I have a Ruger 22 Mark III that I have been having problems with. I had other issues that I resolved by replacing the hammer bushing, loaded chamber indicator, and extractor with parts from Volquartsen.

 

The issue I have is failure to feed a round. This never happens on the first round. It probably happens 2 or 3 or 4 times per magazine. Racking the slide chambers the round.

 

I am using CCI Mini Mag plated cartridges so I don't think ammo is the issue (I have also tried Federal LRN).

 

I have also rounded the rear corner lips on some of the magazines to see if that would help but it is still getting FTF's.

 

Any ideas what could be causing this?

In all likely hood, it's the ammo. .22s are extremely finicky when it comes to what ammo they like to it.

 

I have a Ruger mark 2 that loves Federal .22 ammo, runs flawless - But when I put in CCI or Remington i get failures.

 

Other things to check would be any burrs on the feed ramp, worn springs, etc. 

How many mags do you have? Does it do it with all of them?  Where they part of the package when you bought the gun?  Try different ammo, as suggested, borrow and try different mag if possible.  Feed failures can be tied to magazines on most occasions.  You replaced an awful lot of internals, double check to see they are all installed correctly.  Get some Flitz and polish the feed ramp.

It fails to feed how? Does it go into battery without picking up a round, or does it jam somehow with a round half way up the ramp?

the other thing i've seen, especially with CCI mini mags, they are prone to more failures when it's cold outside. They have a waxy coating on them, my theory is the cold weather hardens that wax up causing issues. 

How many mags do you have? Does it do it with all of them?  Where they part of the package when you bought the gun?  Try different ammo, as suggested, borrow and try different mag if possible.  Feed failures can be tied to magazines on most occasions.  You replaced an awful lot of internals, double check to see they are all installed correctly.  Get some Flitz and polish the feed ramp.

Lots of mags and all do the same. Two came with the gun and the others were purchased separately (Ruger mags). Tried a few types of ammo. I also tried polishing the feed ramp.

It fails to feed how? Does it go into battery without picking up a round, or does it jam somehow with a round half way up the ramp?

Yes it does go into battery. It just doesn't pick up a round.

sounds to me like the mag release is holding the mags too low in the gun 

sounds to me like the mag release is holding the mags too low in the gun 

I had also replaced the mag release with a Volquartsen extended release (not to fix anything but to make it a bit easier to press). I will try putting back the original release and see if that helps.