I'm looking at a barrel that has a 2" section for a gas block like a front sight block? Can I use a low profile 1" gas block on that barrel instead? My thinking is mill spec puts all the gas luck holes in the same spot anyway.

yes you can use a low pro gas block just be sure to make sure the gas port lines up correctly. some gas blocks are meant to go against the shoulder of the barrel and some are meant to have the hand guard end cap between the shoulder and the gas block . so you may or may not have to leave a small gap to line it up correctly

You are correct, Nanashi.  The longer gas block journal is for a military style front sight/gas block combo.  The typical lo-pro GB needs only the rear inch of that space.   Barrel makers will usually allow enough clearance on these longer journals for the military gas block to "sandwich" a sheet metal end cap at the rear to hold GI-type drop-in handguards.  These end caps are only about .020" thick, not enough to put a lo-pro gas block seriously out of alignment with the barrel port.  

To be sure your gas block is centered over the port, you should measure with your calipers the distance from the barrel port to the shoulder at the rear of the journal, then take the same measurement on your gas block.  If you feel its necessary, you can position a clamp-on gas block slightly forward of that shoulder.  If its a set-screw type, you are at the mercy of the barrel maker's positioning of the little dimple on the underside of the barrel.  Done right, that dimple will put your lo-pro in the correct position, but its always a good idea to measure first to confirm. The beauty of building your own rifle is that you know exactly how its fitted together.  good luck - CW

Awesome this will allow the gas block to be perfectly centered just in case the gas hole or hole in the block is slightly off.

Awesome just picked up the noveske no gas block 12.5" barrel next I'll send it to adco for shortening and all I need to finish the build is a gas block and gas tube. And my approved tax stamp.

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