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Posted: 9/13/2014 11:06:58 AM EDT
When installing a low profile gas block on a new build should I leave a gap where the front handguard cap would be.  This is for a spikes tactical 11.5" barrel and gas block.  I read somewhere when changing out a standard front sight to a low profile you needed to leave the gap where the end cap set.

Mavo
Link Posted: 9/13/2014 12:06:04 PM EDT
[#1]
YES.
Link Posted: 9/13/2014 12:07:23 PM EDT
[#2]
Thanks, going to finish today.
Link Posted: 9/13/2014 1:35:02 PM EDT
[#3]
It's not always a yes.

Instead of assuming one way or the other, why not measure the distance of the gas port to the barrel shoulder, and likewise port to front of gas block?
Link Posted: 9/13/2014 1:48:45 PM EDT
[#4]
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Quoted:
It's not always a yes.

Instead of assuming one way or the other, why not measure the distance of the gas port to the barrel shoulder, and likewise port to front of gas block?
View Quote


Truth.
Link Posted: 9/13/2014 2:12:24 PM EDT
[#5]
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Quoted:


Truth.
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Quoted:
Quoted:
It's not always a yes.

Instead of assuming one way or the other, why not measure the distance of the gas port to the barrel shoulder, and likewise port to front of gas block?


Truth.

+1

I spaced the low pro MI .030" from the shoulder on my last build.  I removed the gas block to change out the handguard, and the soot build up around the gas port made it evident that the block was drilled for use without a handguard retaining cap.
Link Posted: 9/13/2014 4:27:29 PM EDT
[#6]
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Quoted:

+1

I spaced the low pro MI .030" from the shoulder on my last build.  I removed the gas block to change out the handguard, and the soot build up around the gas port made it evident that the block was drilled for use without a handguard retaining cap.
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Quoted:
Quoted:
Quoted:
It's not always a yes.

Instead of assuming one way or the other, why not measure the distance of the gas port to the barrel shoulder, and likewise port to front of gas block?


Truth.

+1

I spaced the low pro MI .030" from the shoulder on my last build.  I removed the gas block to change out the handguard, and the soot build up around the gas port made it evident that the block was drilled for use without a handguard retaining cap.



Several YHM models need to be pushed to the shoulder as well.
Link Posted: 9/13/2014 4:28:56 PM EDT
[#7]
Remove the set screw, rotate the block upside down and view the location of the port relative to the hole in the block.
Link Posted: 9/14/2014 4:09:47 PM EDT
[#8]
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Quoted:
Remove the set screw, rotate the block upside down and view the location of the port relative to the hole in the block.
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Here's your winning answer.
Link Posted: 9/17/2014 9:11:36 AM EDT
[#9]
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Quoted:
Remove the set screw, rotate the block upside down and view the location of the port relative to the hole in the block.
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Perfect answer, some gas blocks differ where they have the gas hole drilled on the gas block so flipping it over allows you to see exactly where it is.
Link Posted: 9/17/2014 11:32:04 AM EDT
[#10]
I always measure mine, then use the proper amount of shims against the shoulder of the barrel.
Personally I've never had one that sat against the shoulder.
As far as vertical alignment. I'll clamp down the upper to my surface plate. ( or any flat surface will do )
I then use a Solid toolmakers square, and gage blocks set that.
One can also clamp down the upper. Then use an adjustable parallel under half of the gas block, to get it straight.
Then just tighten down 1 set screw. Once that's done, it's to the drill press.
Link Posted: 9/17/2014 4:57:03 PM EDT
[#11]
My Armalite and my PSA came right against the shoulder. My WOA came uninstalled, but I butted it directly against the shoulder and have never had issue 1 after many thousands of rounds. My other lo-pros came installed with hand-guards or spacers. Anyone ever actually seen a malfunction caused by the millimeter gap between the shoulder and the gas block, one way or the other?
Link Posted: 9/17/2014 6:16:43 PM EDT
[#12]
.025"

The JP gas block is designed to replace a standard military front sight assembly. If you have installed a free floating

hand guard on a military spec barrel, there will be approximately a .025” gap between the back of the gas block and the
shoulder on the barrel. This gap is where the forward hand guard retainer would fit if you were using a military hand guard.
This gap is important because it assures proper gas port-to-gas block alignment.


http://www.jprifles.com/document_pdfs/JPGS5_521.pdf
Link Posted: 9/17/2014 10:16:27 PM EDT
[#13]
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Quoted:
.025"

The JP gas block is designed to replace a standard military front sight assembly. If you have installed a free floatinghand guard on a military spec barrel, there will be approximately a .025” gap between the back of the gas block and theshoulder on the barrel. This gap is where the forward hand guard retainer would fit if you were using a military hand guard.This gap is important because it assures proper gas port-to-gas block alignment.


http://www.jprifles.com/document_pdfs/JPGS5_521.pdf
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Assuming it is a JP gas block....

