While 6.5 G does have approx the same rim diameter as 7.62x39, it is [b]not the same as that of 5.45x39.The 6.5 seems like an easy one, since it shares the same bolt as the 7.62 and 5.45 x39.Apparently it is indeed [b]that difficult, otherwise the 6.5 kits would've been available a long time ago.I gave up waiting and got a Model 1 Sales 6.5 "sporter" upper that works great with "Grendel" ammo. So it seems like the engineering shouldn't be that difficult...Perhaps, but then it'd be necessary to get a manufacturer to produce the alternate cartridge. 6.5 Grendel ammo is already on the market.I originally thought the Grendel was pretty much a 6.5x39. It doesn't seem like it would be that hard to come up with an alternative if Bill Alexander won't do what is needed to get this cartridge off the ground.It's incorrect to say that it isn't going anywhere. It [b]is going, just at a slower pace than might be possible if Bill didn't retain the degree of control that he does.All due respect to the man, but he took the work others started and came up with what seems to be a pretty special cartridge-he may have a patent, but he doesn't own the whole concept, and it sucks to see such great potential not going anywhere.I don't know if that's possible, since P-Mags only work with the 5.56 case diameter.The one major improvement would be a round that would work in a P-mag with similar performance.