I had a problem with a brand new 1894ss where it would do the classic 'Marlin Jam' with one particular brand of .44 special, Winchester Cowboys. Longer OAL rounds fed fine but not the Winchesters!
Anyway, after reading your excellent forum I could see that the carrier needed to be adjusted so it didn't go so far down, letting the rim of the next cartridge past and causing a jam. As it's a brand new gun there is no wear but I'm in the UK and didn't fancy waiting months to get it sorted so after reading about heating and bending the carrier up a bit I decided to give it a go.
I was bit worried about overdoing it, or snapping the carrier so I came up with this method, using a vice which gives a lot more control over the bending process and the ability to measure against the jaws of the vice to see how much it has bent using calipers or rule.
Anyway, I am pleased to say after a couple of tiny tweaks my Marlin now cycles all the loads I have tried perfectly! Thanks!
If anyone is interested, here is how I used the vice to bend the end up, probably only 20 thou or so. Hope it is of some use to someone.
I used two large screw drivers to act as bending pivots, heated the part up at the end (not red hot, but sizzling hot) to minimize the risk of fracture and gently applied pressure using the vice until I could measure a change at the end between the carrier and the vice after backing off the pressure (to allow for spring-back)
The problem loads were the Winchester .44 Special (top) with flat nose bullets. Probably to do with the smal OAL?