223AI load help

[montana_native]

I figured this round is common enough to post here...

I've been working up loads for this gun. 223AI, 28" fluted bull, 1:8 twist. I've got the 55 gr V-maxes shooting great but I am having a tough time finding a load for 75 gr A-maxes. To get decent groups I have to slow it down to around 2950 fps using Varget. I thought I had a good load using Benchmark powder but when I tried to reproduce the groups they almost doubled in size (~0.300 to ~0.525") at 3050 fps. It seems to shoot the light bullets great, but the 75 A-maxes have been giving me fits.

Are there any "go-to" loads for this combo? It's throated long. I can seat to 2.440" before touching the lands.

Thanks.

[dcloco]

What twist is your barrel?

Some 1:9 will stabilize the 75's, some won't.

69's work great with H4895, CCI450's, and Win/Rem brass.

[montana_native]

1:8 twist.

I forgot to mention that I am getting strange (to me) pressure signs with this gun. Easy bolt lift, no exjector mark, no flattened primer but when the loads get hot, the case is hard to pull out of the chamber after the bolt is lifted. A hot load requires a little backward rap on the bolt with my hand to pull the case out...

[Blue Avenger]

the .223 ai tends to swell the case just above the web when the pressure is high. this causes a sticking to the chamber that reduces what is transmitted back to the bolt head. Many guys are running pressures a lot higher then they think with there over max loads, waiting to see it show on the case head. If you check some of your new cases against some of your fired cases you should not have more then .0200 growth on a proper dimension chamber.

[dcloco]

1:8 twist.

I forgot to mention that I am getting strange (to me) pressure signs with this gun. Easy bolt lift, no exjector mark, no flattened primer but when the loads get hot, the case is hard to pull out of the chamber after the bolt is lifted. A hot load requires a little backward rap on the bolt with my hand to pull the case out...

Can you post a picture of a fired case from a "hot load"?

Bet your chamber needs polished.