223 Failure to Chamber

[popeye4]

Hmmm, could it be your SCAR has a military chamber and your AR has a civilian chamber? This is an interesting little chart: http://www.ar15barrels.com/data/headspace.pdf

[GooseGun]

Just read your post about measuring headspace on the round. Never done that before so I'm unsure logistics on how to measure that. So I notice a few things today, I loaded 300 rounds with the RCBS T/C SB Die and I remember that I turned the die down 1/2 for crimp on a non-cannelure bullet instead of the recommended 1/4. Visual inspection shows that shoulder is slightly bulged. This is part of my problem. So with a non-cannelure bullet and a taper crimp die how much crimp should you apply if any?

[J-cat]

This is your entire problem. Too much crimp will buckle the shoulder and expand the case body which will stick the case. I don't crimp. But if you must, set the seater to apply only a slight crimp.

[GooseGun]

One other thing I noticed with a case gauge is that some will seat between the high and low mark but some will be over the high and it doesnt matter how many times I FL size it. It almost seams like the rim of the shell is whats keeping it from fully seating. The weird thing is these shells shoot fine out of my SCAR but they fail to close bolt in this guys DPMS. Is there a way to size or sand the bottom of a shell case?

[NoNOS67]

Hmmm, that's odd. Did you measure them after sizing, or after seating?