John states:

"The main point from the other thread was that the 45 GAP is loaded to higher pressures than the 45 ACP to achieve the same external ballistics."

The problem I'm having with your comparison of Hodgdon data at the other site is that the ACP rounds were measured in CUP and the GAP rounds were measured in PSI. According to SAAMI standards, here are a few rifle "equivalence" examples to show variance in the two methods of measurement:

222 rem cup: 46,000 psi: 50,000

284 win cup: 54,000 psi: 56,000

30-30 win cup: 38,000 psi: 42,000

And here's a Hodgdon example you pointed to:

200 gr acp with Clays: 17,700 CUP

200 gr gap with Clays: 20,400 PSI

In the earlier days, cup and psi apparently were used interchangebly even though psi was incorrrect since the copper crusher method was used.

Now, there really are labs that can measure psi accurately with a piezoelectric and strain gauge. For example, for years the max pressure for the 270 Win was listed as 52,000 psi (really cup measurement). Then more recently, publications have been showing 65,000 PSI (true psi measurement) for the 270 Win.

So I'm just wondering if the pressure difference you mentioned in referencing Hodgdon data comparing cup-acp and psi-gap is really comparing apples to apples? I further wonder if the pressure difference in the two calibers is significant with factory ammo since so many shooters can't seem to tell the difference when shooting the two calibers.

Another interesting fact about the Hodgdon comparison is that the gap basically matched the acp velocities even though the gap loadings used significantly less powder grains for HS-6, Universal, HP-38, Titegroup, and Clays. That would be quite a savings for reloaders.

just curious, not fanatical. :?