The ultimate SP1 barrel tester. Works well with the Ciener .22 rimfire conversion kit too.
Years ago, someone chastised me for even considering putting a scope on the tube. He was dead wrong and it works very well. See the Rodman Laboratories rifle in Blake Ezell's "The Black Rifle". The tube is very rigid and the scope "looks" where the bbl. is pointing.
The tubular handguard was made back in the early days of AR-15 competition by Mark Chanlynn of Colorado. It is all steel and cost a small fortune in 1984 or so. He was the first person who really started the AR's in competition in the late '70s. My original competition rifle is now disassembled and various parts are used elsewhere. It was not a good "shooter" by my standards when I bought it - and needed to be dissembled and 'thought out'. This I did, and afterwards the rifle was a consistent 10-shot 100 yard 5/8" to 11/16" gun with 69 gr. Sierras. It shot fine at 600 yds, except when I ran into a batch of out-of-balance Sierras. Long story here. Anyhow, I was shooting 'donut' type groups. You get the picture. At a particular 600 yd. prone 'any sight' match, I couldn't buy an X or 10 for sixty some shots. Grrr.
The fastest twist bbl. that was available in '84 was a 1:10" twist from McMillan's successor. It's still the best bbl. that I own, and is on its third rechambering. Don't let anyone tell you that AR-15s can not be rechambered. They are full of suds. Mark Chanlynn tried to convince me to build a 6mm X .223. But I knew Sierra was coming out with the 69 gr. bullet and so I held out for the .223 chambering. I'm glad that I did.
John Unertl senior worked for a German optical firm in WW-I. He came to this country after the war and worked for Fecker scopes for a while, then started his own company. His son, John passed away few years ago. He used to set up shop at Camp Perry during the Nationals. As far as optics go, this old 32X is better than any modern Leupold that I own - and I've compared them side-by-side.