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1/11/2010 5:02:10 PM EDT
I recently did a Troy MRF-308 rail installation on a 20" AR. During the install, I just "eyeballed" the gas block (with the gas tube installed) when I aligned it up to the gas port on the barrel. Doing a simple test by blowing through the barrel shows there is airflow coming from the gas tube, but what is the best way to check for a 100% accurate alignment?

Thanks!
1/11/2010 5:42:24 PM EDT
[#1]
i took a straight edge and made an index line w/ soapstone from the barrel extension pin to the gas port. then i made a center line on the gas block.
i needed this gas block to be at top dead center as it is a YHM flip up front sight.
it was pretty easy.
1/12/2010 4:54:20 AM EDT
[#2]
Well the gas tube was straight and aligned, but I'm just wondering if the gas block is seated perfectly etc. It's flush against the shoulder. I suppose it should be fine. I'll range check it soon.
1/12/2010 6:58:57 AM EDT
[#3]
polymorpheous' way is a great way for TDC.  Depending on the block it may or may not be designed to use a hand gaurd end cap between the shoulder and the GB.  Putting it up against the shoulder will probably work in either case because the hole in the GB is usually over sized.  However, if you want to be sure to get the holes in the barrel and GB centered fore and aft, spin the GB upside down.  Center the set screw hole over the barrel port.  In that position you will see if it is up against the shoulder or offset the thickness of the hand guard cap. Mark it if you need to, spin the GB back in the right position and align the TDC mark along with the fore/aft distance.

This check only takes a second.  It takes longer to type how to do it than actually doing it.
1/12/2010 4:02:27 PM EDT
[#4]
And this works every time.  It's also a good check for short stroking , ejection problems
458
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