For what it is worth, the best I can tell both my .50 and .54 Scouts have 1:20 twist barrels both were made in the years prior to the big fire. The .50 loves a heavy saboted round I have yet to shoot the .54 enough to know what it likes but it chucked a 430g maxiball down a 50yd range first time out with 2" groups.

Before you give up on your .50 Scout try some stiff loads with heavy conicals you may be plesently surprized with the results but a warning you shoulder will not be amused.