I have a Remington 788 in .222. Was wondering if anyone knows the twist rate. Can't find anything on it. Also what bullet weight would be recommended for it? It shoots outstanding with everything I feed it out to 150 then gets squirrelly. Just wondering if the 40 grain bullet is too light and I need to go to a heavier bullet to squeeze a little more range out of it.

The 222 is not a 200 yd weapon..you can shoot a heavier projectile in hit if it will group and get a little more range,
but 200 yds is pushing it..Some will disagree because it's their
pet caliber..but hit an animal with it at 200 yds will have about
the impact of a CB cap or lite 22 short..it's loosing velocity that's why it becomes unstable..DD

Not really looking to kill anything bigger than a bobcat at that range. But it's cheap enough to shoot that I'd like to see what it'll do at range.

222 is one of the most accurate cartridges around, so much so that the BR guys used them for many a year. For you are wanting to do the 222 will be perfect. As far as the factory twist goes I cannot help besides advising you to run a tight patch through the barrel and measure it yourself.

788 Factory .222 was 1 in 14 twist.

So...a .223/5.56 must not be any good either?

^^First off, that's all nonsense^^
A really good friend of mine kills prarie dogs, dead, with a .22 hornet beyond 250 yards in panhandle wind. The Hornet doesn't have near as much punch as the triple deuce.

OP,

Put a dry patch on a cleaning rod. Engage rifling, mark the rod (at the action preferably) mark the bearing, push the patch until it makes one revolution on the bearing, mark the rod again where it meets the action. Pull out the rod and measure the distance between the marks on the rod. That's one revolution in ___inches, a.k.a. twist rate.

1-14". Made to shoot light bullets at about 200-250 yds. Usually won't stabilize heavier stuff than about 55grs. YMMV