I cast and shoot lead bullets in all of my handguns, and for my 1895 45/70. Those work pretty good.
A couple of months ago, I pulled out the old microgroove 30-30 and decided to work on the thing until I was able to get acceptable accuracy from cast bullets. I shot several groups before I did anything to the rifle, and at 50 yards with 311041, was only able to get 2.5 inch groups. The load was 26 grains of 3031.
I slugged the barrel, and found that it had a 0.02" constriction about midway down the barrel. After a great deal of work firelapping the barrel to remove the constriction (which, for reasons that I won't go into here, I'll never do again) I set out to the range to shoot my newly reconditioned barrel.
The post-firelapping groups that I shot were loaded with the same bullet (311041), cast with WW, 2.5% tin added, and waterdropped. The bullets were sized to 0.310" (the bore slugs around .309", but I've had trouble getting a consistant reading on this.) The first 20 rounds were loaded with 10 gr Unique, and these bullets grouped around 1" at 50 yards, which is about all that I expected. No leading.
Then, I started shooting groups loaded with 3031, beginning with 22 grains. The following sets included 22.5, 23, and 23.5 grains 3031. The 22 grain load should have had a similar velocity to the 10 grains of Unique. I cleaned the bore after each 5 round group.
ALL of the 3031 loads leaded the bore severely. Not only was there lead in the bore, but it came out in long thin pieces matching the geometry of the grooves. Each time I cleaned the bore, the first patch had 12 pieces of lead on it, each about an inch long matching the groove. It seems that the lead bullet was shearing off into the grooves.
These bullets loaded with 3031 were not loaded very hot. I can't understand why this bullet won't shoot any faster than 1500 fps without leading severely. Am I expecting too much from a cast bullet in a microgroove 30-30?