Setting head space on an AR pointless?

[Tangodown911]

So I'm loading up some match ammo for a new AR platform... .223. Take some headspace measurements from once fired brass from the new rifle. I start full length sizing the brass and bumping the shoulder .002" back. It's set up to be a precision rig so I figure .002" is just right while still keeping reliability up also. I measure a few pieces of f/L brass bumped back as mentioned then decide to chamber a few pieces of brass to check for extraction and chambering. I then measured the brass again and found the shoulders on all the brass had been pushed back an additional .007" which means its more .009" under the once fired brass.

My two cents: I chamber the brass by pushing them into the chamber by hand them allowing the bolt to slam forward just is it would when naturally chambering a round or during firing. I suppose the shoulder is being pushed back by the extractor pushing the brass onto the chamber just before the extractor claw jumps over the rims of the case.

Needless to say, I started thinking if i was wasting my time with trying to be precise with headspace on an AR platform. Am I missing something here or is this S.O.P. on an AR?

 

[erik72]

Re: Setting head space on an AR pointless?

I'm very curious about this as well. I've read elsewhere that full length resizing is all that is required but the more I read on these boards and others, it seems to be a critical step. Maybe its exclusive to bolt guns...not sure. Is there a special die required to "bump" the shoulder back"? How is this process achieved?

 

[STI_1911_Guy]

Re: Setting head space on an AR pointless?

I also tried this to no avail in my dpms LR-260 and My DPMS 223. My 260 when pushed back .003 would not chamber reliably. The 223 would chamber but just from the chambering alone i would see variances in bullet runout and headspace after chambering the round. As i started to experiment more i found that the effects of only bumping the shoulder back .003 and how it was significantly harder to chamber was worse on accuracy than actually setting the FL sizing die down to touch the shellholder. My groups with my 260 have been as follows:

This seems to be the average with my 260 some are even a little better around .3-.4 if i do my part. WHile i havent done as much playing with my 223 i will say that i would not bother myself with trying to set the headspace on this. I will just FL size and that is what seems to work best for me.

 

[country888]

Re: Setting head space on an AR pointless?

Correct me if im wrong, but chambering a round should not push the sholder back. If it did, it shouldn't be more that 1 to 2 thousnads. Did you check all the brass before resizing it? I do set my headspace on my AR's but havnt run into this. What I have found is .001 to .003 difference in brass when checking headspace after being fired from my AR. I try to find a happy mediam and bump sholder back .004 from the middle measurement. Havn't ran into any problems doing this.

 

[Tangodown911]

Re: Setting head space on an AR pointless?

It shouldn't but apparently it does. I guess that's the difference in a bolt gun and a auto loader. I checked 20+ pieces of 1x fired brass to obtain my headspace measurement. And used the Hornady lnl gauge.

 

[jeff1383]

Re: Setting head space on an AR pointless?

Every piece of resized brass for my grendel goes through a Wilson case gauge...if it fits correctly, it fires.

 

[country888]

Re: Setting head space on an AR pointless?

I will check mine after chambering a few rounds & see what its doing. It may be seting it back some, but i have never noticed it. Its a good point tango. Something to check and think about!