You should get the mini gun for bastion. The minigun is a slow weapon but with bastions high health and shield it works. 

Save your acoins. I have the 12 and it's really only usable on eclipse since it's immune to the mech turn rate debuff (makes it slow to move) when in stealth. Besides that, there are better weapons to use and with implant removal discount gone, it's cost prohibitive to switch out implants for another weapon to make it effective so I don't even use it anymore. There is also the issue of facing guardian, which a lot of players use. It shuts you down and you're reload time is over 15 seconds. Not desirable in most situations.