223 Ackley gains around 25 fps over the 223 when run at the same pressures.
Really, I don't have a pressure gauge but I've loaded and shot a few hundred thousand 223 and 223 AI combined. With a standard 223 24.7 gr of Re-15 (or Varget) and an 80 Sierra loaded long about all you get in the case and at that point brass life suffers on some barrels. With the same combo in a 223AI I can drop 26 gr of 15 (with less compression) and get great brass life. So I'm thinking with a 5% increase in powder charge I might expect a tad more than 25fps. I will stand by my 125 fps increase, because that is my experience . With 77's you are going to need to reduce AI charges a full grain to start. And as Rost states there is another aspect to the AI and I firmly believe it reduces bolt thrust in an AR. I also think it may decrease throat erosion.
As long as there is some positive headspace in an Ackley chamber firefoming is a non issue and good 223 shoots just as well as formed cases. I think mine were set up at maybe +0.001-2. Fired many 1000 rounds FF and never lost a case I can remember. Just make sure your gunsmith know WTF he is doing. I saw another shooter fire a 200-14x at 300RF while FF 223 in his Ackley. Chambering an AI and rechambering one are two different things.Had one AR Lilja,used, and my guy set it back a turn...one of the best barrels I've had... but rechambering is a lot of set up and a good reamer to get it right
If I were to build a new longish range AR for Varmints/deer it would be a 223AI. Krieger 1/7 22' varmint I would use 77 Scenars loaded to 2.30", LC or WCC brass and ACS (Stoner) 10 round mags loaded 6-7 down for function. If I was shooting gophers, for FF, I would load 60 gr Sierra or Hornady HP with any stiff 223 load be amazed again. 8208, H4895, or AA 2015 all work well. AS do 10's of others...as would any 52-55 gr bullet you might feed it. IMO, on an AR, the 22 Nosler and 224 valkyrie are a joke for someone that handloads given brass, bolt life, and barrel quality. I would not buy any [bleep] of the shelf were it me
