will knock the shoulder back so far, the ctg. will not headspace at all - too short. The ctg. will either not fire or may cause a excess headspace condition that you have cause with an over sized case. Not cool. Case head separation imminent - unsafe! Not all make dies or shell holders are the same. One size does not fit all here. Get the right tools and measure your fired v. sized cases. Set your die to the measurement. As stated, some dies can hit the shoulder HARD, some not enough. You don't need to guess and are foolish if you do. You can measure with a dial caliper and a 40s&w case. It's not like it's hard. Takes maybe 5 mins.. Only use the same shell holder you set the die with from then on as different makes differ in specs..</div></div>

I resized a couple pieces of brass and it bumped the shoulder back .006" when adjusting all the way down to touch the shell holder. Once I get the chance, I'll be slowly backing the die off to achieve the .003"-.004" bump. I am measuring each piece of brass with the Sinclair bump gage. Certainly no guesswork here.
 
#22
Re: Setting up dies for shoulder bump on .308 AR brass

Just an update/question. I backed off the FL sizing die to obtain .004-.005" bump, but it still touches the shell holder with a little camming at the top of the stroke. The bumping variance is .004-.005" where it is set wheb sizing once fired FC brass.

My question is, how hard should it be to chamber/eject rounds by hand? By bumping the shoulder .003", it was fairly difficult to eject with the charging handle. The .005" rounds eject great and the .004" are slightly more difficult than .005" rounds.
 
#23
Re: Setting up dies for shoulder bump on .308 AR brass


From what you've explained, the -.004", .005" bump is the way to go. A little over camming is fine. I'm able to get enough bump with my standard Redding F/L dies for my SR-25. It has a tight chamber.

As long as you're able to extract the loaded round out of your chamber without having to smack the butt on the ground, you are good. Be sure you have a clean chamber when doing all of this chambering testing.


A good accessory die to have is the Redding small base body only die. It F/L sizes a case without touching the neck. It's good to use on tight chambers

http://www.grafs.com/retail/catalog/product/productId/15154
 
#24
Re: Setting up dies for shoulder bump on .308 AR brass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: FLIGHT762</div><div class="ubbcode-body">
From what you've explained, the -.004", .005" bump is the way to go. A little over camming is fine. I'm able to get enough bump with my standard Redding F/L dies for my SR-25. It has a tight chamber.

As long as you're able to extract the loaded round out of your chamber without having to smack the butt on the ground, you are good. Be sure you have a clean chamber when doing all of this chambering testing.


A good accessory die to have is the Redding small base body only die. It F/L sizes a case without touching the neck. It's good to use on tight chambers

http://www.grafs.com/retail/catalog/product/productId/15154</div></div>

Thanks for the response. I'll load some of these up and see how they function.
 
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