Have been trying to get my Bullard single shot to shoot accurately with a 160g x.326  boolit.  So far not so good. Bullet seems to stabilize, but accuracy leaves a lot to be desired.   The bore is excellent, it measures .3255 in the grooves and has a 1 in 15.5 twist.  Maybe cut this way for paper patching?? I don't know.  Anybody use the Greenhill formula for twist rate and does it work?  My calculations say I need a bullet .990 to 1.03 in length, but this gets the weight way up there.  With the slow twist, a heavier boolit may not stabilize.  Any suggestions?

I know there are a lot of variables here, not just bullet weight, but I have been using 11g of 4227 seated in the case.  20:1 alloy.  Tried going up a little to 12g and down to 10.5g, both groups got worse.  My main concern here is the proper bullet weight for that slow twist.

I think you need more powder. Assuming you are shooting a sufficiently strong rifle I would use 14 to 14.4 grains of IMR4227 with a bullet of about 190 grain-maybe as much as 200 grains, breech seated 1/16" ahead of the case. It should shoot ok. They have shot them like that for 60 years or more and they have proven to be accurate enough to shoot 248's or so. Probably would even shoot a 250 with the right guy behind the rifle. Just my opinion and observations. Your results may vary since I don't know all of the facts. If you want to continue with the 160 grain bullet maybe 13.5 grains of 4227 would be enough, but another grain probably would not hurt. I don't know if I believe that old story about paper patched barrels not shooting grooved bullets well. I have a Hepburn that was definitely made for patched bullets and it is a great shooter with grooved bullets. I suspect the problem people had was in not shooting bullets of a large enough diameter.