Home Forums Hunting & Shooting AR and Tactical Rifles 221 Fireball in an AR

My Dad just got a Colt 6940 EBR, so far it has both the worst trigger and loosest upper-lower fit I've ever seen. But it seems to shoot all right.
I presume it will shoot better after the aftermarket trigger shows up and I do the "Arrington Trick" to the rear pin area.
But the experience has gotten me thinking about AR's again and I was wondering if anyone here has put together an AR upper or complete gun for .221 Fireball.
If yes, what issues?
Based on my inability to fire "gopher loads" in 223 in my 24 inch rifle, I would presume that gas pressure for the bolt is going to be on the short side, meaning either moving the port in closer to the barrel or lightening the buffer and/or bolt carrier.
So, has anyone done a Fireball AR and how did you make it work?

I would contact Marty at "Teppo Jutsu". I'm not sure if he has done a fireball, but he does a lot of custom chamberings. he invented the .458 Socom and a few other wildcats, so knows about proper port pressure and port diameter/ location. another place that has a good reputation is "Tromix".

if you have quickload you can do the engineering yourself. IIRC you need 12K-15K psi at the gas port. run your powders and QL will tell you what you have for psi at any distance from the cartridge down the barrel. then once you know the powder is making the appropriate psi at the correct distance you open your gas port to get reliable function.

advntrjnky

It should work fine, since the 300 Whisper is the Fireball necked to 30 cal

What's the "Arrington Trick"??

Whore working in Arlington, VA

If you're going to go to a custom upper for a .221, why not get a custom .223 with an adjustable gas port to allow you to fire low pressure .223 loads?

No expensive brass to chase, no extra set of dies, and you can still run full patch .223 by adjusting the port.

I've shot the 35 v-max loaded over blue dot in a .223, crazy accurate and very mild report. I didn't have an adjustable gas port upper so it turned the gun into a straight pull bolt action

Im New to AR's and I am in the process of putting together one with a 1-14 twist for shooting 40G Vmax. Could you please elaborate on the adjustable port gas block. Is there any tuning that one could do to adjust at what point the bolt starts to move rearward.

Arrington Trick (what I call it, as I first heard about it in an article he wrote) is to place shims in the gap at the rear between lower and upper until the pins need a drift. Then you bed the upper pin boss into the lower with that stack of shims. Does what the Accu Wedge does, or those JP pins, just a bit more solid.
458 -- I got the same results you did with the 35s. Shot, at least for as well as that gun ever shot, but didn't cycle fully.
I love the Blue Dot load in my bolters, it's like having a hot-loaded Hornet that will actually shoot -- kind of like a Fireball, ya know.
I'll be taking a barrel off my AR, replacing it with a "retired" great shooter in short-throated 223 (I want to see what happens if you can load to fit and still fit in the magazine) and I was wondering what I might be able to get away with trying for the take-off barrel.

When i installed the JP on one of mine i would shoot and adjust until the bolt wouldn't cycle enough to pick up the next round and then back a halve a turn until it cycled every time you pulled the trigger. Sounds more complicated than it really was.