I am putting the carrier in first with the action closed, hammer cocked, safety on and still it will just not go in. Should I file down the side of the trigger plate? It was very hard to remove too.
Don't own an 870 but I do have a 7600 pump. Same problem. For me it just took patience. Go have a beer, cool down and try again. I know this is not a lot of help, sorry.
No, you don't need to file anything down. The trigger group is supposed to be tight, so don't worry. Make sure front pin guide is centered in the trigger group (meaning it is even on each side), and the trigger group should slide in.
Slide it in from the back to front. They normally won't just go in like I think you have been trying because of cartridge stops. What I do is start the carrier in from behind the stops and then slide the tg up into postion.
