Just bought a Single Shot Inc HI WALL in 38-55. I'm using 255 grain cast, with gas checks, cuz that is what came with the rifle. I can only get 46 grains of FFFG in the case. I expected that as they are modern solid head cases. So far liking duplex loads. What are your suggestions? Loads?  In the cold duplex is best because the lube freezes in the bore and a dirty frozen bore really tears up the bullets. I'm using SPG lube, I've had good luck with it in my 45-70's. I'm getting a nice lube star on the muzzle. Today I used straight BP 46 grains, with a CCI Mag primer. Not a bad 50 yard group. Better was 46 grains of FFFG boosted by 3.5 of 4759 4" at 100 yards. A primer charge of 5 grains of 4227 was not as good. It was snowing and overcast and these old eyes were having trouble with the brass front sight. I'll get a target front sight next pay day.
I read a post about Single Shot Inc. that said they used two different barrels, my SN is 1047. Does any one know what barrel I have? Be glad to to hear anything about the rifle or loads.

It's really big.

They were in business for three years, and manufactured approximately 150 rifles before selling the business to C. Sharps, who continued making the rifles is my understanding.

Your right about the sights being changed. The man I bought it from wanted to hunt with it so changed the front sight. I do not know why he changed the rear. He's looking for the original front sight. Any load data would be helpful. Thanks for the info.