Greetings WillB,
My son had good results with AR2208, 3,650 fps and Benchmark 8208 in his 26 inch barrel XR 100. You should expect to loose roughly 200 fps in your short barrel so Benchmark 8208, aka IMR 8208 XBR, could be a good bet. Data is on the Hodgdon and probably ADI sites. H380 is a ball powder, originally surplus, so there is no ADI equivalent.
Regards Grandpamac
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