I had a Marlin Cowboy 336 in .38-55 for a while. Friend of mine owned the same rifle for a while. I don't recall now which of us had it first, for a couple years we shopped the same store and it seemed like we bought whatever the other one just got rid of though we never did any direct exchange.
Anyway, mine wouldn't feed smoothly with the RCBS cast bullet, seemed like too much "cheek" up front. It did real well with the Hornady 220 grain JFP both feeding and accuracy ... sub MOA launching them with 3031. It'd shoot MOA with WW factory ammo as well.
Like shoot4fun said, might want to slug it especially if it's an older gun. .38-55s are notorious for bores from .375 to .380. Gotta get the right diameter bullet to match your bore.
