Played with 40-90 sharps straight, not a fun cartridge.
Replaced barrel eventually.

Read Ned Roberts' thoughts on the 38, 40 and 45 express cartridges in The Breech-loading Single-shot Rifle. From what I remember he went from the 38 to the 40 and then the 45 and liked the 38 best,

Looking at one. Factory load was 217 gr bullet and probably has something like a 1-54 twist, just a guess. Can be made from .405 Basic brass necked down. Must be a reason they were only made 4 years.

I never heard of a 38-55 Express. However once Winchester and Marlin I think  produced 38-55 Loads that were listed as High Velocity loads with Jacketed bullets. I am not sure how long they made that ammo but after WW2 they did not re-introduce those loadings. I suspect that the existence of many Black Powder Barrels came to the factory attention and they decided not to push that issue. Recently their have been loads listed for 45-70s that would be considered way to stiff for Trapdoor and or other Rifles with Mild steel barrels. I do know some Long Range Black Powder enthusiasts have tried to get Long Range loads with .38 Caliber rifles with not much success.
Does not mean it cannot be done but I suspect the issue is (Traditional Cartridges) Just another thought on this subject. FITZ, OLD TUCK

Fritz, I only asked because a number of years ago I bought a Stevens two barrel set, one heavy barrel with a 14" twist and the other a light barrel with a 20" twist that the seller said was an express. Said he could to shoot not get either barrel  to shoot anything heaver then a 250 gr bullet, which I have proved him wrong because I have run 310gr bullets in both barrels with good results and the heavy one is my go to gun out to 500yrds.