I use 38lc hand-loads with moon clips in a GP100. It allows a little more space for ejection. If you plan of using 38 special in the same gun, cleaning the chambers of carbon ring will become necessary. I do like the long colt, shoots great. I get the brass from star line.
A fellow worker's uncle had brought back a M2 carbine from WWII. He was selling it for 500 dollars. I was too paranoid to buy an auto rifle so I past it up. Chance missed.
Like others I suspect a little deeper seating would be something to try. Long ago it was suggested to me that a finger nails width from case rim to top of shoulder may solve the problem.