On my m1 carbine I found the feed ramp with machine ridges on it, full metal jacket ammo would feed well, but round nose it would act like a brake and stop the feed. So after looking at the copper lines that the FMJ would leave it on the feed ramp I used some metal sandpaper to smooth out the ridges and then polished the ramp and clean it then re- blued it, now it will shoot any type of m-1 carbine ammo, Now this I have only found in civilian ones not the military ones. This just if you want to shoot ammo that is not FMJ.
Other than doing 1911’s this was the most popular “Ramp and Throat Job” I used to do back in the day. Now that you mention it I don’t ever recall doing one on a U.S. rifle but I did a butt ton of Universal’s and AO’s
The first one I did was also a universal m1 carbine never had to do any military ones. But I did find a European browning 9mm high power that needed it done and still have it and works really fine and shoot all kinds of 9mm bullets with no hang ups.