I have used HS-6 for building some full steam 9 mm loads. It might be a bit on the slow side for a short barrel. AA#5 might be worth a look.
+2 on RC's post. reason being as I recall looking at graphical depictions of pressures recorded in testing shows pressures to peak very quickly even with slow powders for a given caliber. It looks like most of the bullets acceleration happens in the first few inches of barrel even with rifle calibers. If memory serves me correctly the slower powders have a broader peak. Of course my memory's questionable these days. I bet google would find some pressure graphs for you. I may do that myself to refresh my questionable memory.