I own two of the Stag Model 6 Super Varminter with 24" 1:8" Stainless barrel. I have shot it off a bipod in NRA F T/R at the Berger SW LR Nationals 600yd MR course, and found it highly adequate with the Bob SLED magazine replacement. It was superseded by the
Stag 15 Varminter which is, to be best of my knowledge, simply the same gun with a different rear stock (and no accuracy guarantee). My second was built from the factory kit, and performs identically. I bought the first one (guessing) about a decade back. It's always been ready when called upon and displayed no teething pains.
It came with the 1/2MOA (with factory match ammo) factory accuracy guarantee; and using Prvi-Partizan 75gr match, it achieved the guaranteed accuracy several times for me at 100, and at 200yd (in calm conditions).
I like the rifle despite its obvious greater weight; off a bipod, the weight is not much of an issue for me. The factory two-stage trigger is the only two stage I own, and I especially like it. The lower is my basic foundation for all my other Uppers, and that trigger makes all of them all nicer to shoot. One of them has the Luth AR MBA1 stock, and it's a godsend with its adjustable LOP (I adjust most of my rifles to a 16-16 1/2" LOP due to my 6 1/2ft height). But the adjustable cheek rest is too high for me even at it lowest when mounting scopes in standard one piece base/mounts. I removed mine completely.
The 1:8" twist is fine for 75gr Hornady HPBT-Match, and that load (23.5-23.7gr Varget) does well in both 1:8" 24" and 1:9" 24" barrels of mine. I am planning to test IMI 77gr Razor Core soon, and expect I it to do fine.
My only 1:7" twist barrel is in a 16" Upper and I will be testing it soon with the IMI 77. I would not try it with the longer ELD type bullets; but really, if we keep the rifle to 600yd, they're not actually needed. I'm generally a conservative regarding projectile stability.
The Stag Model 6 (and I suspect) Stag 15 Varminter are my best idea of excellent rifles for getting into MR (and maybe LR) AR shooting with the smallest overhead or hassle. I don't shoot LR (to 1000yd) with the AR. I honestly believe it's best out to 600yd (and maybe 800yd), and use my 28" .260 for out to and past (1100yd) LR distances. I like a velocity margin at those distances.
I just acquired
a 20" 1:8" 6.5 Grendel Upper, and that could be a good rifle as a bridge between the MR and LR.
Greg