Took a while but I was able to beat it on Insane. The last few rounds pretty much require the Vulcan, I used the BFG as a secondary but only in very specific circumstances (using shield inside of horde). The perks I used were: Extended Range, Piercing Bullets, and Fast Shot. Basically anything to squeeze out as much Vulcan DPS as possible. I also used the Teleportation ability, I can't imagine how you could beat this game without it. Teleporting into nukes, shields, and even Quad-Damages was invaluable. In the earlier stages I focused on (in-order) Speed, Reloading, Luck, and finally Damage. When things got seriously difficult I grinded special stages, mostly round 39 for upgrade points. A great game btw :P
 "Dead Frontier - Night One"){kind=icon}
 "Zombie Madness"){kind=icon}