BudsGunShop.com - Barrel and gas system

George, it is not fully Mil-Spec (this has a commercial buffer tube) although you can change the barrel and gas system anyway. This rifle has a 16" Superlight contour barrel.

George - yes, indeed, you can change the barrel/gas system out to any MilSpec barrel. I have no idea what would be 'limited;' about it. Any caliber/length barrel that works with AR-15 uppers will work. Whatever length gas system the barrel has, will work. You might have to change buffers, possibly, depending on the barrel length and size of thee gas port in the new barrel. This is as 'mil spec' as things get, as far as the upper receiver goes.