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5/7/2014 1:42:05 PM EDT
I have a precision rifle I am putting together and I seem to have gas related issues.  The rifle is not cycling all the way back to pick up the next round.  I have tried 3 different ammo version and it's only ejecting about a foot and half away from the port.  I have tried another lower from one of my carbines with similar results and a different bolt and carrier.  It's well lubed.  

I am using a Veltor low profile gas block on a 20" Kreiger barrel with a rifle tube.  On the back end I have a PRS stock with a rifle buffer, tube, and spring.  I took the gas block off and it was tight, the hole appeared lined up with the gas block hole.  The hole on the barrel will almost fit a 3/32 drill bit in.  The holes on the gas block and tube appear to be larger than the barrel gas hole.  The gas key on both bolts are fine.  

What else could cause it to short stroke?
5/7/2014 1:56:35 PM EDT
[#1]
Quoted:
I have a precision rifle I am putting together and I seem to have gas related issues.  The rifle is not cycling all the way back to pick up the next round.  I have tried 3 different ammo version and it's only ejecting about a foot and half away from the port.  I have tried another lower from one of my carbines with similar results and a different bolt and carrier.  It's well lubed.  

I am using a Veltor low profile gas block on a 20" Kreiger barrel with a rifle tube.  On the back end I have a PRS stock with a rifle buffer, tube, and spring.  I took the gas block off and it was tight, the hole appeared lined up with the gas block hole.  The hole on the barrel will almost fit a 3/32 drill bit in.  The holes on the gas block and tube appear to be larger than the barrel gas hole.  The gas key on both bolts are fine.  

What else could cause it to short stroke?
View Quote

Ammo type? If the gas port is ~3/32", it's certainly large enough IMO, at least compared to a carbine. Are there any burrs on the gas block? Also, might not be a bad idea to check the screws on the bolt carrier key. If for some reason too that the key's hole is blocked, that could cause some short stroke issues.
5/7/2014 1:57:21 PM EDT
[#2]
You don't have your gas block pushed against the barrel's shoulder, do you?
5/7/2014 2:02:06 PM EDT
[#3]
Quote History
Quoted:
You don't have your gas block pushed against the barrel's shoulder, do you?
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That was my first thought as well, gas block not being lined up.  
5/7/2014 2:06:37 PM EDT
[#4]
So is it actually failing or just not ejecting brass far enough?
5/7/2014 2:28:50 PM EDT
[#5]
It's failing but not consistently.  Sometimes I can get multiple rounds off.  Yes the block is against the shoulder.  Shouldn't it be?  It appeared to have a perfect carbon build up around the gas hole on the barrel which I thought would indicate the gas block hole and the hole on the barrel were lined up?
5/7/2014 2:32:36 PM EDT
[#6]
If I turn the gas block upside down and run it to the shoulder on the barrel the gas holes line up as the hole for the set screw is the same as the hole for the gas.
5/7/2014 2:47:18 PM EDT
[#7]

Quote History
Quoted:


It's failing but not consistently.  Sometimes I can get multiple rounds off.  Yes the block is against the shoulder.  Shouldn't it be?  It appeared to have a perfect carbon build up around the gas hole on the barrel which I thought would indicate the gas block hole and the hole on the barrel were lined up?
View Quote
On many barrels, the block is backed away from the shoulder by the thickness of the traditional end cap (~.040"-.050") which might be installed in front of the block.  It's how all of mine are up to this point...

 
5/7/2014 2:47:55 PM EDT
[#8]
Quote History
Quoted:
It's failing but not consistently.  Sometimes I can get multiple rounds off.  Yes the block is against the shoulder.  Shouldn't it be?  It appeared to have a perfect carbon build up around the gas hole on the barrel which I thought would indicate the gas block hole and the hole on the barrel were lined up?
View Quote


in my experience the gas port on the barrel and the hole on the gas block line up a hair in front of the shoulder, the gas block shouldn't be against the shoulder.

Again, just my experience. YMMV
5/7/2014 2:55:31 PM EDT
[#9]
I do notice now that before the shoulder is a deepened cut, about an 1/16" wide
5/7/2014 3:03:28 PM EDT
[#10]

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I do notice now that before the shoulder is a deepened cut, about an 1/16" wide
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Try lining your gb up at the front of that cut...

 
5/7/2014 3:11:34 PM EDT
[#11]
I don't know if that matters too much. Example on my M4A1 clone, my DD gas block is against the shoulder, and based on measurement, the entire gas port is open under the hole in the gas block, but YMMV.
5/7/2014 3:22:44 PM EDT
[#12]

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Quoted:


I don't know if that matters too much. Example on my M4A1 clone, my DD gas block is against the shoulder, and based on measurement, the entire gas port is open under the hole in the gas block, but YMMV.
View Quote
A lot depends on the barrel manufacturer and gas block purchased.  The Viltor on my 16" middy had to be backed off to line up...

 
5/7/2014 3:32:30 PM EDT
[#13]
Pics of the barrel at the gas port??? What bolt carrier and buffer system are you using?
5/7/2014 5:08:25 PM EDT
[#14]
Two of the four builds I've done required a gap between the gas block and the barrel shoulder for the ports to align. The gap approximated the thickness of the end plate of a handguard.    
5/7/2014 5:09:19 PM EDT
[#15]
I am using a rifle buffer.  I am using a semi bolt carrier.  I think you guys are right about not having it up against the shoulder.  I believe the grove is for the hang used cap and I am probably not right on top of the gas port.  I will try it in the morning.

5/7/2014 5:10:40 PM EDT
[#16]
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A lot depends on the barrel manufacturer and gas block purchased.  The Viltor on my 16" middy had to be backed off to line up...  
View Quote View All Quotes
View All Quotes
Quote History
Quoted:
Quoted:
I don't know if that matters too much. Example on my M4A1 clone, my DD gas block is against the shoulder, and based on measurement, the entire gas port is open under the hole in the gas block, but YMMV.
A lot depends on the barrel manufacturer and gas block purchased.  The Viltor on my 16" middy had to be backed off to line up...  

In my case, a Colt barrel and Daniel Defense gas block. Maybe tolerance stacking in my favor?
5/7/2014 5:15:43 PM EDT
[#17]

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In my case, a Colt barrel and Daniel Defense gas block. Maybe tolerance stacking in my favor?
View Quote View All Quotes
View All Quotes
Quote History
Quoted:



Quoted:


Quoted:

I don't know if that matters too much. Example on my M4A1 clone, my DD gas block is against the shoulder, and based on measurement, the entire gas port is open under the hole in the gas block, but YMMV.
A lot depends on the barrel manufacturer and gas block purchased.  The Viltor on my 16" middy had to be backed off to line up...  


In my case, a Colt barrel and Daniel Defense gas block. Maybe tolerance stacking in my favor?
Or gas hole size in the barrel?  There are many factors.  I usually try to approximate by measurement...

 
5/7/2014 5:27:13 PM EDT
[#18]
The carbon buildup around the barrel port should show exactly where your GB should go. DO YOU HAVE A PICTURE???
5/7/2014 5:39:26 PM EDT
[#19]
I wiped it down.  I have the gas block back on and ready to try again.
5/7/2014 9:04:16 PM EDT
[#20]
I got back out to the range this evening after moving the gas block past the grove.  Works flawlessly now.

Happy, happy, happy

Thx for the help
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