I repainted the m4 and it seems to have fixed the fps issue.

Edit 1:(My M4 was originally painted black, I took the magpul buttstock off and painted it, then took the magpul handguard off and painted them both green. Then painted the body green and reattached them.)

Edit 2: The above fix is only temporary, it seems every time you log in you have to spray paint the rifle to get it to stop flickering.