Marlin Model 37 Bolt Seating Problem

[Scuddersm]

[pacrat]

First things first ..................WELCOME TO CALGUNS

Such a problem as yours with and old 22 lr typically include either a cruddy chamber. Or a ding in the breech face caused by dry firing. That causes a slight bulge in the chamber under the FP location. Which usually makes that [last little bit] of chambering a round difficult. Or in extreme cases, impossible.

Have you tried fully chambering a round using just fingers? Does it go in all the way to the rim, without resistance?

22 rf is supposed to be a straight case with a nominal dia of .226" from end to end. But many actually have a slight bulge just forward of the rim.

If not one of those "typical" difficulties. It may well be your replacement "locking bolt". Do you have the original part, so you can make direct dimensional comparison?