I bought a Steven's 44 1/2 rifle in .38-55. I've looked in my reloading manuals (some back to the 1970's when I first started reloading and some brand new). I can't seem to find a load for a 255 Gr. lead Postel bullet. I contacted Hodgdon and while I got some loads the bullet weight (from Lyman cast bullet manual) listed 24 gr of IMR 4198 for a 249Gr (375248) and 20 gr of IMR 4198 for a Lyman 375449 264 Gr bullet. From Load Data (a subscription service) I get 20 gr of IMR 4198 behind a 255 JSP. 
I leaning toward 20 or 21 Gr IMR 4198 to start. 
Does anyone else have a better suggestion (I know trusting internet data could lead to TROUBLE, but I think I have at least a starting point, just looking for tweaks/suggestions).
The cast bullet BTW is a Steve Brooks Postel 255Gr.
Thank you to all who have more experience with this rifle/load/reloading than I have. Previously I've only shot black powder in my .38-55 Ballard with 255 Gr bullet.
Again I appreciate your help.
I listed the powders I have available, hence all the IMR powders. I do have Unique too if that would be a better option. Or point me toward a manual that actually has the bullet type (cast lead) weight (255Gr) and in this caliber (38-55) and I'd be happy (assuming I can locate the manual

My 38/55 smokeless  loading data comes from two sources loads other guys have recommended  over the years and data from Sharpes 1937 complete guide to Handloading. This cross referenced with other vintage manuals too.  4227 is essentially a replacement for  SR # 75 and Unique is the Unique we use today. SR # 80 also in Sharps book is essentially 4759 no longer produced .  

4227 38/55 load I use for a 255 gr cast bullet loaded fixed is 17 grains. It’s straight from Sharpes book after switching powder numbers to reflect the newer product. It gives Black Powder velocity’s allowing switching propellants according to match rules with similar sight settings. Have used light charges of Unique also from Sharpes book when sub sonic is required gallery 

The 17 gr 4227 load is very mild and gives complete combustion. Have used the other powders you mentioned don’t think any are optimal for 38/55 255 gr. Others may 2nd my advise or disagree. 

Boats

Noted 45/70 mikes comments. He is correct 4198 can be very good with heavy bullets in the 38/55 . Many if not most new made 38/55 rifles will have fast twist barrels and handle 330 gr bullets well. Original guns and early CPA rifle’s like mine are 18 twist and pretty much limited to 300 gr bullets. Lighter bullets with a slower powder  like 4198 not likely to give complete combustion or need fillers to burn properly.

That’s why I stick with 4227 in my rifle, 255 gr bullets . If you want to test run a dozen or so shells through the gun. Then push a single lightly oiled patch through the bore. On the ground set the patch on fire. Unburned powder will “ fizz” very different  than powder soot, it won’t ignite.

Boats

Unburned powder will “ fizz” very different  than powder soot, it won’t ignite

I do shoot a 250 gr. slug with the same 18gr. of 4198.  Usually an OH load.

I'll have to try your "test" and see if it "fizzes" 

Thanks,

Mike.

4198 (corrected) is good it’s just different and best suited for a heavier bullet.  Think about your rifle like a internal combustion engine. Diesels are heavier operate slower at higher pressure and use slower burning fuel. Gasoline engine lighter higher rpm and uses faster burn fuel. 

Guns no different heavy bullet cartridges typically use slower powders light bullet ctgs faster powders. Get a relative quickness powder chart off the internet & have a look at the various powders burning speed.

My CPA 38/55 was built 1993, at the time most production 375 barrels were 18 twist. Faster came later as people appreciated performance possible from a longer 375 bullet.  That’s the reason new made 38/55’s are 375 instead of original size .380. 375 was available. Might check your original 44 1/2 barrel for bore size as well as  twist. Never owned a original can’t say what they are.

Again that’s more what I think than what I know. Might be wrong 

Boats

4198 is one of my favorite rifle powders and I use it in numerous large cases. That data for .38-55 with higher charges is pretty toasty, and I'd stick with 18-20 grs. of 4198 to start out, and you may end up staying with that range forever.

Ranch13 wrote on Jul 30^th, 2024 at 11:08am:

Don, I hear a lot of shooters out your way are moving to Blackhorn and having great success at the Quigley, Baker, Ekalaka shoots etc, Not cheap at $80 a half pound.

BH209 was pretty popular for a while, but then when the KIK factory closed, it pretty much disappeared. It's back now but terrible expensive.
I still have a few cans it works good in the 45-70, never tried it in the 38-55, was thinking about giving it a run in my wcf chambered guns, just to safe on my meager supply of OE 3f.

Some have reported good results with the buffalo gun? powder but I haven't ever tried it.