4227 is used often in the .32-40.

32-40 likes 300 MP especially with magnum primers in some guns.4227 is ok depending on vintage and lot. AA#9 has worked well for me too. crapshoot, and it is what you can find.

Accurate 4100 and 300MP are what I use breech seating in several 32-40s

I am shooting the same rifle, by any chance is it a Darr barrel? If it is, check the twist. Most 32-40's are a 1:14 twist, Darr used 1:16 (at least in mine). The sweet spot for my rifle is with a Paur Jones 180gr bullet. The 190 is ok, but the lighter one shoots better in mine

So far, I have played with Ramshot Enforcer, H110, and am just about settled on 300mp. The enforcer was great, but the case would collapse after a few firings. The H110 gave great accuracy, and fixed the case collapse issues, but would throw the occasional unexplained flyer. I'll be using 300mp at my next match.

Randy
From one Randy to another, you might want to hold off on buying a mold for your new .32-40 so you can measure the precise groove diameter of your barrel. .32-40 Groove diameters between barrel makers generally run about .321 to .323. To deliver the optimum accuracy, your bullet diameter should be .001-.002 OVER groove diameter. There a lot more details to getting top notch accuracy but bullet diameter is one of the basic parameters.
Best of luck with your new acquisition, we hope to hear more from you as you get to shooting your rifle.

RSW wrote on Mar 11^th, 2025 at 12:00pm:

I appreciate the advice but I already ordered a 180, 0.325" mold. It was in stock and one never has too many bullet molds  It is a starting point and will, if nothing more, provide a point of reference. My goal is to find an accurate load in the 1100-1400 range. That will at least be my starting point.

There have been some examples of the use of 300MP in the .38-55 here now and then. Oftentimes the use of magnum primers is suggested. 

300 MP might have been brought onto the market around 2012. If we look in older CB sources, the 1986 RCBS Cast Bullet Manual lists one mold and (6) well known powders. The 1980 Lyman 3rd edition CB Handbook shows (2) bullet weights each with (5) again well known powders. Moving on to the 2010 Lyman 4th edition CB Handbook, there are
(6) bullet weights with 4198 showing up in (5) of the mold examples, but of course no 4227 or 300MP.

The interesting thing (to me) about the 4th edition is that Lyman lists some molds by others (example on page 78) besides Lyman molds. I asked the editor, Thomas Griffin, about that and he said it makes sense and is helpful to readers to see a few non Lyman molds listed. (I have a chapter in the book about the CBA match game, so I spoke with Thomas a few times.)

Is there more recent experience that anyone has using 300 MP in the .38-55? (I bought some 300 MP to try in my .41 Mag.) I do have 7-pounds of IMR 4227 and some 4198 that could be used in my newest project, a CPA in .38-55.

Thanks!

Tom