223AI With 90gr Bullets

[ThunderDownUnder]

The 90 grain Sierra MKs can reach an approx max of 2900fps in my long barrel 223R. I really like this caliber and have plenty of cases, etc and am about to build a 223AI.

I'll screw a 32", 7 twist Krieger barrel onto my Barnard action and see if I can make a 6mm BR competitor out of a 223AI shooting the high BC 90gr bullets. On paper it would appear that I should reach approx 2950fps with the 90 grainers and at that velocity if the accuracy follows then I could almost match it with the 6mm BR guns. I'm guessing the 80gr Amax bullets that I currently use in my 223R would easily reach 3000+fps in the 223AI. Its going to be interesting to see what pushing the 223 caliber to its safe limit will bring about.

I would shoot the 223AI over the shooter ranges (up to 500yds) in the F-Open class and my 6.5x47L at the longer ranges. Has anyone built up a 223AI with enough freebore to shoot the longer 90 grain bullets? If you have tried this combo out I would like to hear about how the combination of 223AI and 90 grain bullets performs.

 

[fivering]

A couple of years ago I built an AR with a 6.5 twist Krieger barrel in .223AI, with the idea of shooting the NM course with 77's loaded to mag length and single loading the 90's at the 600.
It works very well, with the following caveats:
With the 6.5 twist, which is recommended, the Sierra's regularly came apart above 2650 fps.
The JLK 90's, which are made with their 6mm jackets, have yet to fail me at above 2800.
I find that the 80 Bergers pushed at the higher velocities obtainable with the AI case shoot right with the 90's at the lesser velocity.
My best results came with H-4350 and RE-17 and Small Rifle Magnum primers.

 

[ThunderDownUnder]

Thanks fivering!
I really thought that the Sierra 90s coming apart at medium velocity was just a rare event but after reading your post I contacted Sierra. I contacted their Tech Support and got the following reply from Sierra's Duane Siercks...

"We developed the bullet for the 223 with a max velocity of around 2650 fps. We recommend not exceeding that velocity by much. Pointing might help, but we have not tested that as yet. Thanks"

It looks like I have escaped problems shooting them at 2800fps in my 8 twist barrel probably because I have been pointing them. This means a re-think is necessary and like you suggest maybe the 80 grainers shot at high velocity is a more reliable solution. I wont be buying anymore Sierra 90s as 2650fps is way too low to justify the cost of the 90s over Amax 80s which shoot superbly.

After giving this some thought and looking thru Berger's on-line catalog it seems their .224", 90gr VLD has a higher BC than any of the 6mm bullets they make. Looks like I will change over to the Bergers and see what velocity I can get in a 223AI chamber. If I can get my predicted 2950fps with the Berger 90s then the 6mm boys wont have much if any advantage over the humble 224AI.

 

[acloco]

Don't stop at the 223 AI. I just built a 222 Mag AI (204 ruger brass, necked up, and then fireformed)....using 80 gr AMax's at 3150.

 

[Longtrain]

My AI is a 1:8, 30” Hart. It pretty much shoots anything I feed it, from 52 SMK’s to 80.5 Berger’s. I had a good load with RE-15 and the 80.5’s, but with the shortage I’m saving my RE-15 for my Dasher. I stumbled upon some AA2495 at PV and picked up four pounds. I take the burn rate charts with a grain of salt, some showing it a little slower then TAC and some much faster then TAC.

So, I picked a low load and got a good seating depth at -.010. I worked up a load from low to a warm 223 Remington amount and then went beyond that in .2 grain increments. No heavy bolt lift at all, primers are ok, easy extraction, no case head marks.

My choice load groups at 100 yds are in the mid .2’s, SD is 3.25 and ES was 10. I’m going to test 20 rounds tomorrow and then see how they perform at a 100 meter prone match, then out to 300 and 600 yds.
Funny thing is that the powder charge and velocities are very close to what RE-15 gave me. My Magnetospeed shows me at 2989 fps. So maybe I stumbled on a good load with powder that I generally wouldn’t have thought of using, we’ll see how it rings out.

 

[Ned Ludd]

The two major considerations for pushing the .224" 90s are jacket failure and brass life. The Sierra 90 gr Matchkings have a very tough jacket, and have survived firing without issue at ~2850 fps from an F-TR rifle I have with a 6.8-twist 30" barrel that has caused jacket failures with both Berger 90 VLDs and Hornady 88 ELDMs. I suspect they will work well for your intended purpose. To be safe, I would still suggest going with a 0.219"/0.224" bore/groove configuration barrel. That approach has apparently solved the jacket failure issue for a number of shooters using other bullets and seems only prudent given your intended use.

However, the second issue of brass life may be another story entirely. Unless you're using double base powders, I'm curious what kind of brass you're using that can withstand the pressure necessary to drive the 90s at ~2900 fps from a 32" barrel? Loads running at ~2850 fps from a 30" barrel with 90s over H4895 are extremely hard on Lapua brass, with the expected life rarely exceeding 4 firings, and sometimes losing primer pockets after only one or two firings. If you can get away with using double base powders, the AI approach may work well. Otherwise, you're going to need some really stout .223 Rem brass to survive the pressure necessary to drive a 90 gr bullet at 2950 fps and get more than a few firings at most from the brass. Throating the rifle out from here to Alaska would certainly help lower the pressure necessary for a given velocity a little bit, but you're still asking a lot from the brass to generate that kind of velocity with a 90 gr bullet, and increasing the case volume with the Ackley Improvement won't improve the .223 Rem case head thickness or strength.

 

[xswanted]

Well since this thread is 12 years old hopefully they OP figured it out by now.

My 223ai is running the 85.5 Berger at 2850 from a 24” barrel.

88 ELDM runs at 2800

I would think 2950 with a 90 even from that long if barrel would be a stretch. Be interesting to see if the OP ever achieved it.

 

[Ned Ludd]

Good catch on the 12 year old thread. I missed that entirely LOL.