I've got this old .22 rifle, an H&R Leatherneck model 150. It's never functioned quite right so long as I've had it, two magazines, both the same. It jammed when chambering a round; every time for some ammo, and very rarely with CCI Minimags. I've tinkered with it off and on but never seriously enough to really figure it out. I fiddled with mags, springs, cleaning, adjusting, etc..
Well, the other day I had it out again and was looking it over closely. I noticed that the bolt was a little on the rough side, well not particularly rough, just not machined quite as smooth as one would think it should be. I cut a strip of 320 sandpaper and polished it, then a strip of 600 grit, then 1500. It was absolutely shiny and smooth by the time I was done. It cycled much smoother, not the slightest drag.
I took it out today and it ran like a champ with whatever ammo I tried. It's funny how that works. I wonder if this old rifle has been jamming up since the 1950's when it was made?