This is not for an AR but I wasn't sure where to post it. Anyway I am looking at a Rem 600 rifle that is chambered for 222. I want a 223. How difficult or expensive would this be to have done? Thanks for any help/info. I don't know anything about the 222 cartridge but it seems pretty close to 223.

Remington 600's have not been made in quite some time now, and are fairly popular for those collecting and wanting a good shooter in this model. I would leave the caliber as is, otherwise you will destroy any collector value in it. As a varmint cartridge the .222 is a fine cartridge, and is very accurate. Considering this rifle has a slower twist anyway you really do not gain that much by re-chambering to .223. .222 brass is still made and will be for time eternal and is not hard to come by. In short, leave it as is or sell it and find a rifle already chambered in .223. I garuntee that if you want to sell the 600, you will not have a problem.

223 is actually 224. You may have problem or safty issue if you do so.

Wrong.

The bore diameter of the .222 Remington cartridge is the *same* bore diameter (.224") of the .223 Remington. The cartridges are very similiar, but not quite the same. The .222 came out years before the .223 and is a VERY accurate cartridge itself.

I am with the other guy, keep it the way it is.

If you want a .223, sell the 600 and go buy a  700 in .223.  You might even make a little money out of the deal!