Gatofeo,
I used to have two Universal M1 Carbines, and they both shot fine sor several thousands of rounds.
HOWEVER, I have seen and examined several problems with M1 Carbines in the last 30 years that had excessive headspace, and gave case separations as you described.
That .30 US Carbine round is really a pretty hot pistol cartridge, and headspaces off the case mouth/chamber lip like the .45 ACP and 9mm Luger cartridges. Improperly trimmed cases will give excessive heapace, OR, worse, overly long cases can be forcefully chambered, and when fired, will push chamber pressures thru the rooof! I examined a few cases that actually left 1/4" - 3/8" brass flashing in the chamber throat after firing. All the signs of excessive pressure: flattened and cratered primers, buldged case heads, case separations.
You might want to do a chamber casting to see if the forward part of the chamber/throat area is damaged.