I have been having a bit of leading with my .38-55 and a Lyman 250 gr flatnosed bullet using bp loads and SPG lube. I originally thought it might be up in the muzzle where it leads, but now, I'm not so sure. The amount of lead is very small, and it comes in flakes, not strips.
I thought I might check bullet size vs. groove diameters, and in doing this, I found something interesting. First, the bullets are sized, and miked to 0.377". The breech measures 0.3763" and the bore measures 0.3768" - at least to the best of my abilities to measure.
To do this measuring, I tapped a sized bullet into the bore for the first three bands and then tapped it back out. I did the same for the breech. For the bullet that went up the breech, I found that the rifling marks looked normal with some finning on the backside of each band as to be expected.
But the bullet that went into the bore, when examined under a 5X loup, showed not just finning but fragments of lead cracked off of the back sides of the bands. The lead that had been pushed back by the smaller diameter of the bore and grooves was rolling and cracking off the back edges of the bands, and not just where the rifling passes but also in the grooves. This lead would probably be falling off the bullet as it goes down the bore and may well be the source of my leading problem.
Both bullets were 25:1 Pb:Sn so I don't think I have excessively hard or brittle bullets.
My questions to the board are,
1. Have any of you seen this?
2. What to do about it?
I certainly have never seen it but the only solution I can think of to fix it is to switch to paper patched bullets.
Brent