Home Forums Reloading Big Game Rifles Loading cast bullets for Micro Groove

I had good results from the 1895 Marlin Microgroove barreled gun with bullets running about 11 on the BHN scale. I sized them at .460". The Marlin has long since gone down the road but I still shoot bullets sized .460" in my Ruger #1S in 45-70.

I do think bullet size is more important in Microgroove barrels. Case in point. I was shooting cast bullets from my Marlin 30-30 as was another gentleman at the range. When the range went cold and we were changing targets he was moaning about how poorly cast bullets shot. I said I was shooting cast and had a nice 1.5" groups, not bad for the velocity I was shooting that day. (1900 FPS hunting load). As we talked I asked what he's sized his bullets too and he said .308 to fit the bore. I looked at his barrel which was nicely leaded and we then spent time getting the lead out. Once the barrel was decently clear of lead I had him shoot 5 of my load. A nice neat 2" group right off the bat. He asked what the difference was in my load from his and I told him to just try sizing the bullets to .310" which was I did.
I saw him a few weeks later at the range shooting his 30-30 and he was getting good groups. He said the changing in bullet sized made all the difference. I've always started working a cast bullet for a new cartridge at .002" over groove diameter and it's worked very well for me for many years.
Paul B.