Many years ago, I came into possession of a SMLE, cheap and rough (don't ask which model, I can't remember) that had been chambered for the 38/55, I grabbed it as a project for load development etc. I started loading .375 235gn projectiles but found they were not long enough to catch on the forward tabs of the magazine, so I had to load them singly. By trial and error I loaded 255gn spire points and loaded them with a bit of length to catch on the tabs at the front of the magazine to hold them in the magazine. I could have bypassed this problem by relocating the forward tabs, but simply didn't get around to it.
I kept the loads down and found the rifle shot a very tight group with open sights. After load development I found that ten shots averaged 1844fps over the chronograph. I shot quite a few feral pigs & horses before I moved it on.
The next chap upped the loads considerably and found that it handled them well.

cheers