I don't hear the firing sound twice
It's a looping sound, which almost never actually correlates to the amount of rounds you fire. I don't understand why they started using looping gunfire sounds; they're awful compared to playing a sound for each shot of a full auto burst.
It's was alright on the MP7 when they first did it, because that's 1200rpm and it's extremely hard to fire only one shot with it anyways, but with the lower RPM MP5 and M4, it becomes practical to try to fire one shot at a time, and when you try that, you just hear the "fade out echo" that's supposed to play after you fire for a while, no gunshots. It seems to be a pointless step backward in quality from the other weapons' nice sounds that actually indicate how many rounds are fired.
it always instantly fires 2 bullets.
I take it this is from experience in single player? In single player the looping-sound full auto weapons (m4,m4203,mp7,mp5) are bugged, firing the first two rounds of a burst at exactly the same time. You can't fire a single shot unless it's the only one loaded. I tried firing a single round for about an hour and it simply can't be done.
I did find that you can actually utilize this to fire the whole mag almost twice as fast as a regular full auto mag dump. The frantic clicking makes my aim suck, along with the extra recoil, so it's not very useful, though.
In multiplayer, you can take a single shot with these weapons. The higher the rpm, the harder it is to do consistently without distracting yourself from aiming, though.
Lower RPM would make single shots on the M4203 easier, and thus make it
less useless, yeah, but a more thorough revamping of it could make it
properly useful instead. What I had in mind was if the M4203 be changed into a semi auto, get a 1.26x headshot bonus, (just enough to decap trash on HoE) have a capacity reduction to 20, and an ammo reserve reduction to 200. I think this would make it very suitable for very deliberate usage on all difficulties while not being overpowered.
Alternatively, lower recoil could make double-tapping heads more feasible, and balance out the M203 to usefulness. This would also be realistic; the added weight of the M203 hanging off the front of an M4 does tone down its muzzle rise.
And yes, Pipes/M32/M4203 all on slot 4 is a bother and fixing that should be a high priority for TWI.
But not as high as making a single .44 weigh 2 again, but I digress.