Carbine Collectors have informed me the trigger pull was something the Government asked them to improve and the manufacturers tried to improve on as the Carbine was made. In later WWII production, they changed the design of triggers and sears a bit and got the trigger pull down a little, but never to their satisfaction.
The hammer of the M1 Carbine has a notch that controls sear engagement almost exactly like a tumbler on 18th century Flintlock rifles and muskets. The sear is likewise very similar to the sear on that era of gun locks. I long ago lost track of how many hundreds of trigger jobs I’ve done on 18th and 19th Century muskets, rifle muskets, rifles, revolvers, pistols and carbines – including original CW Smith Carbines. There are two basic ways to lessen sear engagement on the hammer, file/stone it down or glue or soft solder a shim that does not allow the sear to go in the hammer notch as deeply. Filing/stoning the hammer notch shorter IS NOT RECOMMENDED because it can easily wear to the point you will have unintentional doubles, triples or FA firing. Of course, if one Melonited/Salt Nitride treated or some kind of reheat treating the parts afterward, that would make it last longer after shortening the sear engagement, but you can’t do that and the other work for under $ 50.00. Soft Soldering/ Gluing a shim to the hammer is a less expensive alternative and when it wears out, you can glue or soft solder another shim. BUT, here’s the problem with that – it is NOT ALLOWED to be done for any CMP Games Match. I know, I have deliberately asked permission at least twice and I never got an affirmative answer. Adjusting the amount of sear engagement on the sear also requires Meloniting/Salt Nitride or some kind of rehardening. Some folks use case hardening compound and while that can work, I won’t do it because when it doesn’t work correctly – you have unintentional doubles// triples or FA firing.
Finding an early or worn trigger spring is a good idea. I also look for hammer springs that were manufactured a bit shorter, though I DON’T recommend cutting coils off the hammer spring.
I honestly can not think of a way one can work a Carbine Trigger Job for under $ 50.00 and give a shooter a trigger job that is safe and will last.
What I DO know is there have been A LARGE NUMBER of people each year at the Nationals who had someone work a Carbine Trigger and their Carbine fails the minimum trigger pull weight OR malfunctions during the matches.
What I HAVE seen is folks deliberately buy a well worn Carbine that came back from Korea and the trigger pull has naturally worn in after firing thousands and thousands of rounds. Some guys bought the carbines just to get the better feeling trigger groups and swapped the trigger groups and then resold the Carbine.
