Recommended headspace for FL sizing AR brass

[highxj]

Hey guys, I'm coming from the world of precision bench and varmint rifle handloading and have a question about FL sizing brass for my AR.

I generally neck size using custom bushing dies, or FL size when necessary to bump the shoulder back about .0015" on my fired cases for my bolt guns. I understand that the AR platform is a different animal and requires FL sizing with a shoulder bump each time.....my question is, how much is enough to insure reliability over hundreds of rounds between cleanings? I use (and love) Redding Competition shell holders, so I can precisely and easily adjust the shoulder position during sizing. My thought is to bump the shoulder back .002" on a fired case, but I'm wondering if .004" might not be a better idea and may be a little more forgiving when things start to get dirty.

Thoughts?

[Corey]

Bump it back .003-.005 and you'll be good. It needs a bit more than a standard bolt gun.

[highxj]

Probably a good plan, I'll stick with the Redding +.006" shell holder which moves my shoulder back .004".

A few months ago, I sent off a batch of once fired 5.56 brass to a fella in Texas for processing. It came back looking great, but unfortunately he bumped them back a full .010" . I emailed him and told him he may want to consider adjusting his tooling as he was a full .006" shorter than an unfired W-W case and he was basically ruining brass, but he didn't want to hear about it. I am shooting them....but I measure each one afterwards. About one in five stretch, so they get tossed.

If you want something done right...........ya' know.

Bump it back .003-.005 and you'll be good. It needs a bit more than a standard bolt gun.

[jaredr]

you mentioned you use redding competition shellholders, so I gather you're loading on a single-stage press? if you're getting into AR's for competition or even just casual plinking, you may get really tired of doing all of your brass prep and loading on a single stage press. folks who reload .223 in volume generally use a progressive press and keep two separate toolheads - one for depriming, resizing, trimming, and another for priming, powder drop, bullet seating and crimping. goes without saying that one of the benefits of processing your own brass is you get to control your resizing specs

[highxj]

Jared, I have a couple of progressives but I'm thinking I'll FL size everything on a single stage then run them through the Dillon.

One reason is so I *can* carefully control headspace.

[RH45]

Probably a good plan, I'll stick with the Redding +.006" shell holder which moves my shoulder back .004".

A few months ago, I sent off a batch of once fired 5.56 brass to a fella in Texas for processing. It came back looking great, but unfortunately he bumped them back a full .010" . I emailed him and told him he may want to consider adjusting his tooling as he was a full .006" shorter than an unfired W-W case and he was basically ruining brass, but he didn't want to hear about it. I am shooting them....but I measure each one afterwards. About one in five stretch, so they get tossed.

If you want something done right...........ya' know.

I hope it was a different guy in Texas than I sent my .308 brass to. When my .308 brass came back, it measured perfectly to factory specs, in every way!

Edited March 27, 2011 by RH45

[Warhammer4k]

OP, how are you measuring headspace?

I use a Stoney Point headspace gage. It is pretty much the same as the current Hornady Lock-n-Load Headspace Gage (Hornady bought out Stoney Point some time ago).

I also have the Bullet Comparator/COAL tool for determining optimum bullet seating depth for any given rifle. I'm sure that since you already shoot benchrest you have something similar or have determined these numbers in some other way.

Anyway, I've been sizing my brass to bump the shoulder back to where it is on new factory ammo. It's probably a little more than necessary, because I don't have any way to measure the headspace that the rifle actually requires. Determining the latter is done with something like the RCBS Precision Mic Headspace Tool. But, since I shoot bone stock guns with "military" style 5.56 chambers, I feel it's best to duplicate the geometry of "military" ammo as closely as possible.

If I'm indeed bumping back the shoulders too much, I guess I'll wear out my brass sooner. Not sure how long it's going to last anyway, given that I'm FL sizing (all my .223 guns are semiautos) and using the RCBS small-base X-die for sizing. Been wondering whether the small-base thing was a stupid idea. I chose it because I figured it would guarantee feeding, but possibly SB dies are just useless and unnecessary in general.

[Powder Finger]

OP, how are you measuring headspace?

I use a Stoney Point headspace gage. It is pretty much the same as the current Hornady Lock-n-Load Headspace Gage (Hornady bought out Stoney Point some time ago).

