From time to time there have been questions about suitable loads for the .45 AR. In going through some stacks I came across an article, "Handloading the .45 Auto Rim" by Brian Pearce in
Handloader magazine, August/September, 2008 (Issue No.254). He tried a lot of loads in 1917s, a 25, and a couple 625s. Some of his main points were:
1. Factory .45 AR was loaded to lower pressures than
.45 ACP. The AR cases and any revolvers chambered
for .45 ACP should be safe to 23,000 psi, however.
2. Chamber mouths vary considerably in diameter. Guns
with .451 or .452" mouths work best. (As we would
expect.)
3. Swaged lead bullets skid and lead the bore. Jacketed
and hard cast lead pills (16+ BHN) shoot more
accurately.
4. Brian favors heavier bullets (250-280 grs) because
he likes to hunt and thinks they are more accurate.
He lists a lot of loads, many of them fairly conservative, using fast to medium powder. One of his hotter ones, 8.0 grains of Power Pistol, pushed Hornady 230-gr XTPs to 985 fps (4" barrel). Another warm one, 11.0 grains of 2400, pushed RCBS cast 280 grainers at 851 fps (6.5" bbl). In general, loads equivalent to factory .45 Colt rounds were easily obtained with a number of powders. Not many details concerning group sizes were given.