It may or may not be .25 inches depending on manufacturer.

Just measure everything to be safe. Plenty of youtube videos for instruction.
Link Posted: 9/18/2014 10:02:34 AM EDT
[#14]
I have a handguard cap that I cut the edges off. Using this as a shim will get you to the ideal distance from the gasblock shoulder on a barrel.

Just stick it in between the barrel and the gas block, secure the gas block and remove the handguard cap.
Link Posted: 9/18/2014 11:24:44 AM EDT
[#15]
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Quoted:
I have a handguard cap that I cut the edges off. Using this as a shim will get you to the ideal distance from the gasblock shoulder on a barrel.

Just stick it in between the barrel and the gas block, secure the gas block and remove the handguard cap.
View Quote



Even easier using a .025 feeler gauge
Link Posted: 9/18/2014 12:01:02 PM EDT
[#16]
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Quoted:



Even easier using a .025 feeler gauge
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Quoted:
Quoted:
I have a handguard cap that I cut the edges off. Using this as a shim will get you to the ideal distance from the gasblock shoulder on a barrel.

Just stick it in between the barrel and the gas block, secure the gas block and remove the handguard cap.



Even easier using a .025 feeler gauge


It's not when you don't have a feeler gauge.

Why buy one when I can make one from spare parts
Link Posted: 9/18/2014 12:11:30 PM EDT
[#17]
This question comes up again and again. The BRDE dimple jig removes any questions and eliminates measuring about where to accurately position a set screw gas block. It also is a jig for precise drilling of the dimples. It is worth the price of ownership, especially if you build a lot. It also works on barrels without a shoulder like the new BCM ELWs and it confirms that factory dimples are in the correct location. There is a video on the second link that shows a top barrel maker's product with the dimple in the wrong location.

A gas block can be mounted without it. The jig ensures accurate placement so I bought it, and use it.

Dimple Jig at BCM

BRDE Site
Link Posted: 9/18/2014 9:34:04 PM EDT
[#18]
gas hole on the gas block is larger than the gas hole on the barrel, so it is totally fine if it doesn't align them perfectly.
Link Posted: 9/18/2014 11:31:17 PM EDT
[#19]
I have installed Troy, BCM, and YHM gas blocks all the way to the shoulder on many rifles.  Not a single gas malfunction yet.  As mentioned the hole in the block is oversized.  I always plug the chamber and blow air into the muzzle to check and make sure the gas tube is receiving adequate flow.  You will probably be just fine backing it off too, given the tolerances it should not be much of an issue.  It never has been for me.  
Link Posted: 9/19/2014 8:34:48 AM EDT
[#20]
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Quoted:
I have installed Troy, BCM, and YHM gas blocks all the way to the shoulder on many rifles.  Not a single gas malfunction yet.  As mentioned the hole in the block is oversized.  I always plug the chamber and blow air into the muzzle to check and make sure the gas tube is receiving adequate flow.  You will probably be just fine backing it off too, given the tolerances it should not be much of an issue.  It never has been for me.  
View Quote



While that does make it apparent that you have air/gas flow it is still a WAG as a partially block port will still allow air through.  It's easy enough to get a hold of the manufacture and ask the question of whether theirs is designed to be against or off the step, if the info isn't provided with the block.
Link Posted: 9/19/2014 10:25:42 AM EDT
[#21]

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Quoted:
While that does make it apparent that you have air/gas flow it is still a WAG as a partially block port will still allow air through.  It's easy enough to get a hold of the manufacture and ask the question of whether theirs is designed to be against or off the step, if the info isn't provided with the block.
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Quoted:



Quoted:

I have installed Troy, BCM, and YHM gas blocks all the way to the shoulder on many rifles.  Not a single gas malfunction yet.  As mentioned the hole in the block is oversized.  I always plug the chamber and blow air into the muzzle to check and make sure the gas tube is receiving adequate flow.  You will probably be just fine backing it off too, given the tolerances it should not be much of an issue.  It never has been for me.  






While that does make it apparent that you have air/gas flow it is still a WAG as a partially block port will still allow air through.  It's easy enough to get a hold of the manufacture and ask the question of whether theirs is designed to be against or off the step, if the info isn't provided with the block.
Or you can just rotate the block and see where the set screw fits over the port.  Either way mine are all installed correctly and double checked using the method previously described.  And the above listed blocks all worked out for me.

 
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