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The 1-7 will do fine, especially if you use long bullets and load concentric ammunition, however, the AR platform cannot use the 1-7 twist very well because the magazine precludes the use of the really long bullets.
The thing with stability is you have to spin fast enough. Once you’re spinning fast enough to be stable, you’re stable. Spinning faster does not make you “more stable”, nor does it make you less stable. Stable is stable, and anything over the bare minimum RPM is on THAT side of the fence and you’re golden.
The problem is that nasty little thing called centrifugal force. As the RPM goes up, so does centrifugal force. The best way I can explain it is by comparison to a football being thrown. Too slow a spin, and the ball goes end over end. Too much spin and it starts to wobble and loses distance. The laces are the reason it wobbles. If the ball were perfectly balanced you could chuck that pigskin and spin the fool out of it. I’m sure you noticed the inherent sweetness of the Nerf footballs kids play with? Those puppies just seem to pencil through the air and are ever so easy to get thrown straight no matter how much spin you put on them. The reason is there is far less imbalance for the centrifugal force to get ahold of.
Our ammunition is no different. Using cheap bullets and firing them through a rough throat and barrel is akin to the NFL football. Those bullets come out of the barrel with inherent imbalance which the centrifugal force will act on, so it behooves you to use the slowest twist you can get away with if you are shooting that style of ammunition. However, say you load premium bullets to excellent concentricity, and you are shooting them through a premium lapped target barrel? Obviously, these bullets will emerge from the barrel with very little imbalance for the centrifugal force to get ahold of, thus, you can spin the living crap out of them and maintain precision. This is like throwing the perfectly balanced Nerf football.
Incidentally, no bullet is perfectly balanced, and our cast bullets are worse than most, which is why using the correct twist barrel for the length of the projectile was so very effective at getting excellent groups at high velocity. There are other benefits to using the slow twist barrels, but kicking CF right in the shorts from the get go absolutely cannot be understated as a positive effect.
Back to the jacketed bullets, there are always compromises and prices to pay for performance, and there’s a big difference between building a rifle for a specific style of ammunition, and building it to be effective with a range of ammunition styles. If your goal is to use premium ammunition loaded with the absolute longest bullets you can schtuff in the magazine and tossing them at long range, then 1-7 is the twist you want. However, if your objective is to have a close quarters battle rifle that will eat anything from a 77 grain SMK to a gas check seated upside down and get pretty reasonable precision from anything you can get your hands on, from rag head freedom pills, to premo hunting ammo, to handloads with bargain bin rejects, then the 1-8 twist scratches the itch. If you want to limit yourself to 62 grain and less bullets, then go 1-9. If you want to stay below 55 grains, then go 1-12.
In my opinion, 1-8 is by far the most versatile in an AR style rifle.