Re: Hornady Superformance in M1A?
ALL this is almost meaningless until and unless someone gives you reliable information on the port pressure generated by that load.
You have Hornady and SAI saying it's okay, which would *tend* to *imply* that the port pressure of that ammo would be somewhere, and reliably, less than the 14,500 PSI (CUP) which lies at the upper end of the USGI port pressure standard of 12,500 CUP +/- 2,000 CUP. The port is about 14.1 inches down the barrel from the boltface, which by my reckoning is about 12.5 inches of bullet travel for you QuickLOAD people.
Four things I can tell you:
1. An M14 type op rod is nothing like an M1 Garand op rod, when it comes to getting hammered or "bent."
2. I have fired loads that mathematically model out to about 15,500 CUP or so port pressure and my op rod still clears the receiver at the one place and the two directions where it counts for NM reliability mods. The result was 10-20% failures to extract and some pretty severe rim lift, and one torn off extractor rim. These were with 155-gr bullets and Varget.
3. Several popular loads in .308 using 175-gr bullets and RL-15 do model out as giving excessive pressures at the port up to 100 fps before the chamber pressure exceeds specs.
4. NRA testing in the CUP days showed that with the powders of the day (IMRs and H- and maybe including WW-748), the heavier the bullet, the LESS the port pressure. The author was either Davis or Clark, and I think it was about 1982 or so. A clever man could find it. AFAIK, it is the only general-circulation article ever published which listed both the USGI port pressure standards AND actual tested pressures at the port.
Though I'm skeptical that SuperFormance could lengthen the very short peak chamber pressure curve for the first 6-10 inches of bullet travel without having pressure higher than RL-15 at 12.5 inches of bullet travel, I would be dishonest to comment further without seeing the time-pressure curves for the ammo.
So, now you know what to ask Hornady and SAI. If they are willing to put numbers to their "it's okay" assurances, in writing, I'd believe it.
The rest of the pressure problems being reported are, I believe, either soft brass, rifles which probably produce beyond-spec pressures with other loads, or a combination of both.
