55's in my 22/243 AI was a no-go for the powders I chose. I tried win 760 and the accuracy node was at 3950 which was disappointing when my 22/250 AI is running 55's at 4050 fps. Then I tried Varget and blew the primers out of several cases using 55s, learning that Varget has a steep pressure curve where pressure will spike. The velocity with varget was in the area of at 4030 fps where pressure spiked.
I screwed the barrel off for a while, then went back to it a year later remembering that the 60g Sierra and the 63g Sierra would stabilize well in a 14 twist. I hit pay dirt with the 60g Sierra at 4000 fps in the 23" barrel shooting a very, very tiny group, and shot more groups to verify the load with Win 760.
I have shot many barrels out of 243 AI's on chucks, p. dogs, and jackrabbits. I used Rem brass, 48.5g of Win 760, CCI 250 on 28" barrels shoots 3800-3850 in a zero freebore chamber with Win 760. The Hart 12 twists have a wide tune load of powder charges with the Rem brass from 48-50.3g with my lot of Win 760. 50.3g is doing 4020 fps in my 30" barrel with a Winchester mag primer shooting dot size groups.
Another consideration for you is the 6 Rem AI on a 26", 14 twist barrel. My load runs 70g Nosler ballistic tips at 4100 with max at 4150 on a zero freebore chamber. I got a deal on a Douglas 10T, 26" barrel but the bug hole tune load was at 3950 fps with the same cases, reamer, bullets, powder, and primer. With zero freebore reamers, barrel life with win 760 and AA2700 is excellent, to say the least.
My best hot rods have been:
257 Weatherby with zero freebore shooting 85-87g at 4130 and 100's at 3850
6 Rem AI with zero freebore reamers, 14 twists shooting the 70's at 4100
These two above combos are the EASY button on load development, case management, with very decent barrel life. You will screw up both of the above by increasing the freebore to over .030 and putting on a fast twist...take that to the bank.
The 6/284 with zero to .030 freebore, 14 twist shooting the Nosler 55g ballistic tips at 4300 is real world from a friend who uses the rifle as a coyote rig. The two 6/284s that I had were shot out using 85g Sierra hp at 3600 with barrel life of 800 rounds, IMR 4831.
I have done a LOT of night hunting. We considered it part of the sport to coax them in closer. We hedged out bets, where legal, to use two socks with two cans of sardines in each can, hung within each side of us. Also, we tested the wind with a spray bottle of fish oil when we started the stand. When we had a coyote start to circle, we would spray the fish oil again, and most of the time, they would come in on a run or sprint. These techniques can save you a lot of grief in shooting coyotes at a longer range at night, which are difficult to find at best.
Also, target identification past 250 yards can be difficult, especially if you are in an area with cattle. I almost shot a calf once when a bobcat hung up on me. The Cat would disappear, then reappear, sit down behind a lot of brush. The calf was laying in the grass and would raise it's head from time to time with only the eye reflecting back. Something just did not feel right, and I never just shot at the eyes. I was able to use a birdcall to get the bobcat to come on in, and we ended up shooting him with a shotgun because he was so close and coming in on a hard trot in very brushy area.
