Re: .22 18" HB AR15 Upper
My own price no object .22AR project is an 18" SPR barrel and bolt(M-262 only) from Frank White at Compass Lake Engineering.
Frank does Match Service Rifles and .22 trainers of equal precision and price.
I got the SS Douglas. Base for the Douglas 20" service rifle barrels is about $300, plus $50 custom charge for the non standard length 18" barrel. Shoots 3/8" and clover leafs @50yd with SK Standard.
I found out AFTER I got the barrel that Frank did the 5.56 barrels for the real deal.
The bolt together with the connecting link is about $240 with 3 mag inserts. BDM makes high cap mags for this conversion system.
Figure $100 for an upper, plus whatever handguard , sights, muzzle device, etc. Or at least $750 plus sights total.
Ballistic Advantage offers a variety of uppers in the Atchisson system, using Spike's bolts; I suspect he can do an 18".
Model 1 Sales offers a 20" barrel in service rifle or fluted bull configuration.