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The starting load is listed at 6.5 - 927 fps, with max listed at 10.2 - 1374, so your load would seem to be super, yes. Dial it back a bit, you'll be safe at subsonic speeds

Most any pistol powders would do the job surely? Titegroup, N320, etc etc You still out the bottom left hand side of the tron?

A starting load of AP70 with a cast 240 SWC is listed at 927fps from...