The shoulder mounted machine gun is similar to the minigun, but with a slower rate of fire and the bulk of the weapon resting on the user's shoulder like the missile launcher. Due to its high damage per shot and good rate of fire, it is the most effective 10mm weapon in the game if you don't need the lower Strength requirement and silence of Gun Runners' Arsenal's, Sleepytyme (or if you don't have the Gun Runners' Arsenaladd-on.). However, it can be difficult to maintain, as only other SMMGs can repair it even with Jury Rigging, and it is extremely expensive to repair unless you have a ready supply of weapon repair kits. Alternatively if you found the 1st rank of ED-E's upgrades, repairing this gun isn't a problem.
The shoulder mounted machine gun can fire a total of about 3995 standard rounds, the equivalent of 67 reloads, or 54 reloads when modified with the extended magazine, from full condition before breaking. When modified with the mechanical upgrade, it can fire a total of about 4995 standard rounds, the equivalent of 84 reloads, or 67 reloads when modified with both the mechanical upgrade and the extended magazine.
xbox360 Picking up one in lesser condition than the one in your inventory may replace the one you already had with the more damaged copy. An easy way to prevent losing the SMMG in better condition is to equip it before picking up the more damaged one. Keep it equipped until you give it to ED-E or use it for something else.