i used to use my still working 24 volt 500 inch pound ridgid hammer drill on my 6 inch lazer. the batteries are of the old materials used so it is retired altho i can still get them for free.
having enough amps to keep the drills power up to par is key also. 4 amps works fine. i am using the same auger but turning it it with a ridgid 780 inch pound brushed drill. it will turn a 7 inch too, but 6 inch is fine.