well do i??? basically need to let the gunsmith know soon....

Umm.. some details might be helpful. Barrel length for instance.

yeah that's true....sorry....10.5 barrel length, rock river upper reciever....

You shouldn't. Its probably going to be a carbine length tube. 6.8 run better with the mid length gas systems but on a 10.5" barrel it might be carb length. Call RRA they should be able to give you a definate answer.

Check would 68forums.com or the AR variants section of arfcom if you need any 6.8 Data. I have a KT68 first gen barrel and chamber at 18" I use for hunting. I also reload it