The claim that there's no action noise from a bolt gun is not really correct. There IS noise when the bolt is operated, furthermore that noise is accompanied by the movement of your hand as you work the bolt. Whether this is significant depends on what you're trying to do.
For most feral animal control it doesn't seem to make any difference, but when hunting squirrels I've found the semi auto to be far superior, assuming that it has the accuracy needed.
Imagine a scurry of squirrels gathering nuts in a small grove of hickory, suddenly there's a quiet "phfut" sound and your squirrel buddy Carl falls off the limb he was sitting on. Everybody freezes instantly and begins to really listen and look around trying to figure out if something awful happened to Carl, or if he's just been eating fermented berries again.
Now at this point the hunter with a semi auto can very slowly move his muzzle an inch or two, draw a bead on another squirrel and fire.
The bolt gunner however, has to slowly move his hand to work the bolt, there's a little "snick" as the handle comes up and cocks the action, accompanied by the slightest of hand movements and ALL HELL BREAKS LOOSE IN SQUIRRELTOWN! Now instead of your targets being as still and quiet as possible, they're doing their best to get the hell outta Dodge as fast as they possibly can while keeping a tree between you and them.
Heck, even if you had a Saiga 12 with a 20 round drum you probably wouldn't be able to bag any of 'em.
The point I'm trying to make, is that several small sounds, all happening virtually at the same time, are gonna be less likely to spook a squirrel than several slightly quieter sounds spread out over time and accompanied by movement.
A bolt lock can make a semi auto rifle every bit as quiet as a bolt action, but there's not much you can do with a bolt to keep from moving your hand, except use it as a single shot.
I've said it before and I'll say it again, take a semi and a bolt rifle with equivalent length barrels, both threaded to take the same suppressor. Then walk 40 or 50 yards away and have someone fire single shots while swapping the suppressor back and forth between the two guns. The shooter numbers the shots and writes down which weapon fired each shot and the listener does the same. If the direction and angle of the shots are varied a bit (and the listener doesn't cheat by looking at what's being fired), you'll be hard put to get any real correlation between the two lists.
This test only applies if normal steps to control noise, such as a plastic buffer and a little grease have been applied to the semi auto to keep it from "clanging" after each shot.
I'll try to get some pics taken of my cheapo magnetic bolt lock and post 'em. I just wish I could figure out how to post real pictures rather than "thumbnails", is it even possible to post real pictures from a smartphone?
