My remington 223 with 12 twist will stabalize the 69 gr bullets but not the 75's. The extra speed of the 22-243 will get the 75's to stabalize but not for a long distance. After a few hundred yards the 75's will likely start to tumble.
Ive got about every twist of 22-243 middlested except 16 and 7 twist. The 14 twist barrels shoot the 50 gr bullets and smaller superbly and in fact Ive won some informal shooting matches with them.Most were impressed that I was getting 4 5 shot groups on the same piece of paper that averaged in the low .2's (@ +4300fps) The 60gr bullets and larger dont shoot as well and I havent bothered spending barrel life on those bullets. The 14 twist barrels will get the 30-35gr bullets over 5000fps but so will the 22-250 AI.
The 22-243 doesnt actually have much gain over the 22-250AI until your bullet weigh starts to get over 60'gr.
If your after a barrel twist that shoots all bullet weights, get the 8 twist but expect not to get velocities your after with the lil bullets, they generally wont make the trip especially after the throat starts getting some aligator scale. My old 9 twist barrel blew up 55gr bullets after about a thousands rounds were through it and it was getting very rough. When it was new it would shoot the 50's just fine.
I like Hart barrels but something you need to consider is barrel length. 26" should be a minimum length to consider, anything shorter is giving the cartridge a handycap. My factory barrels that I ream out generally are about 26" long but my custom barrels usually go 28".
Ive killed lots of coyotes with the 22-243. The 40gr bullets tend to splash on coyotes while the 60gr bullets and larger tend to tear up pelts. Im at my happiest using 50gr noslers. Usually always a quarter sized exit hole. The 55'gr noslers are about the same but given a choice between the two, I prefer the extra 200fps I can get out of the 50gr bullets.Average shot for my area is around 200yds but can reach out to 500yds on occasion. The 50gr bullets still tip them over at that distance depending on shot placement. Obviously headshots at 500 are kinda few and far between in most instances, Im happy just to hit them in the chest.
I got your PM. I havent been around the last few days as Ive been out on the ranch hunting coyotes. Im actually using a 22-243 right now and Ive taken 6 so far the last 3 days. I shoulda gotten more but its been horrable fridgid (too cold for the camera too) and Im finding myself sleeping in because I dont wanna get outa bed till the sun is starting to warm things up. LOL.
Anyhow, I stopped at the ranch house to clean up and thought I would check in on ya'll, gotta get back out after-em now. Hope this helps.