I also have the Bullet Comparator/COAL tool for determining optimum bullet seating depth for any given rifle. I'm sure that since you already shoot benchrest you have something similar or have determined these numbers in some other way.

Anyway, I've been sizing my brass to bump the shoulder back to where it is on new factory ammo. It's probably a little more than necessary, because I don't have any way to measure the headspace that the rifle actually requires. Determining the latter is done with something like the RCBS Precision Mic Headspace Tool. But, since I shoot bone stock guns with "military" style 5.56 chambers, I feel it's best to duplicate the geometry of "military" ammo as closely as possible.

If I'm indeed bumping back the shoulders too much, I guess I'll wear out my brass sooner. Not sure how long it's going to last anyway, given that I'm FL sizing (all my .223 guns are semiautos) and using the RCBS small-base X-die for sizing. Been wondering whether the small-base thing was a stupid idea. I chose it because I figured it would guarantee feeding, but possibly SB dies are just useless and unnecessary in general.

I think one way is to take a case, get rid of the primer, remove ejector. Then put tape on the back of the case until the bolt just closes. Then measure from taped head of the case to the shoulder to get that rifles number.

[Warhammer4k]

I just spent some time w/the headspace measuring tool and Lake City brass in various conditions.

Remember that the bushing on my tool measures to a somewhat arbitrary datum point on the case shoulder. So my measurements may vary from yours, but the differences in headspace are not dependent on my method of measurement.

Unfired M855 round headspace = 2.535"

Once-fired LC brass = 2.542"

Sized LC brass = 2.532"

Twice-fired LC brass = 2.539"

That's from just measuring one of each case. I'm sure there would be some variation if I measured samples, e.g. 10 of each. But it does look like my brass stretches a bit on the second firing.

Could be I'm sizing too much. I don't expect the brass to last forever, but I also don't want to wear it out prematurely.

I haven't had to think about annealing or case neck thickening yet, because I've yet to reload all my brass for the first time.

[Powder Finger]

I just spent some time w/the headspace measuring tool and Lake City brass in various conditions.

Remember that the bushing on my tool measures to a somewhat arbitrary datum point on the case shoulder. So my measurements may vary from yours, but the differences in headspace are not dependent on my method of measurement.

Unfired M855 round headspace = 2.535"

Once-fired LC brass = 2.542"Sized LC brass = 2.532"Twice-fired LC brass = 2.539"

That's from just measuring one of each case. I'm sure there would be some variation if I measured samples, e.g. 10 of each. But it does look like my brass stretches a bit on the second firing.

Could be I'm sizing too much. I don't expect the brass to last forever, but I also don't want to wear it out prematurely.

I haven't had to think about annealing or case neck thickening yet, because I've yet to reload all my brass for the first time.

That's 0.01 sizing off your once fired dimension I don't think you need more that .005 in a gas gun.

Also even if the case formed completely to your chamber (probably didn't) you still have .001 appx spring back on the case.

So if you have .001 spring back + .001 short of chamber any way now you size .01 you end up with about 0.012 clearance.

[Warhammer4k]

Fortunately, the amount of sizing is easy to remedy on the next reloading cycle.

[highxj]

Warhammer4k yes I'm using the Stoney Point headspace measuring tool. In my experience, with full power loads, the measurement of the fired case will be approximately a thousandth or perhaps .0015" shorter than actual chamber dimension. Generally anyway, and this is with small varmint cases. Repeatedly firing the neck sized case will eventually result in it being 'snug' to chamber. These cases are 'about' .001" to .0015" longer in body length than the once fired case was.

As far as the SB sizing die goes, I don't use one and with my current chamber don't seem to need it. My cases are being sized about .0014" ahead of the web and they feed and chamber freely, so I'm not going to unnecessarily work my cases if I don't have to.

Anyway....thanks for confirming my sizing procedure on the 5.56 gas gun. I think I'm good to go now

[Warhammer4k]

I ran another batch through the size die today. This time, I adjusted things so that I was only pushing the case shoulder back 0.005".

That should help brass life in the long run.

It will be a while before brass life is an issue, however. I have 1000 Remington .223 Rem cases and over 1000 Lake City pieces to work with. I still have hundreds of both that have yet to be reloaded.