Server Tick rate is the main factor. Competitive MM is at 64Tick per second, while SOME private servers are at 128, the entire community cries in terror that Valve hasn't updated the servers with the proper rate.
The issue with this is, if you're spraying a gun, and the server is at 64T per second - it will only register so many of the shots, when the game and the server are talking 64 times per second. Now if you double that you get much more registered shots.
You can use
to view how your shots are hitting your target (can't remember if it requires sv_cheats 1 though).
I believe what you're asking is about damage and what affects it. Apart from recoil and hitting your target, there's also damage falloff, weather or not your target has armor, and where are you hitting your target.
If your target has armor you will, respectively, do less damage to them. So 90DMG per 5 hits might be normal. This is a good armor video, also we 've talked about it here.
The next thing that affects your weapons effectiveness is distance. Something like the AK is one tap HS at any distance BUT pretty much all of the SMGS are much more effective at close distance rather than battling with someone with AWP or even AK, they'll do much more damage to you at any distance.
The last thing on this list is where are you hitting your targets. Shot to the head with a MP9 at gunpoint would be a kill but to the leg you'd only do 19DMG
THIS seams to be a great table for what I'm talking about. You can see different values for different distances and with or without armor.