I have a new rifle sporting a Green Mountain .50 cal. barrel. Range testing so far has indicated a .490 RB with some .018 JC Pennys pillow ticking gives a nice fit and the patches are almost reusable. 70 & 80 grain charges of Swiss 3F black powder have not produced a satisfactory group. Any suggestions from those among the readers of this forum that have GM .50 cal. shoot'en irons would sure be appreciated. Thanks.
Same patch with .495 ball.
Should load easy.
75-90 gr of FFF Swiss.
Patch lube can be very important so try some different lubes. Different level of lubricity can change how the barrel shoots. A slick lube may need more powder than a drier lube.
Wiping every shot is also important for best accuracy.
I would recommend you get Dutch Schoultz's booklet.
It is a great place to start.
Barrel should shoot into a ragged hole at 60 yards once the load is found.
1.5 or 2F Swiss may also work well.
Dan