This is a problem that has me scratching my head. I have a CZ-52, NRA VG or better, with two issue magazines. From what I can tell, the pistol hadn't even been fired enough to work the moving parts in before I got it. I'm firing milsurp ammo out of it. This is where it gets strange. Intermittently, not even as often as once per magazine, I have a failure to feed. The slide strips the round out of the magazine okay, but then fails to fully chamber it. What's worse, the slide either locks up or sticks when it does this. The procedure I've evolved to deal with it is to drop out the magazine; smack the rear of the slide with the lock from the pistol case (hitting it with the hand won't do it, and the slide WILL NOT retract to the rear to eject the round), and after the slide goes fully into battery, to fire the round. Spent cartridge ejects normally and with great vigor. Reinsert the magazine, cycle the action, and continue shooting. It does this with either magazine. It does not do it at any one point in the loads remaining, such as with every fourth round. All the ammo looks sound and is not gritty or anything like that. I've field-stripped the pistol for cleaning and have followed the instructions in the online manual for cleaning and lubing it half a dozen times, and the problem persists. I've polished the rails and the grooves with Simichrome. I've tried half a dozen different lubes, from Gunzilla to silicone to lithium grease, and it still does this. I've run close to 500 rounds through it, so by now it can be presumed to be broken in; yet it still continues this irregular failure to fully feed which results in a jam. Anyone run across this problem before? Has anyone got an idea as to what I can do to fix this problem?