In the market for my first Grendel.

[Sticks]

I looked at Primary Arms and they only list Radical Arms uppers, still within your price range. Concur with Sticks as to barrel length. A barrel of 24 inches is not needed to reach out to 1k.

For 1k, no, not needed. The extra est. 100FPS you would get over an 18" would be nice though.

If you were set on the 24", up your budget and go to the parent MFG - Alexander Arms - http://www.shopalexanderarms.com/Uppers-...eiver.html or
http://www.shopalexanderarms.com/Uppers-...plete.html