I have some moly lubed and hard cast 158 gr RNFP bullets.

For powder I have A 2400 and trail boss.

How fast can I load these in my 6" and 8" 357's and not have leading issues?

Keep your velocities under 1000 fps and you will not have leading issues.

As previously state. Depending on the hardness, anything over 900 to 1000fps is going to lay down deposits. Lead bullets are cheap but there is a higher price to pay.

quote:

Originally posted by arcticat:
I have some moly lubed and hard cast 158 gr RNFP bullets.

For powder I have A 2400 and trail boss.

How fast can I load these in my 6" and 8" 357's and not have leading issues?

Trail boss loading data max is around 865fps. I didnt look at A2400. With a good lub and hard bullets, a cast bullet without a gas check will go to maximum vel. per the loading data. (1300fps) Leading to me is loss of accurcy. You will always have some fouling in the barrel, just like jacketed ammo.

The first thing I would do is get some pure lead fishing sinkers that are a bit larger than the bore and cylinder throats. Drive a couple down the bore and measure them. Assuming the slugs are .357" from the bore and .358" from the cylinder throats, your bullets should be sized to at least .358 to .359". If the cylinder throats are smaller than the barrel's groove diameter, accuracy will be poor and leading a problem. The cure is have a competent gunsmith open the cylinder throats to at least .358"
I don't use Trail Boss, but the original loading for the .357 Mag. was 15.5 gr. of HERCULES #2400. Now that ALLIANT is making #2400, the max load with a 158 gr. bullet is 14.0 gr. Whether the change is because the ALLIANT powder is somewhat faster burning or the change in load data is in deference for the hotter loads shaking the "K" frame S&W loose is something I don't know. Could even be a combination of the two reasons.
Paul B.
If your guns are Smith & Wessons, unless they've made a change, you'll have five grooves and lands which makes getting an accurate measurement a bitch.