A Remington 750 semi automatic rifle came in with light firing pin strikes. The hammer wasn't striking the primer enough to consistently ignite the primer in the cartridge. After checking the bolt assembly and firing pin, I decided to look at the trigger assembly.
Keep in mind that Remington is now defunct and parts are not available. But when the company was still in business, they considered the trigger group off limits even to a gunsmith. Unless you were an authorized warranty repair shop, that is.
Here you can see the earlier trigger group of the 742 on the left, compared to the 750 on the right. The newer trigger group is a bit thicker in the middle.
I coated the hammer with Dykem blue and worked it back and forth a few times. I discovered that the hammer was rubbing against the side of the trigger housing. This would slow it down enough that the hammer wouldn't strike the firing pin with full force.
So I disassembled the trigger group and removed the hammer.
I polished the hammer in the area where it was rubbing against the frame.
I also cleaned up the inside of the frame that had some burrs from the manufacturing of the part, and thinned the wall of it a bit to give the hammer more clearance.
I checked the trigger group again with more Dykem blue layout fluid to make sure the hammer didn't scrape against the trigger housing again. After reassembly, I test fired the gun three shots. Reliable ignition !