I recently bought a Clark Gator rifle, which is basically a DPMS AR15 with Wilson barrel. The barrel is marked "223 1-8". I assumed this meant a SAAMI-spec commercial 223 chamber. However, by long-seating a heavy bullet, I can tell the chamber has a long throat, although I have no way to measure precisely. Based on this, I think it is probably safe to shoot military-spec ammo without risk of dangerous pressure spikes, but I would like to be certain. I would appreciate any experience other folks have had with these barrels. Thanks.

strange as this sounds, standard DPMS rifles are chambered for 5.56 even though they are marked .223.

My DPMS AR has it stamped for use with
Caliber 5.56 -.223

Pretty sure new-arguy is right.  Ask DPMS in their forum or give them a call to be sure.

I have 1 rifle and 1 upper from them and I've shot M193 and Q3131A out of it no problem  (other than the fireball out of my 16" barrel).

Why don't you call Clark-Gator?

What the lower is stamped will rarely make a difference because it is the barrel (i.e. upper) that has the chamber. For instance, I built a Nice M4 with a 5.56 chamber on an old Colt lower marked 7.62x39.

Unless you have aq special edition DPMS that they may have made with the tighter .223 chamber, all their chambers are 5.56. Ask Jarod at DPMS... Im sure he will tell you the same.