Burris FF mount for Marlin 336 + Burris Fastfire 2 (Yes, 2) = you'll thank me later! Get the gun drilled and tapped. You won't need to change the battery but every 2-3 years as long as you don't leave it on all turkey season..lol. I've used an FF2 since 2011 and can tell you they're tough as nails. Oh, and in the event that you need it, Burris has top notch customer service!