Expression Lines:
Replace the lines of the M4 in weapon.dat, located at (Place your GTA SA / GTA San Andreas / data) 
$ M4				INSTANT_HIT	40.0 90.0	356	-1		5	riflebad	30	 30		0.74 -0.04  0.13    0  0	0.45 0.9 	 6 10  7	 6 10  7  99	7001
$ M4				INSTANT_HIT	45.0 90.0	356	-1		5	rifle		30	 30		0.74 -0.04  0.13    1  200	0.65 1.0 	 6 10  7	 6 10  7  99	7011
$ M4				INSTANT_HIT	50.0 90.0	356	-1		5	rifle		30	 30		0.74 -0.04  0.13    2  999	0.80 1.1 	 6 10  7	 6 10  7  99	7031

Sounds of weapon:
Replace the sound_004 and sound_005 with the Alci's SAAT GUI FrontEnd 1.0, located at (Place your GTA SA/GTA San Andreas/audio/SFX/GENRL/Bank_137)

Attention: 
Installing the sounds of the M4 will change also those of Ak47
