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Dtech or Olympic arms WSSM uppers 6.5mm, 7mm, 300?

He will make it for you in anything up to 358WSSM I believe. I know he's done the basics, 22, 243 and 25 as well as 6.5, 30 and 358 for sure.
The long bullets aren't going to happen with a semi auto. With the 243, you're limited to MAYBE the 105 Amax if you're lucky to get it to shoot at the depth that fits in the mag (which can be stretched to 2.35" pretty easy with a modified mag)

Long story short, yes...the larger calibers (6.5 and up) are really hamstrung by what bullet you're going to be able to use. Most guys are running 150gr bullet sizes with the .30WSSM
I don't know anyone with a 7mmWSSM but JARD is actually making them factory, so you could call them and ask.
6.5 is the same. The best options are like the 123 and like.
 
I have a 30/25 WSSM from DTech. Great upper. I have mine shooting 165's well. I am going to try some 150's but have been playing with my another build lately. Trying to use the stock mags with the 165's was going to be tough. I got one of the modified PMags from C_Bass and that let me get things out long enough. I shot a few 175's but stopped when I found a 165 grain load. In all it will do what I wanted by giving me .308 or better velocity out of an AR 15 with up to 165 grain loads.
 
If you're interested, I have an Oly .243 WSSM upper that has supposedly been re-worked by Dtech (bought it used, never shot it) on which I'll make you a hell of a deal.