I shot one of the best cast bullet loads I have fired today, did it 3 times to be sure, got it all three times.
I made up some 20:1 alloy this week and cast some Lee 340 grainers for my 45-70, and some 265's from a modified Lee 310 for my 44. Shot them today. The 44 bullet shot 3 ten shot groups that can be covered with a 50 cent peice. The load was 11.3 grains of milsurp #107 (jeff bartlett @gibrass) touched off with a Federal Large Pistol Magnum primer. To give an idea, this load usually produces 2.5" groups or better as I have tried it many times and haven't considered the load good enough to even keep targets from. I kept these.
As I was casting with this new alloy, I found it to be casting undersize. Through a thread on another forum, DJ pointed out that spray mold release on his molds cast undersize bullets. I removed the coating from my molds and sure enough gained .002-.0025 in diameter.
I finally broke down and slugged the bore of my 44 as my bullets cast .432 and I figured I was large enough to get a good fit. I took a bullet that was a tad over .432 and found my groove diameter is .432 and the bore is .427 as measured using small bore gauges. I had been shooting bullets that were only .430 at best, as I was running them trough a lube sizer to lube them, the batch today I pan lubed.
Went on to my 45-70. used a load of 17 grains of this same powder which usually shoots about 2" and the group went to 4" using the 20:1 bullet. Go figure. I've put a new scope on the 45-70 (actually it is the Simmons I got for the 30-30) and the IMR 3031 load of 47.5 grains under the 340 continues to shoot less than 2", this with a bullet that starts out .002 undersize, is plain based, and driven to 1600 fps, and at least 15 BHN if not more. Ergo, Eureka Weirdness.
Euraka, I've found a cast bullet load for my 44 that SHOOTS. Don't know how much faster I can drive it, but this is as consistant as any cast group I've seen in 2 years with this rifle and better than I have ever fired with this bullet/powder combo.
Weirdness, a load that shouldn't shoot well at all from my 45-70 continues to be the cast bullet load that produces the best accuracy and high velocity without falling apart. (high velocity being anything over 1300 fps with a cast bullet)
As a side note, I took a 30 cal cast bullet (Lee's .312 180 grainer) and drove it into the muzzle, the groove diameter is .3105, the bore measured with small bore gauges is .307 I've had no trouble getting exellent groups from this barrel with .308 jacketed bullets and no end of trouble getting a cast bullet to consistantly shoot decently above 1200 fps. I've no doubt that to get good cast bullet performance from this barrel I will have to get a custom mold made for it, or simply relegate it to jacketed and even then I'm highly inclined to try .311 bullets to see how they shoot.
I've got to get a lead .490 ball to check the groove diameter of my 45-70 Small bore gauges say my bore is .452, but I don't have an oversize bullet to check the groove diameter, my mold is dropping .457 and if the groove diameter were larger, it wouldn't show.
I'm sure a lot of folks shoot cast and never check their barrels for size, yesterday I was in that group. After today, every barrel I have I expect to shoot cast in will be checked for size.
