Thread: Neck sizing for AR-15 platform

is anybody doing this? seems to be quite a bit of conjecutre over weather you should full length size only for semi-autos, and it gets even more mixed up when the lee collet dies get talked about as well.

Any inofrmation appreciated.

No, you should always full size for semis. Although if you want to body size the bump the shoulder and then neck size, you will be okay. But you may as well just full size the brass then.

Thanks dogmatix, is that due to the increased liklihood of chambering issues with a semi?

Pretty much. The AR15 need the bolt to fully lock and rotate, its easy for it to not fire if the case is deformed or bulged, it wont fire. and it doesn't have to be out by much for it to fail to fire.

Small base resizing is always a good option as well.

Neck sizing = stuck cases. If you want to size the neck without over working it, better concentricity etc, you can use a FL bushing die, you will just have to go for tighter neck tension than you would with a bolt gun. I think 4 thou is the recommendation. You need to bump the shoulder of
the case between 2 and 4 thou and size the body well for reliable function in a semi.

FWIW I full lenght size all mine using small base dies then the finished ammo all goes thru a JP case guage. No jams ever since