The 45-70 and Trail Boss

I load either 350 grain Berry's plated bullets or 405 grain cast lead.

My Hodgdon 2021 "magazine" shows loads only for cast lead bullets and (naturally) only for trapdoor rifles.

300 grain LFP  14.0 to 16.5 grains  1199 to 1285 fps
385 grain LFP  14.0 to 16.0 grains  1075 to 1142 fps
405 grain LFP  12.0 to 13.0 grains  971 to 1007 fps
485 grain LFP   8.0 to 10.0 grains  699 to 804 fps

My own notes show that I loaded 12.3 grains of Trail Boss with a 405 grain lead bullet in March of 2009 and was entirely satisfied.

They say to not use Trail Boss with jacketed bullets. The reason is that Trail Boss does not have enough push to consistently get the bullet out the end, so there is a risk of a stuck bullet.

What about with Berry's plated bullets? Berry's says that you can run those bullets up to 2000 fps, which is not anything I intend to do.

At some point IMR published this statement:

Trail Boss was designed primarily for reduced loads using lead bullets in pistol cartridges. However, Trail Boss offers superb versatility in rifle cartridges producing reduced loads using lead or jacketed bullets. These reduced loads make firing such cartridges as the 300 Winchester Magnum or even the 458 Winchester Magnum pure fun!

Note that the above statement back-pedals from the general prohibition against using Trail Boss with jacketed bullets -- but only from a rifle!

A .357 Magnum load for a 158 grain lead bullet with trail boss is 3.2 to 4.2 grains (Hodgdon 2024 manual). The load for the same bullet in a .38 is 2.7 to 4.2 grains.

IMR told one fellow to use the higher end of lead data for Trail Boss for the same weight plated bullet.

Here is a good discussion:

• Trail Boss and plated bullets

I use the Berry's 350gr plated bullets over 14 grains of Trail Boss powder for my Marlin 45-70. It makes a very easy shooting subsonic plinking load. If you have a can, they are fantastic! You can shoot these all day without problems with your shoulder! Highly recommended.