That Lucky Gunner article is very helpful. Thanks for posting.
The author makes the point that he used two different 5.56 chambers during testing, and his first pressure graph does not stipulate that he used the same FN chamber for comparisons of 223 and 5.56 pressures. But from the context, it appears that he probably did.
If so, 5.56 is loaded to higher pressures than 223. That is what I had believed, but started to question in light of my recent suspicion that the Ramshot used CIP/NATO spec numbers and SAAMI test methods, which is a no-no.
The one big error I see in the Lucky Gunner article is that he did not appear to control barrel and ammo temperature. When I do strain gauge measurements, I stick a thermocouple to the barrel just ahead of the receiver. That gets rid of a substantial amount of measurement system error.
I have a note in to Ramshot. Maybe we can get some clarification from them on how they did their data.
Back in '02, when I did my article about converting CUP and PSI, the 223 Rem 55,000 PSI:52,000 CUP data pair was an outlier that did not conform with the rest of the data. Since it was the oddball of the data set, I took it out. In general, 55,000 PSI is equivalent to 48,300 CUP. I have no idea what kind of jiggery pokery produced the 52,000 number.
Anyway, although we're having great fun, we've drifted far from the original question.
Last edited by denton; 09/03/15.
