Good to hear, sort of, this is actually my backup plan since you clearly at have far less experience with more realistic models at best.
How about the model proportions? It'd have to fit into a HL2/L4D character's hands. You could use Kali's CSGO gun pack for reference (and also take some parts from) since I imagine the proportions to be around the same as CSGO's M16 with an M4 stock (the bit at the back that rests against the user's shoulder, also you can probably just straight up take the CSGO M4 stock and use it for the gun, that was my plan for sight bodygroups).
Actually, do you know anyone who can do a more HL2/L4D style model? I did ask some modellers who are better at this sort of thing but they're busy.