sections could be connected in any equivalent manner such as friction fitting press fitting or counterbolt fitting the shell casing 20 also contains a passage 21 axially located which goes through the shell casing passage 21 allows the light from light source 24 to pass through shell casing 20 shell casing passage 21 terminates at a center tip 22 of shell casing 20 shell casing 20 is substantially similar in shape and length to a standard cartridge for a gun of the caliber being sighted in this is so that the shell casing will fit with close tolerance in the chamber and also so that it will not cause any damage to the inside of the gun by being the same length as a standard shell the shell casing also will have a high degree of stability inside the chamber of the gun 10 the advantage is that the shell casing will be supported for its full length and will not have any wobble one material for shell casing 20 is brass this adds the advantage of being malleable and easy to machine yet hard and relatively inexpensive brass is a common choice of shell manufacturers for the same reasons as noted above however those skilled in the art will recognize that other materials can be chosen based on need and economics fig3 a and 3b show a view of an interchangeable muzzle tube system one of a plurality of interchangeable muzzle tubes 30.