purchased cast bullet size

[winchester85]

i am not a caster, but i have shot many cast bullets. sometimes i would get leading, sometimes not. until recently i just figured i had to deal with it, or maybe decrease the speed.
after reading many posts on here, i see that bullet size is probably the most important factor in leading problems. however, it seems that potentially every bore is different.
i just measured some of the bullets i have, 45 colt and 38-40, the 45 colts measure .452 or just under, the 38-40's (2 different bullets and manufacturers) measure .400 to .401. if bullets should theoretically be sized a couple thousandths over bore size, why do mass producers size everything at nominal bore size?

if i dont know the actual bore size on my gun, where should i start? for a 44 mag SBH, should i go with .431, or .432? the last bullets i had were commercially made, and if i remember correctly they were sized at .430. i had significant leading in a stainless blackhawk.

[Wolfer]

The easiest way to slug your barrel is with egg sinkers. Their tapered at both ends with a hole in the middle. Find one closest to your bore size and drive it through your CLEAN and lightly oiled barrel. The hole down the center gives it some relief and let's it go much easer.

You also need to mic your cylinder throats. You can push a sinker through each one or you can push a 30-06 case into your cyl from the front and mark it then mic. May have to use a different cartridge case for the smaller calibers.

Your boolits need to be as big as the throats or a little over and hopefully that's bigger than your barrel.

If you go to Beartooth bullets web sight, find tech notes, Marshall has a very good article there titled Ruger America's best do it yourself kit.

[9-toes]

Everything is a guess until you slug the barrel and measure - use a micrometer . It's really not hard to do - should be in one of the stickies. After that you could probably use a Lee push through sizer to get what you need.