Sorry if this is one of those questions some of you get tired of seeing... All I can say is "one should never get tired of giving someone else knowledge." I'm looking for a 600 yard AR 15 for 200 to 300 lb whitetail. The .300 OSSM looks cool, I just wish there was a 6.5 or 7mm option there. Again though, I would like the advise of someone with more experience. I have 14 years of military and law enforcement, so I am not inexperienced with the AR, but these newly available calibers leave me guessing. Any help is always greatly appreciated. I know this kind of performance is easily achievable in an AR 10, but if it comes to that, I'll just stick to my bolt guns. P.S. I like to hit a deer with about 1000 preferably 1200 ft-lbs. So I don't think the Grendel is gonna get it done. I think one of the SSM's is going to be my only option, but that's why I'm posing the question.