Hi
This is a pretty fair place to ask a question, the biggest draw back is that some of the information may not be accurate (in detail) and you can get information overload real easy if you aren't a firfearms enthusiast.
Most of the major points have been well covered by one poster or another, here's my list,
Slide locks back when gun is empty.
Yes, on many handguns, but not on all. Smaller "pocket" autos seldom have that feature, unless they are a "compact" version of a larger gun that does have that feature. If you character is using a small pistol (.22, .32,.380), most models won't lock back. If using a service type (9mm, .40, .45) most all guns will lock back. Only the very cheapest won't.
Silencers remove all the noise
False. Silencer (a trade name for an early suppressor) remove the muzzle blast. Revolvers, with a small (.006+_) will let out a surprisingly loud bang, even with a silencer attached. That's why nobody does it in real life. It is only done in movies and TV where the writer doesn't have thre good sense you have already shown by asking a question here.
Autoloaders with moving barrels (recoil operated), which is most 9mm 40, and .45s can have reliable functioning impaired by a silencer. Guns can by modified to work with the silencer, but this takes some work by someone who knows what he is doing. Not something a gangbanger was likely to have access to. Just getting a threaded barrel and screwing a silencer on it will not ensure the pistol will work reliably. It may. It may not, and may need to have the slide manually worked for each shot.
Blowback autoloaders (smaller than 9mm caliber) usually have fixed barrels, so the weight of the silencer is no concern to functioning.
There is a bit of noise that comes out when the case is ejected, but it is not very loud (handclap).
Speed of sound = 1068fps at sea level. The term subsonic load means below this speed. In a round that normally exceeds this, it is a special load intended for suppressed use. Usually uses and extra heavy bullet to make the most of the slower than normal speed.
Also, the bigger the caliber, the bigger the silencer has to be. One that actually works for a 9mm will be close to 2 inches thick and round 6 inches long. And the hole goes throung the center, so the bulk of the silencer blocks the normal sights.
Since you said "inside a hotel" I left out a few comments about rifles.
If you want the closest thing to absolute quiet, you would put a silencer on a gun with a manually operatred action. Single shot like the T/C Contender, a sawed off rifle (Bolt, lever, anything but an autoloader). Thissetup can be made so the about all you hear is the "click" for the firing pin falling. The British built small numbers of a modified SMLE rifle (bolt action), in .45ACP with an integral silencer for taking out German sentries. Very quiet. The other thing that could be done is to fit a standard auto pistol with a special lock to hold the slide closed. The VC had some pistols like this, for assassins.
If your shootout hotel is a modern nice hotel, the walls are pretty good, and a properly suppressed handgun will not be heard over a loud tv. In a cheap place with paper thin walls, people next door could hear something (maybe) but wouldn't know what it was. An of course, if the tv is turned on, chances are they wouldn't notice anything.
So, how is this for information overload? Hope it helps. Comeback often, the high road can be the road to enlightenment.
