I have run about 300 rounds through it so far messing around with cast bullets. I first had some .310 LaserCast 165 grain, non gas-checked, that would not hit a 10" square target at 50 meters consistantly. I tried several combinations of powder and got more or less the same results. I have always had excellent results with the LaserCast bullets and this was a big disappointment.
Got hold of some .309 170 grain gas checks that shoot very well indeed in some other rifles owned by acquaintances. They are a little better but I experienced severe leading over about 1500 FPS, same as the LaserCast. Only could shoot about 15 shots and then might as well throw stones. They do pretty decent around 1300 fps but after 40 rounds there is still some leading.
Finally slugged the bore. Guess what, .310 diameter bore!!
So now I figure the bullets are stripping, which is causing the poor accuracy and leading. I have some 115 grain cast bullets .312 diameter for 32-20, I intend to try a few of those. Makes me wonder what the rifle would do with .308 diameter jacketed bullets, probably strip those as well??
My friend back in Wyoming has an identical rifle and we messed with it all summer and couldnt get it to shoot cast, probably for the same reason. The guy who casts the gas checked bullets told me he had a Marlin model 30 (?) the predessesor to the 336a, he slugged that barrel and got .311. Go figure.
Guess I have learned my lesson to always slug a bore before messing with cast.
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