Good question. The only supersonic rounds fired to date were some round balls just a few days back. I am reasonably certain that supersonic is doable but can only speculate on that point. Depending on powder choice load density ranges from about 50% to 90% when tickling the 1050 FPS realm.
Case capacity to the neck/shoulder junction is weighed at 13.4 gr. of H2O. Case capacity with a sample of powders vs loads and velocity follows:
Reloader 7 10.4 gr - 1059 FPS / Capacity 12.7 gr
Li’l Gun 6.5 gr - 1032 FPS / Cap. 13.5 gr.
SR 4759 7.8 gr - 1063 FPS / Cap. 9.1 gr.
I have limited additional info but I think this illustrates the landscape. The case holds about 17 gr of Swiss 1.5...,😁
The Brooks bullet weighs ~180 gr with 9 BHN alloy. JBM calculation puts the G1 BC at .413 with a velocity of 1050 FPS.
I have not toyed with SS velocity calculations at all, nor do I have any reliable pressure data. An acquaintance did a little work up with one of the load calculators with preliminary data on case dims, none of which correlated to actual chrony data at all. I’m using Starline brass and some has been fired over 20 timed w/o case loss. I anneal about every second firing.
My gut says that something in the range of 1500-1700 FPS is possible, but that’s just a WAG. What that looks like at 200? Haven’t a clue. Very early testing with loads/alloy long abandoned on the 100 yd line yielded 5x groups of about 3”.
