The Mounts arent the same, If the regular mount was that easy the real m203 would fall off the gun from a 40mm launch. The lack of m203 groove in the barrel makes it an issue and that SEAL likely copied it from an Israeli system, as they are the only others who do shorties with m203s.
If you look at the pic there is no ambient light shining between the CQBR and M203
mount area
Israeli Mount.
