I have an old Marlin 989 (detachable clipazine, predecessor to the 795, I think).

Problem is, the thing won't fire with a mag inserted. Mag out, shoots fine. With the mag in, it'll feed rounds if I cycle the bolt, but when I pull the trigger, click - no bang. I replaced the old action with an action I found on Numrich. Any ideas as to what could be causing this? Only things I haven't replaced are the bolt and extractor and recoil spring.

Thx

I had the same darn thing happen on the M70 that I had..... I checked the bolt clearance/interface between the action subframe and the bolt and receiver. They were so tight that the bolt couldn't run all the way forward. Well, I adjusted the bolt/lower action clearance by lightly filing the top of the action bars until things were smooth and the bolt was going forward all the way...but it didn't solve the same problem you are describing... turn out it was the recoil spring itself. I found that the recoil spring was too weak and not driving the bolt far enough to let the extractor slip over the edge of the rim. This only happened with a mag inserted (mag was causing extra resistance on the bolt), and manual cycling a round let the bolt slam hard enough forward to slip the extractor over the rim. Got a brand new recoil spring, squared the bolt face with a machinists finish file (bolt face was a little rough from the factory),  polished some of the internals, and it all works fine now with or without the mag inserted.

Hmmm...that might work. I vaguely remember that spring getting kinked at one time when I replaced the stock.

Finally replaced the recoil spring and got a chance to take the 989 out and run it. Here's what's odd - it runs sporadically. Sometimes, with a mag in, I can get a string of 4-5 shots before a FTF (fire), eject mag, cycle bolt, pull the trigger, bang. Put the mag back in, cycle the bolt, pull the trigger, click. I've tried CCI, Remington, Winchester...it seems to run well on CCI, not so much on Rem or Win (no surprise there).

I noticed that, when I eject the mag and cycle the bolt, the round sometimes stays in the chamber...extractor problem, right? Why would that be causing these misfires?