First,the rifle idea is like which person attracts you or which dog do you like.It does not HAVE to make perfect sense to anyone but you.
And no matter what you would like to build,you will always find some folks who will tell you its a bad idea. Sometimes they are even right!!
And there will always be people who will tell you to spend your money to build the rifle they WISH they could build....but don't.
My 2 cents. On its own,the 250 Savage AI is an interesting idea.It would be a surpringly efficient delightful antelope and deer rifle......IMO up to about 350 yds.
I've hunted with a 257 AI for over 20 years.I love it. Longest shot was 430 yds.Aimed at boiler room and hit a neck shot.We can't really know what breeze bullet will fly through over a quarter of a mile of air,and even a 115 gr Ballistic Tip is not the best wind bucker. A BC of .430 and 3100 fps is a bit better than what a .250 AI will do. I make no claim to being a wizard at reading wind.First round cold barrel wind estimation in antelope country gets more "iffy" by a lot with each 100 yds past 300.Its really "iffy" at 600.
FWIW,aiming at the heart/lung and hitting the neck was luck. Luck can go either way.That shot gave me a dose of reality.
I suggest studying the long range ballistics. See what the numbers are at 600 yds. If you talk with most hunting bullet manufacturers,someplace around 2000 fps is minimumto get them to expand and perform.That is also about minimum velocity for temporary cavitation to begin to be a factor in trauma.
So see how faraway you have 2000 fps + and that might be the limits for good game performance.
I wasn't there for the 600 yd shot with the 100 gr bullet. Maybe true.Far more 600 yd shots are claimed than made. Was it lasered? Estimated?
I'dseriously take the 600 yd capability with a grain of salt. Its a very good 300 yd cartridge.Maybe a bit more.
If you want a 250 AI,go for it! Have fun! It will be delightful.
Consider, the bullet manufacturers don't put a lot of resources into 25 cal. I really like the 115 Ballistic tips.IMO,about the best available.Its real good.
But there are better long range bullets in 6mm and 6.5 mm. .244 vs .257 vs .264. The 6.5 is only .007 larger. If I were doing it over...I'd think about that.
The 6.5 Creedmore is up and coming. Starline is making brass.Its used at 1000 yd target shooting.Its about the same package as your .250AI.
In that M-70,a standard +P 257 Roberts load will probably give you the ballistics of your .250 AI. Brass might be a little easier and no fireforming.Still a fine,unique "classy" round.
But,doggone,a .250 AI is a fine idea.Follow your own trail!!