I have a Friend that bought a Hi-Wall in 38-55 30" bbl about 18yrs ago. I don't remember the Manufacturer. It might have been Pedersoli.
I was stuck with the job of making it shoot Cowboy Long-Range.
I started by dropping one of my own loads into the chamber. It didn't fit. I load a Lyman #377449GC, cast of #2 sized .380dia for a .379bore and a non-existent throat. There is just enough throat to allow crimping in the bullets crimping groove. As long as the case is trimmed to 2.075. Winchester cases only, starline cases are too thick.
My .38-55 Rifle is a Winchester Commemorative: Chief Crazy Horse, made in 1982.
The Hi-Wall's throat is shorter, I have to crimp over the bullets first driving band to allow the round to fully seat in the chamber. Fortunately his bore is .3785dia, I used 50/50 lube and seated gas check with a Lyman gas check seater and then sized and lubed.
The load uses IMR3031, a middle weight charge according to what the Lyman Cast Bullet Handbook #4. In my Lever Gun if I raise or lower the Powder Charge by 2.0grs and accuracy goes to blazes. No key holing but groups open from 2 1/4" at 100yrds to 4"+ from the bench. I put a no name tang peep sight on it in 1990, uses the factory front. Lyman wasn't making Tang Sight yet.
Back to the Hi-Wall. Groups weren't bad at 3"+ from the bench. A Tang Sight was added and Bear Creek Bullets of .379 were purchased. My friend preferred the Moly-Coated bullets.
Accuracy was decent enough at 3+" at 100yrds for my friend.
He traded off the 99 starline cases and I gave him 60 WW cases. He doesn't shoot Cowboy anymore so I guess the Rifle just sits in his safe. I would have liked to continue to work with it. Try some IMR4198 or SR4759, fool around with another bullet. Even bought a Lyman #380681 to try a softer alloy. I choose the #2 originally because it cast big enough.
I always wonder if I remembered enough to do everything I was supposed to. The only Lever Guns I loaded for were .30-30 in a Win 94, .45-70 in a Marlin 1895 with microgroove Rifling and later a Marlin 1895CB. And that 94 in.38-55.
It was 30yrs too long ago that I loaded any other Levergun Calibers. Forgot most of My Dad "Tricks". And he wasn't around to ask.
Just what I did, hope you might find something usefull in my ramblings.
Long time Caster/Reloader, Getting back into it after almost 10yrs. Life Member NRA 40+yrs, Life S.A.S.S. #375. Does this mean a description of me as a fumble-fingered knuckle-draggin' baboon. I also drool in my sleep. I firmly believe that true happiness is a warm gun. Did I mention how much I HATE auto-correct on this blasted tablet.