He's Right.
This is the forum you should be asking Questions in, but I will anser your Q's here only if you ask any other ones in that link.
1: The sentinal Beam isn't in Metropolis
2: Seeing there isn't a Sentinal beam, make the SMG a jetpack by doing the following:
Go to Damage Effect Branch
Go to objects\weapons\rifle\smg\damage_effects\smg_trigger
Give it a force of about 3
To get infinate ammo and no overheat you can get a trainer wich I don't think im allowed to say, look for a PM with a link.