Re: thoughts on putting a mil dot scope on my 40x22
depends on what you call "good". i would suggest to put on the best that your budget will allow, and an optic that best. mimics what you have in mind for the .308.
i am a cheap guy, and have learned that going with a cheapie scope leaves you replace it in most instances a few years down the road. there are actually some budget scopes out there that are actually semi dependable, but usually what ends up happening is the mechanicals in the adjustment housing gets worn out. this is mostly due to the heavy use of adjusting most scopes get when using on a trainer. i regularly dial for windage from 25 yards to 300 yards, so the turrets are always spinning. a better quality scope hold up to this the best.
almost by default, that 40x heavy barrel is a top shelf rifle and it almost cries out to have a matching set of top shelf glass on it. otherwise it's sort of like having a ferrari with discount tires on it.
but whether your going with a "decent scope" or just one to get by with, you should at least find one that is similiar to the one that's on your .308
in other words, if the scope your 700 is "X" amount of magnification, the trainer should be in the same neighborhood. side focus the same should be on the trainer. the same increments of adjustment should be the same between the two. all of that greatly helps the transition from one to the other. the most important features to keep the same though are the reticle and the amount of adjustment.
i'll put money that in the end, that 40x trainer is going to be your sweetheart. once you see how well it shoots, you'll probably be spending more time with it than anything else in your inventory. treat your sweetheart right and you'll get more out of it. does it need a nightforce on it?, no, but if you had the budget to do so, why not?
folks have gotten by for decades with cheapie scopes (lower end bushnells, simmons, tasco, etc.) on .22s and even centerfires without problems, but are generally just shot at one distance and never adjusted for different ranges. it's when you start exploring the potential of what a trainer can do, that the better quality optic comes into play for longevity and performance.