The main difference between me and RevGeo is that I generally center on something out around 100 yards. That's always been good enough to let me use no more than three, maybe four shots to hit dead-on at 25 yards. 50 years? Ah, these newbies!
For most deer rifles, dead-on at 25 yards is within three inches of center at 100; commonly a bit high. If the scope adjustments are decent, two, maybe three groups of three shots each puts the group-center at my usual two inches high at 100.
I commonly tap the scope's adjustment turret with a screwdriver handle--gently--to "settle the adjustment". It doesn't seem to hurt anything, and might even do some good. Seems to have, on some scopes.
I've found that with a semi-auto, it's easy to just mount a scope that has the crosshairs dead centered and shoot a time or two at ten yards and then move on to 25. After that it's a piece of cake, same as for a bolt-action. I'm lazy. And a cheapskate, too.
I'm no help about any sort of mounting kit. I just use whatever screws screws into place. Never had anything shoot loose; never over-tightened and broke a screw. Mainly, avoid, "Aw, just tighten it until you feel it give, and then back off a quarter-turn."