Quote:
Originally Posted by srm109
I'm planning to change the gas block on my AR to a "low profile". It currently has a steel picatinny block, but I don't need it for anything. I'll swap that block to my 22LR upper and mount a folding sight on it.
How do I get the low profile block in the right position to align with the gas port on the barrel? I used a torpedo level on the rail-type block, but there's no way to put a level on the low profile. Any suggestions?
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The way I align gas blocs is to plug the bore with a plastic cap and put a plastic hose in the chamber. Then allow air to flow monitoring the air volume with an airflow gage. I just move the gas block around until it maximizes the airflow then clamp it. No measuring required.
There is another method using a 1/4" long dowel pin which is just smaller diamter than the hole in the gas block or the gas port in the barrel (which ever is smaller) For a 30 cal barrel put a 1/4" outside diameter piece of plastic tubing down the barrel past the gas port, then put the pin into the gas block though the gas port hole, then slide the gas block onto the barrel. when the gas port holes align the pin wll drop into the hole in the barrel, locking the gas port to the barrel. Feel that the pin isn't binding and clamp the gas block. Then pull out the 1/4" plastic tube and the pin will drop into the bore. That only works if the bore is larger diameter than the thickness of barrel wall and the clear distance of the hlole into the gas block, That method won't work on a bull barrel 17 Rem, but it's quite simple and accurate for big bore barels.
Method 3. Use a borescope and look out of the gas port from the inside. Don't use the internal illuminator, rather use a light shining into hole for the gas tube, with the gas tube removed. I suppose you could illuminate it though the gas port itself with a fiber optic cable attached to a bright light source (green laser?). I haven't tried this method, but I have inspected gas ports from the inside and think it would work.
I use the air method as I have the fittings and gauge made up on my bench and it works with all barrels. You can actually do a decent job just by blowing though the muzzle end of the barrel with the chamber plugged (fired brass) and just listen to the hiss of the air flowing though the gas tube. The hiss changes pitch slightly as the two holes align.
I''ve never attempted to align a gas block by measuring and using pencil or scribe marks. The entire point is to get the holes aligned. Getting the gas tube to pass though the barrel nut squarely is just a matter of tweaking the shape of the gas tube. I use a dowel pin which just passes though the receiver casting to align the barrel nut before attempting to put the gas tube though it.
It's possble to make a real mess if you try to torque the barrel nut with a gas tube passing though it. How do I know that.... sigh...
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