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2/2/2013 5:24:41 AM EDT
Any tricks of the trade when it comes to making sure the gas block is properly seated over the barrel gas port? Is there any forgiveness (degrees off center)?

PSA mid length, .750 barrel with a Troy .750 low profile gas block.
2/2/2013 6:38:53 AM EDT
[#1]
use a sharpie marker to index the gas block to the barrel. the hole in the gas block is larger than the gas port, so it will forgive a little.
2/2/2013 7:41:11 AM EDT
[#2]
you might have to account for the space the handguard retainer depending on how the barrel/gas port was built
2/2/2013 8:21:44 AM EDT
[#3]
I would be more concerned about a canted gas tube and it's fit to the gas key than mis-aligned gas ports.  As stated, the ports in the gas blocks are generous.
2/2/2013 8:41:42 AM EDT
[#4]
I use a ~6" piece of blue masking tape and line up the long edge with the center of the barrel and gas port. Like it was mentioned earlier the gas block hole is slightly larger than the gas port itself. You want to make sure the gas tube runs the center of the barrel so it isn't skewed when it's in the upper receiver. That could cause a problem with the gas key.
2/2/2013 8:50:11 AM EDT
[#5]
This
2/2/2013 9:22:34 AM EDT
[#6]
Thanks for the help guys.
2/2/2013 9:46:14 AM EDT
[#7]
Do you have and know how to use a set of calipers and feeler gauges?
Measure from the barrel shoulder to the center of the gas port.  
Measure from the back of the gas block to the center of the gas port.
Now the hard part.
Subtract.
Use feeler gauges to space the gas block off the shoulder.  I have seen them range from slam up against the shoulder to .050 off, so no particular measurement is written in stone.
Eye-ball it for TDC and you are done.  If you cannot eye-ball it close enough for TDC then get someone else to help you.
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