This will be my first suppressor. From replies like yours as well as researching this site I'm starting to get a grasp of the subject. Is this not cycling with sub-sonic ammo issue why some people employ adj. gas blocks? Or am I off base? Also I've seen these really nice (expensive) ones that are not user serviceable. Does that mean they have a max round count?
An adjustable gas block allows you to completely cut the gas off to the bolt so that the action will not open at all. This eliminates the bolt noise and the sound of any gas escaping in the action of the gun. A TRULY ADJUSTABLE gas block (not just an on/off switch) will allow you to tune the cycling of your gun with/without a suppressor. Many AR type guns are "over-gassed" anyway and reducing the amount of gas going to the action will slow down the cycling of the bolt to a more desirable level. When you install a suppressor, the amount of gas to the action INCREASES and the gas block may need to be adjusted a bit to bring the bolt speed and unlocking timing down some. MOST AR type weapons will still cycle fine when a suppressor is installed.
"Non user serviceable" simply means you can't take the can apart for cleaning etc. Normally centerfire cans do not need any cleaning. Rimfire cans DO need cleaning, often. Rimfire ammo is very dirty and most bullets are not jacketed which tends to leave lead buildup in suppressors. Most makers weld their centerfire cans up for better service life, and it tends to discourage people tinkering with their designs or improper re-assembly by knuckle-draggers like me.
Any sealed/welded suppressor made by a known manufacturer should last a lifetime as long as you don't run a bunch of rimfire through it or something and clog it up.
SUBSONIC ammo- it's very quiet. It also is very handicapped by the fact that it is underpowered. In order to NOT break the sound barrier, max muzzle velocity cannot exceed ~1050 fps. Normally high-performance hunting/varmint bullets may not perform at all at these speeds. Rainbow trajectory with my 308 subsonic loads puts POI a foot lower than normal at 100 yds. Same with 223. A 55 gr Vmax that would normally explode when shot into a line of water jugs will just punch a nice round hole and the bullet could probably be re-used. Many bullets intended for normal high velocity use will not stabilize at these slow speeds and may come out of the muzzle with enough yaw or tumble that they will cause a baffle strike and tear up that expensive suppressor. Unless you have a semiauto specially set up for use with subsonic ammo only, the bolt carrier will only open slightly-the ammo does not have enough power to cycle the gun. Subsonic ammo, in my opinion, is better left to the bolt guns. (subsonic .22LR is another story entirely and will cycle every semiauto I own)
The supersonic crack is louder than most people (myself included) think it is, but it is something you'll have to put up with if you want all the performance your weapon was designed to deliver. When you fire a 22LR high velocity round, you hear a distinct crack that seems almost like an echo coming from downrange. This portion of the sound seems to follow the bullet away from you-and it does.
To learn more, I stood behind a huge oak tree near the 100yd targets on my shooting range while my trusted buddy shot my AR type 308 with my suppressor. I did not hear any sound at all from the direction of the shooting bench. ALL the sound I heard came from the nearest point where the bullet passed by me. It sounded just like somebody standing near the 100 yd targets (about 20 ft away from me) had shot a 22LR. The sound of the bullet's passage likely drowned out any sound coming from the area of the shooter--this is why they say one of the biggest tactical advantages of a suppressed rifle is not being able to pinpoint the source of the shot. And it would also explain why deer act so crazy sometimes when they are shot at and missed. He just heard a supersonic crack right under his belly or behind his ear-(WTF?!)-and the distant muzzle blast of the shot takes secondary priority if he heard it at all.
ETA: I'm writing all this in an effort to assist you in making your decision. Many folks enter the suppressor world with false expectations of making their 50 BMG Hollywood quiet by stretching a baby bottle nipple over the muzzle. When I fired my suppressor for the first time I was disappointed, and it took a lot of shooting and experimenting afterward to realize that my suppressor was actually doing an outstanding job of muffling the muzzle blast. What I was hearing was mostly the bullet noise.