As for the ID-OD issue, I am not sure which is "correct", and suspect that neither is, since what is involved is relative pressures, not necessarily absolute.
It used to be a designer took the highest number, even though it is only reached for a millisecond, and that became the design load. With the advent of computer models, deflections can be modeled in real time, and that might affect the analysis.
The folks who write that cartridge X and bullet Y give 52,286.745 pounds per square inch are not in the real world. I once wrote that there can easily be 100 fps +/- variation in a box of factory cartridges and was taken to task by some guy who read the tables in the Gun Digest and believed the numbers.
Agree about pressures not being a point value: when I found actual pressure data, the spread is much more than we have ever been lead to believe in the popular gun press. An excellent read on this can be found at
http://kwk.us/pressures.html.
Based on this, and basic statistics, given a standard deviation, the frequency of a high pressure shot is surprizingly high.
Page 1-9 AMCP 706-110 on page 1-9 gives pressure data, which is either taken from the 30-06 or the 308 Win. The book gives the example of a 50,000 psia cartridge with a std deviation 5,000 psia. I have seen pressure tested data on the 308 National Match ammunition, with the 168 match bullets, and the limited tests showed 1719 psia standard deviations, so I consider a 5,000 psia standard deviation reasonable over a large lot.
Based on this standard deviation:
15.9 % cartridge have pressures above 55,000 psia
2.3% have pressures above 60, 000 psia (about 2 in every one hundred rounds!)
1.2 % will have pressures above 65,000 psia. (about 1 in every one hundred rounds!)
So I believe the short hand calculation that SAAMI uses for Maximum Extreme Variation (MEV) to be quite reasonable. From
http://kwk.us/pressures.html
Maximum Extreme Variation (MEV). There is a small chance that in a very large lot of ammunition, a single sample might test much higher than the averages. From statistics, SAAMI recommends an MEV no more than 20.6% above the MAP.
338 Win Mag 1.206 X 65, 000 = 78, 390 lbs/ in ²
It can be seen that at least once or twice in every 100 rounds, you can expect an 78,000 psia shot with 338 Win Mag factory ammunition!.
Just imagine the extreme high spreads on some people's reloads! Might be some 90,000 psia rounds going down the tube on the rare occasion.
When people raise the bolt loading flag, which they often do, I believe my best advice for that concern is to "cut your loads". Nothing increases bolt loading faster than a couple of extra grains of powder. Believing that case friction is a panacea for high pressures (Ackley anyone?) is about as realistic as believing you can survive a 100 mph car accident, because you put a pillow between your chest and the steering wheel.
I once did a firing time line in milliseconds and there is not a lot of that "slow push" we read about going on. Bolt lugs get slammed back fast, no matter what the design is.
Agree, I think Chinn calls it an impact load. Based on discussions with a number of people, treating the load as an impact load has greatly changed my view of heat treatments, and the great importance of looking at Charpy impact test data.
FWIW, I have long considered the AR-18/180 to be a much better rifle than the AR-15, and I think had it been ready in time it would have been selected as the M16 rather than the earlier rifle. It would have been more reliable, less fussy, and much cheaper to manufacture. (I would have made the buttstock connection a lot stronger, though.) But the political demand was to get something out there to counter the AK-47 and the AR-15 was all there was.
Once something is type classified, goes in to mass production, is issued, it gets very hard to replace. The logistics cost simply overwhelm all other considerations and the political will was not there to force the issue, as there was on replacing the M14 with the M16. Maybe once burnt, twice shy? I have handled an original AR180, looked like a better mouse trap to me, but, “good is the enemy of better”. Currently the military is requiring any replacement candidate to the M4 to be 200% better. I don’t know if there is anything using current materials, technology that will ever be 200% better. These sort of standards cannot be met unless Captain Kirk beams down a couple of phaser rifles for evaluation.
I considered the vaunted Stoner 63, though, as "simplifying" things in a very complicated way. It was a "tour de force" that wasn't needed, though it impressed the heck out of some generals with that "push-pull-click" stuff. But an army just issues rifles to some and machineguns to others - they don't need to be convertible or combinations.
The early M16 had a slamfire problem: primer sensitivity was not specified and exactly what accidents happened, not in any record, but the military reduced firing pin weight and went to a less sensitive primer: the #41. The M16 firing mechanism was not altered as there was enough energy margin to fire the less sensitive primer even down to -40 F. (or -40 C) But, Stoner's 63 version had misfires with the #41 primer!, he must have changed something.