At the moment, items only respawn at server restart.

But anyway, in my opinion, there's many military bases and other military buildings, like at airfields, that it shouldn't be too much of a problem finding an M4 sooner or later.

And finally, I personally don't like people getting armed to easily. This creates a lot of people starting to kill other players, because they're bored already.

In my eyes, finding a firearm should be something special so you actually care about your weapon and do not get into a firefight just for fun.

Regards,
Johnny