The reason I ask is I am trying to find away to get more out of my AR. I want to see if there is a way that a wildcat can be used in a standard AR upper. With as little mods as possable.

I wish I had bought an AR-10 to. Then I could of had a 243 and a 308 in the same rifle. With a bunch more choices in wildcats to chamber for it.

The 7mm TCU is a well established .223 wildcat. I used it for silhouette competition in a TC pistol with some success. Should make an interesting round in an AR.

Off the top of my head: .223 AI, .17-223, a couple of .19 and .20 caliber wildcats, 6x45, .300 Whisper, .25-223, and whatever else someone, somewhere may have cobbled together.

Basically any caliber 30 and under has been done, but I think to run through an AR, you would need to stick with the 25 caliber and under bores, as 6.5 and larger would make the OAL too much for the mag. If you want a larger bore, there are the whisper series, which use the 221 fireball case, a shortened 223, necked up to 6.5, 7mm and the most common 30 caliber.

If you aren't stuck on the .223 case, there are some thumpers in 45 and 50 caliber that run single stack in the mag, and have a radically rebated rim. I think they are called the 458 socom and 50 beowolf, but I could be mistaken.

The Ar15 can support the 22LR, 17Rem, 20 Tactical, 221 Fireball, 222 Rem/Mag, 22ppc, 6x45 (6-223), 6 ppc, 6.5ppc, 6.5 TCU, 7 TCU, 7.62x39, 9mm Luger, 40S&W, 10mm, 440 Corbon, 45acp, 458 SOCOM, 50 AE, and the JD Jones Whisper series. So there are actually quite a few choices for the ar15. Of course you could always get the 50BMG upper unit for your AR.