Kelbro and I have been talking .44 Special loads on another forum, but since you guys are talking bores, throats, and leading, I thought I'd jump in here as well.
My .44 Special (standard run, non-Lipsey's) is a highly accurate revolver, but it leads up faster than any other gun I have. I usually shoot a 240 grain Missouri Bullet LSWC (BHN 18) or a 250 gr. Keith from Magnus (BHN 18-19). Bullets measure .430 in diameter. My standard load is 8.5 to 9 grains of Power Pistol, or 6.5 grains of HP38.
My theory was that 18 Brinell was too hard for .44 Special pressure levels (better suited to .44 mag), so to test this I loaded up 50 rounds using the Keith load of 17 grains of 2400. I cleaned the barrel of all leading until it was shiny and spotless. Then I fired 50 rounds and inspected the barrel. I had lead smeared from forcing cone to muzzle crown. Lots. Not like smooth bore lots, but enough that it's gonna take a while to clean. Accuracy was very good over the entire 50 rounds, though.
I have not slugged my bore, but the .430 bullets pass through the cylinder throats with very light, if any finger pressure.
I have a couple of things I want to try. First, a soft bullet. Like a swaged Hornady bullet, BHN of 8.
Second, try a .431 sized bullet.
I'm also willing to bet I have a bore constriction, but have not done anything to verify. Fire lapping would be my last resort.
You guys got any opinions/advice on what I've found so far?