Re: 223 Ackley Improved
I Have two Hart Barreled 223 AI's set up with Match min spec reamers with zero lead for shooting 50-55g bullets. Both barrels are 14 max heavy varmint twist, one is 23" long and the other is 26" long.
You posed the question if it was worth it to go to an AI or not. If you need a repeater, then do not go AI. A Max heavy varmint 26" 223 standard with a min spec chamber, extremely short leade is a sheer joy to shoot, it is just about an idiot proof cartridge.
You always have to remember that individual barrels can vary a little on speed. I fire form 50g bullets at 3500 in my 23" barrel getting groups in the 2's and low 3's at the same time. Formed loads are at 3650 with the 50's and 3500 with the 55's in the 23" barrel. Add another 100 fps for the 26" barrel.
Fifty driver hit the nail on the head when it comes to headspacing an Ackley improved. Many gunsmiths are so concerned about the customer being able to fire the parent round that they headspace the AI the same as the parent round...big mistake. I will even take more than .004 crush on my AI's and bump the shoulder back on new brass to set the headspace for the new AI chamber.
One great advantage of having an AI is that you hardly ever trim an AI case. I have a flock of AI reamers and I have yet to ever trim a case...I'm sure it may happen sooner or later. I have never full length sized a 223 Ai case, but I am sure that it will happen on the IMI brass that I am shooting.
Of the 244 AI, 243 AI, 22/250 AI, the 223 AI is the only one of the bunch that is hard to get to feed from the magazine of my 700's. There was a fellow in Nv that I saw do a 223 AI that he got to feed by putting a very slight bevel on the back of the barrel to act as a "feed ramp". None of my barrels have this feature and it sure is a pain in the neck having to hand feed each and every cartridge.
I have played with a bunch of powders in the 223 AI with the 50 and 55g bullets. N-133 with the 50's seems to get the highest velocity with Benchrest accuracy and N-135 with the 55's is simply unreal shooting 3600 fps in my 26" barrel with formed cases. I shoot a lot of 2 3/4" clay pigeons at 400 yards and rarely miss unless the wind is really swirling.
I must caution everyone that has little experience with 133 and 135, it will vary as much as 1.0g in burning rate on the 223 case. Sometimes you seem to get a fast lot and then you get a slow lot, all within a 1.0g Variance, which is a lot for a small case like this.
I tried shooting the 133 in a 700V and 25.5g was a max load for a 50g bullet and the same load in my 23" Hart barrel, 26.3 was the accuracy load...go figure.