Your mention of the CCI .22 Mag ammo caught my attention. Saturday I was out shooting. I shot for the first time a .22mag sportster that I bought from Dogmann here at GBO. It is in like new condition. I was shooting a 50 pack of CCI Maxi Mag to sight in a scope I had mounted on the gun. Out of 40 rounds that I shot, I got a Failure to Fire on about 8 of them. All of those except one fired successfully on the second time I cocked the hammer and pulled the trigger (without opening the breach). The one that failed to fire the second time and the third time was removed from the firearm (after a lengthily wait for a hang fire), there was a good indentation where the firing pin had struck the cartridge. I rotated the cartridge and placed it back in the chamber and it fired the next time the hammer hit. This rifle has a relatively heavy trigger pull and I was very conscious of trigger pull follow through. After I was on paper and close to being sighted in I shot for groups. Not good, CCI Maxi Mags were grouping about 2.5 to 3 inches at 100 yards. Then I tried the Winchester Dyna-point, Fiocchi, and another brand. None of them grouped better than 2 inches. I had my friend try to shoot a 5 shot group and it had a wider spread than mine, 5 to 6 inches, so I felt like I was doing my part. The .22 Hornet was shooting Quarter size groups at 100 yards. But the only FTF was with the CCI Maxi Mag (of course, I have 10 boxes of it). I believe all of the ammo was purchased about the same time about 4 to 5 years ago except the Winchester which was recently purchased. I have the other .22 Mag that I got at the same time from Dogmann, I haven't tried it yet. But it will go to the range next time and see how it fairs with the CCIs.
I am going to give it a good cleaning and some JB Paste and then some more shooting to see if the groups get any better. The "O" ring fix did not effect the group size. In about a month or two, I'll send it back to get checked out and have all of the usual stuff done, trigger job and another rimfire barrel or two or three fitted for it.