Hey Steve!
Just joined up over here (knockemdowm elsewhere)
I have a .22-243Win that is a real nice shooting rifle. Kills the heck outta coyotes with a 75Amax in the mid 3400fps range. That is a mild load with RL-25, not pushing hard at all...
Sought to improve upon that one, and schemed up to build a .22-243AI, with a friend. We both used Brux 1:8tw barrels, and speced our chamber with a long throat and semi-tight "no turn" neck with Lapua brass.
We've found happiness with 75Amaxs @ ~3600fps and 80Amaxs @~3500fps range. H1000 and Retumbo for powder, Lapua cases. These are relatively mild loads, primer pockets remain tight after several times fired. Only bushing nk. sizing needed, and no case trimming!
Aside from the ease of loading & maintenance, this .22-243AI is proving to be all we'd hoped for! The ballistic performance of a high b.c. .224" bullet at those speeds is nothing short of phenomenal. MV is fast enough to satisfy MBPR shooting inside 350yds, and the high b.c. of those Amaxs pays dividends to as far as one would reasonably shoot at a coyote. The terminal performance is IMPRESSIVE, without being overly damaging...
I saw mentioned the .22/6mmAI above, that's gotta be a real demon! Pushed hard enough, the 22/6mmAI is likely entering the realm of negatively affecting bullet integrity. IE, "poofs" in mid-air, or "splashes" on critters. In that regard, huge overbores like .22/6mmAI & .22/284 etc. become performance constrained by bullet integrity, rather than case capacity. Every bullet has it's breaking point and too many RPMs on a given bullet results in all that wonderful performance being lost due to a compromised jacket. Combine that with the need for having a long action to feed heavy .224" bullets seated long, and the above two lose their appeal (to me)...
Conversely, short action wildcats like the .22-50AI, .22x47L, etc. need to be pushed very hard to reach the upper end of a heavy .224" bullet's velocity threshold. That leads to premature toasting of brass and torching of throats when da pedals to da' metal. The aforementioned are wonderfully efficient cases, especially for 50-60gr bullets! However, their limitation for pushing .224" heavies fast enough to be truly magical, is powder capacity. Still a 75Amax @ 32-3350 from either, is no joke! But one @ 3650 is friggin' incredible...
That is a main reason we chose to stay with the .22-243AI. Its performance window seems to be in the upper end of a .224" bullet's "sweet spot", for lack of a better term, without crossing over the line of diminishing returns from too much speed. It has enough case capacity to allow the use of slow burn powders, which keeps pressure in check. That translates to being easier on throats and more forgiving on brass, while still netting enough speed to push a .224" bullet like the 75 Amax to it's "RPM limit". In that regard, a proper spec'ed .22-243AI a can almost mirror the performance of a .224TTH, or even a .22/6mmAI...
In summation, the reason we chose to go with a .22-243AI are:
1. Can load high b.c. bullets long enough to maximize case capacity.
2. Can fit/feed from an AICS magazine at that c.o.a.l.
3. Runs from a short action, which allows for running the bolt while staying on the scope.
4. Case forming from excellent Lapua 243Win. brass
5. Minimal sizing and no trimming leads to excellent case life for an overbore wildcat
6. Capcious enough to use slow burn powders to keep pressure in check & still yield max. FPS.
7. Fireform loads in the 3250fps range are already devastating on varmints
8. Recoil is negligible, can spot impacts thru the scope
9. Incredible ballistic performance, flat shooting & wind bucking ability
10. Absolutely devastating on coyotes
The bonus that we've seen is that, on close in (<200yd shots), a 75Amax will blow thru on a broadside rib shot, leaving a manageable exit hole. Frontal shots don't tear one up as much as you'd think. Raking/heavy bone shots, all bets are off on fur damage, but that is more a factor of splintered bones. Either way, you're gonna have one heck of a meat report to listen to!
Since building these two originals .22-243AIs, I believe our smith has built at least another 8-10 for coyote hunters. To a one, I've heard nothing but jaw dropping awe & happiness regarding accuracy, ballistic and terminal performance. I haven't shot many coyotes with mine, but my results are identical with the bunch. Some of those guys are serious coyote killers and collectively have amassed quite a database of dead bodies to draw results from. Suffice to say, a fast twist .22-243AI is all that, and a bag o' chips...
Good shootin'!