The "in-game" M4 is the same as an IRL M4, not an AR15. An AR-15 is a semi-automatic variant of the M4. If it was automatic, it would be an M4. It may look like an AR15, but the M4 is highly customizable, and all of them don't look the same. The current in-game M4 is modified with a different iron sight, a different stock, a different handguard, etc.

A

my god, the people who wanna prove they know everything about guns have been summoned

The in game M16 is an M16A4, not an A3. The A3 has a ribbed hand guard and and a integrated carry handle on the receiver. The M16A4 has a railed flat top receiver and a railed hand guard.

All the names are from https://www.imfdb.org/wiki/Call_of_Duty:_Modern_Warfare_II_(2022)#Rifles.2FCarbines
There are many explanations what the guns are, but one big point - All the guns ingem aren't copy iof IRL guns, but guns ingame are only based on IRL gun models, so they look similar, but may have different stats.

The X13 is more likely just a G18 with artistic license. The 19X has the short slide, but the X13 in game has a regular slide.

The Lachman guns are simply G3, HK33 and MP5. You've listed the civilian variants of the guns. The MP5 doesn't have a realistic trigger pack though.

The LM-S is more likely to just be the PSG1, again you listed the civilian variant and in this case the civilian version SR9 is just a tricked out HK91 with some extra PSG1 parts, not a full on PSG1 which is more like what the LM-S would be.

The SCARs are all wrong... the 17S is the civilian model and it's in the wrong caliber. The 5.56 version in game is the SCAR-L, the 7.62 version is the SCAR-H, and the marksman version is the Mk. 20. The original SCAR designations were Mk 16 and Mk 17 for the L and H respectively, and SCAR-16 and -17 were the civilian versions. To my knowledge the FN Mk 20 was never given the designation SCAR.

but so swats and militaries use the m4 or the ar15? if the ar15 is civilian wouldnt the m4 just be the m4

You do realize ar-15s are semi automatic

Furthermore the ar-15 is a semi auto civilian version of the m4

The m4 irl can look identical to the one on game