Re: Hornady steel match ammo.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TAZ</div><div class="ubbcode-body">I have run around 300 rds of the 75gr training ammo through my SPR clone built with a WOA 1:7 barrel. Pretty sure its a 223 chamber instead of 556 and I can't see any markings on the barrel right now to verify. Have had no issues, actually it been some of the better shooting stuff aside from Fed GMM 77gr. No failures, no grit, carbon nothing, although I am pretty anal about cleaning after range session. For me the accuracy limitation was not the ammo, but operator head gap. 1 MOA @ 100yds was doable without trying hard. </div></div>
If you can shoot USGI M193 or NATO M855 type ammo without getting pressure signs, your chamber (really the throat or leade) is 5.56, not SAAMI .223.
Though I remain somewhat skeptical that this widely-cited but somehow infrequent problem is solely the fault of the ammo, there remains the inescapable fact that the mild steel of this type of ammo is harder and less elastic and slightly less "springy" than brass cases.
I'm pretty sure that high-speed photography would show a larger gas puff from the chamber with steel case ammo than with brass cased. They both do it, but the question is how much and how many rounds is enough to grab a brass case...which expands more and tightly seals the chamber more to the rear than steel, at least in my experience.
And the 5.56/.223 in my strong opinion is under-designed on the extractor rim anyway. If I could wave a magic wand, I'd have made a mid-stream design change like what happened to .300 Whisper/Blackout, with the rim getting twice as thick back when the M855 was adopted. An extractor changeout on existing M16A1s would have been all that would be needed, to allow "emergency" use of keyholing ammo...and I've seen some pretty sloppy extractors fitting that loose that worked just fine (as far as old stocks of M193 would go).