After seeing the burn rate that works best in this cartridge I wanted to note that Wideners has some Swiss powder with 4198s burn rate on sale. I got some, think it'll work well in the 35Rem too. My 35 really likes Accurate's 2015. Single Digit SDs, which indicates full burning of the charge, to me. I'd think Varget would be on the slow side for your cartridge. Usable, but slow.
The (3) powders that I've used in my Savage 1899 38-55 with Lyman 375449 280gr GC are Reloader 7 (26gr), AA2015 (28-30gr) and AA2200 (30-32gr). These are not hot loads, but not intended for weak blackpowder actions.
Another powder that I may try is H322. IMR 4198 should be good as well. As already mentioned, 4227, AA5744, 2400 etc should all work.
If you notice, these are all relatively fast burning rifle powders. It depends upon how fast you want to go. With a 250gr or less plainbase bullet, Unique can work just fine provided you don't get carried away. Lyman lists 9.5gr under the 250gr 375248 at 1170fps. Its not a load that I would want to hunt deer with.
I used Unique in a Marlin 1893 marked "For Blackpowder". It wasn't a function of action strength, but soft barrel steel in that case. The bullet was the Lyman 375248, and I had no issues with melting bases, but didn't exceed 9.5gr or so.
Fit is everything. If you have a good fit in the bore and throat, you'll not have gas blowby which is a cause of leading. After that, you'll need a lube that works for the entire length of your barrel. With a good fit and lube, you should be able to shoot relatively soft bullets without issues.
PM me your address and I'll send you some bullets.
Just a thought. There is no need to hot rod an old Winchester or Marlin 1893 even though they say for smokeless. The steels of that period are not the steels of today or even the 1960's. Further, the benchmark cartridge, the 30-30, was loaded to much less pressure today. What I'm getting at is that a steady diet of modern 30-30 with jacketed bullets will wear the bore. Even worse is that the rifle will develop headspace problems and the same goes for Class III loads for 38-55.
As the basic reference for loading the 38-55, its hard to beat Ken Waters 'Pet Loads'.
And ditto on getting the correct Starline brass for your vintage rifle or for the Marlin 336 cowboy.
BP | Bronze Point | IMR | Improved Military Rifle | PTD | Pointed |
BR | Bench Rest | M | Magnum | RN | Round Nose |
BT | Boat Tail | PL | Power-Lokt | SP | Soft Point |
C | Compressed Charge | PR | Primer | SPCL | Soft Point "Core-Lokt" |
HP | Hollow Point | PSPCL | Pointed Soft Point "Core Lokt" | C.O.L. | Cartridge Overall Length |
PSP | Pointed Soft Point | Spz | Spitzer Point | SBT | Spitzer Boat Tail |
LRN | Lead Round Nose | LWC | Lead Wad Cutter | LSWC | Lead Semi Wad Cutter |
GC | Gas Check |