Fire forming 223 Rem AI 40° in an AR-15 ..?
- Thread starter 'Freak
- Start date
Just finished setting up a new 223AI barrel for a bolt rifle. I simply turn the barrel down until it fits snugly against a piece of factory brass. Took it out yesterday and fired 15 Winchester 55gr factory rounds. Worked perfectly. You might have some feeding issues with a 40 degree shoulder in the AR.
I had an issue with a Rem700 that was re-barreled and chambered in 223AI. I had inconsistent results using factory ammo...with substantial (25%-50%) failure to fire with light strikes on factory ammo, including Hornady and Winchester. I brought the rifle back to gunsmith and we verified the chamber was to spec. We then began looking at the ammo. Surprise...the ammo was consistently short resulting in inadequate crush fit seal. The different ammo tested were as little as 0.005" short to as much as 0.015".
One solution is to have barrel set back (ie shorten the chamber) to account for non spec ammo. I decided to keep it as designed by PO Ackley, and then I found an acceptable ammo that match the chamber for fire forming. I also ordered some LC brass to fire form for the rifle.
One solution is to have barrel set back (ie shorten the chamber) to account for non spec ammo. I decided to keep it as designed by PO Ackley, and then I found an acceptable ammo that match the chamber for fire forming. I also ordered some LC brass to fire form for the rifle.
I used R10x (25gr) under a cheap 55gr bullet. The shoulders formed but were slightly rounded. It took a full load of Varget and a 77gr to finish them up and get the nice 40 degree shoulders with tight lines. Now I just start with 27gr of CFE223 and a 55gr pill. Then I start loading.
Expect a few dings on the shoulders. They'll buff out. I also use a rifle length gas tube and a standard carbine buffer with an adjustable gas block if that helps.
Don't let anyone tell you AR's won't shoot AI!
From the magazine, all in under one minute.
Gilbert,
That is correct. A .223AI chamber is set back so that when you insert a .223 cartridge the junction/intersection of the shoulder and neck create a tight fit (crush fit) when the bolt is closed. This seal keeps the gas from leaking back around from the case mouth and provides a front reference point/stop so that the body of case can expand correctly to fit your rifle's chamber.
Most modern 5.56 or .223 ammo is not being produced to spec. What I found from like 8-10 different varieties of .223 Rem factory ammo (tested bulk ammo through match target ammo) was that most were short (shoulder pushed back). My best guess is this is done to ensure bolt closure and feeding for any rifle's chamber, especially for AR15 platform. As a result I was either not getting any crush fit or only a partial seal. If shoulder was too short then there was no crush fit and when firing pin hit primer then the cartridge would get pushed further into the chamber but since there wasn't enough resistance the firing pin would not cause a detonation...just a light primer strike mark. If the case only formed a weak or partial crush fit then upon firing some of the gas would flow backwards around the neck/shoulder junction and retard the fire forming process. The end result looked like a case initially formed using the Cream of Wheat method (80% formed) with a rounded shoulder and would require a second firing to achieve full firing forming.
From some discussions it is common practice amongst gunsmith community to set back the barrel an extra twist or two to ensure fire-forming with new factory ammo. An alternate method is to upgrade the firing pin spring (Wolf replacement spring for Rem 700 is much better than cheap factory spring), and also check the length of your firing pin (some are a bit short. For me my rifle was already assembled so easiest fix was to swap spring and evaluate firing pin for potential replacement/upgrade. In my case swapping out the $10 spring was the easy answer.
As a result of this fiasco my gunsmith now swaps out factory firing springs in any Rem 700 he works on.
I’m getting ready to rechamber my 223 into 223AI. As you’ve found I’ve found lots of factory ammo that is short. The cheaper the ammo the more variance I’ve had.
jepp2
Gold $$ Contributor
Maybe my experience is kind of different. Although all my 223AI shooting is done in bolt actions. But I spend a lot of time firing AR's.
If the factory ammo is that short (and the shortest I have encountered was Fiocchi in 204R fired in an AR), I would consider using something else to fireform. If you take fired brass, you can set the shoulder where you want it.
Check your firing pin protrusion. Even with the very short Fiocchi, none failed to fire.
If your shoulders aren't forming sharply, increase you load until they do. I normally use near max loads in the parent cartridge to fireform with. And I don't shoot cheap bullets as the accuracy when forming will rival accuracy after formed. No use using up barrel life.
I would avoid creating a non-standard headspace to allow it to accommodate shorter factory loads. If you set it at the standard of -0.004" you should be fine.
Agreed. For instance I had an older box of Blackhill's ammo. It was a box of 50 and less than half fired even after multiple strikes. My firing pin was several thousandths shorter than what gunsmith typically expected. Luckily the spring swap was sufficient to get solid hit igniting the primer. The weaker factory spring just pushed the lose cartridge forward deeper into the chamber.
As soon as I realized my ammo issue, I purchased 2k of new surplus LC brass for fire forming. Reloaded half with SMK's and VMax, and the other half I played with Cream of Wheat method to rough form without burning up my barrel.
As soon as I realized my ammo issue, I purchased 2k of new surplus LC brass for fire forming. Reloaded half with SMK's and VMax, and the other half I played with Cream of Wheat method to rough form without burning up my barrel.
Oso,
I believe this is what happened with a new build of mine. The firing pin assembly has since been changed out with a new PTG Performance Assembly and awaiting a chance to be fired again with my new handloads. I did load them with new unfired Lapua brass with the bullet into the lands app. .015 Time will tell.
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My gunsmith and I were really frustrated until we figured it out. The PTG firing pin was going to be the next step if the replacement Wolf firing pin spring didn't do the job.
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