Headspace for an AR10-T?

[Jumper]

I have an AR10-T that I'm trying to set up my FL sizing die for correct shoulder bump. Using a Sinclair shoulder bump gauge and my calipers fired FC cases measure 2.671". It would seem like I should bump the shoulder back about .003" with the die and aim for 2.668". However when I test chamber cases at this setting I can't get the bolt to close. I have to bump the shoulder all the way back to 2.664" to get the bolt to close. That works out to a .007" shoulder bump. Seems like too much re-size to me. Anyone else set their shoulders back .007" for a semi-auto? I've used Redding type S FL dies and a Forster Benchrest FL die and both require the same bump.

 

[427Cobra]

Re: Headspace for an AR10-T?

Punch the primers out first then use the tool to take readings, the primers flow a cunt hair backwards and sqew the readings

 

[esorensen]

Re: Headspace for an AR10-T?

I think my AR10T is labeled as 7.62x51 NATO. I'm pretty sure the chamber may be cut to those specs as opposed to that of a proper .308 WIN. I tried different variations of sizer die configuration, but I just ended up bottoming out the shell holder in the sizer die, as the accuracy remained the same regardless.

 

[V-Taper]

Re: Headspace for an AR10-T?

I set my shoulders back at least 5 thousands cause I had the same problem. I got a couple rounds stuck by dropping the bolt on them when I thought they were sized enough...now I just screw the die all the way down and bump the shoulder as much as possible.

Probably not the best way to do it but no stuck rounds, no failures to chamber, and no out of battery discharges.

 

[Jumper]

Re: Headspace for an AR10-T?

I re-measured fired cases but after I removed the primer. They were about .002" shorter without the primer. So this new measurement gives me about .005" shoulder bump. I can live with it but I think I should be able to get .003. Maybe my expectations are too high.

 

[427Cobra]

Re: Headspace for an AR10-T?

I think your GTG now, .003 bump is IMHO ideal for auto loaders, I also use a Lee FCD to put a slight crimp on 175smks so the bullets don't out any, more neck tension could be used instead though.