[wyop]

I'm going to address the failure to lock open on the last round issue first.

Causes for this on an A-5 are:

1. Worn or broken carrier dog.
2. Broken, weak, missing carrier latch spring.
3. Failure of carrier latch to catch.
4. Weak recoil spring. You could also have a square-stock recoil spring that is dragging on the magazine tube.
5. Improper setting of recoil friction rings (which you've already addressed).
6. The carrier latch is worn and is sliding off the surface of the carrier.

Without having the action in front of me, that's about all I can offer.

I would first look closely at the carrier latch.