AR Sponsor
Posted: 9/4/2009 9:07:10 AM EDT
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Last night, I performed the simple task of installing a Krieger barrel into a SunDevil upper receiver, followed up a JP Rifles handguard, Evolution Gun Works gas block, and gas tube.
- I applied Loctite anti-seize to the barrel extension where it fits into the receiver, as well as to barrel nut threads. But, I did not apply any to the muzzle side of the barrel extension flange or the corresponding surface on the face of the barrel nut. Should I have? - How does one line up the gas tube hole in the barrel with the hole in the gas block? I assume the fore and aft positioning is determined by when it stops against the fatter part of the barrel between the gas block area and receiver. This gas block is a clamp on style and there is no indent for pinch screws to index to. The block can spin around the barrel freely. I thought about putting a hose over the other end of the gas tube and blowing through it to make sure the passage way to the barrel is clear. Should work? - The barrel extension is just a bit short of the cut out in the receiver. I think this is OK, but what I see is that the bottom part of the barrel extension is not dead flush with the edge on the bottom of the receiver. It is perhaps maybe a 1/2 millimeter edge. OK? One admission of an apparently stupid move and a question. I tried cleaning off some excessive anti-seize on the JP Rifles black steel barrel nut and it was resistant to removal with a toothbrush and Brake-Clean, so I used a brass brush. That brush pretty much left a brass color on the threads, which won't come off. I stopped after that, not sure if paint was coming off or brass was staying on, or...? I cleaned it well (brass color intact), applied anti-seize, and installed. I may be overly cautious...just trying to do everything right. - Phil |
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The main place to put anti-seize is on the threads.
If you want, measure the location of the gas port hole in the gas block, then do the same with the barrel. Preferably with calipers. A little lip there is fine, several of my ARs have a tiny gap there and they are reliable and accurate... Is the brass-ed part of the barrel nut exposed? Barrel nuts shouldn't be painted...probably just brass marks. If it is exposed, will it really matter to you? Oh wait... 
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On the gas port, I've successfully used a flashlight (bore light) to shine in the gas tube portion of the gas block, and then look in the barrel. When the light is brightest, you have it lined up! 
Tighten it up some so it doesn't spin easy, first. Also, lightly pencil a line down the barrel through the barrel gas hole, so the gas block is perfectly in line. |
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Quoted:
The main place to put anti-seize is on the threads. If you want, measure the location of the gas port hole in the gas block, then do the same with the barrel. Preferably with calipers. A little lip there is fine, several of my ARs have a tiny gap there and they are reliable and accurate... Is the brass-ed part of the barrel nut exposed? Barrel nuts shouldn't be painted...probably just brass marks. If it is exposed, will it really matter to you? Oh wait... The threads are good to go with anti-seize. At first, I coated all the threads and learned that all the threads would not be used, so decided to clean off, and that is when the brass brush came into play. Calipers could help, and thought of a good way to use these to best locate the block. I have dial calipers and will use those. I found siome pics of ARs and the lip I see on some is similar to mine. I welcome your experience with the same. The now brass end of the barrel nut is not exposed. I need to correct myself here. It was NOT painted, just gray/black, so not sure what was on it? If it was exposed, yes it would matter, but you already knew that... 
Thanks for your input. Phil |
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Quoted:
Last night, I performed the simple task of installing a Krieger barrel into a SunDevil upper receiver, followed up a JP Rifles handguard, Evolution Gun Works gas block, and gas tube. - I applied Loctite anti-seize to the barrel extension where it fits into the receiver, as well as to barrel nut threads. But, I did not apply any to the muzzle side of the barrel extension flange or the corresponding surface on the face of the barrel nut. Should I have? - How does one line up the gas tube hole in the barrel with the hole in the gas block? I assume the fore and aft positioning is determined by when it stops against the fatter part of the barrel between the gas block area and receiver. This gas block is a clamp on style and there is no indent for pinch screws to index to. The block can spin around the barrel freely. I thought about putting a hose over the other end of the gas tube and blowing through it to make sure the passage way to the barrel is clear. Should work? - The barrel extension is just a bit short of the cut out in the receiver. I think this is OK, but what I see is that the bottom part of the barrel extension is not dead flush with the edge on the bottom of the receiver. It is perhaps maybe a 1/2 millimeter edge. OK? One admission of an apparently stupid move and a question. I tried cleaning off some excessive anti-seize on the JP Rifles black steel barrel nut and it was resistant to removal with a toothbrush and Brake-Clean, so I used a brass brush. That brush pretty much left a brass color on the threads, which won't come off. I stopped after that, not sure if paint was coming off or brass was staying on, or...? I cleaned it well (brass color intact), applied anti-seize, and installed. I may be overly cautious...just trying to do everything right. - Phil You are over thinking this a bit. With respect to the fore-aft location of the gas block, if you are not using a hand guard cap (I assume you aren't) then you should leave a 0.025" gap between the gas block and the shoulder on barrel (I use an automotive feeler gauge from this). On aligning the gas block, you can pretty much eyeball it. If the gas block has a front sight, you can align it using a laser bore sighter, and looking through your iron sights. This is also a nice way to build a rifle where the rear windage adjustment comes out dead center. The the flushness of the barrel extension to the corresponding face in the upper receiver, I just looked at three of my rifles, one factory and two DYI, and they are all dead flush. I don't think a little mismatch will afect operation, but, you could look at this thread on lapping the upper receiver threaded barrel extension to close the gap a bit. Hope this helps... |
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Danner130,
Thanks for the reply. Was not aware of the .025" gap. No iron sights, scope only, or any sights on the gas block. The flushness you speak of I am familiar with and already checked with a Brownells tool. I didn't have to remove material as the face of the receiver (SunDevil) was perfect as is. What I was referring to is the edge of the barrel extension relative to the interior of the upper receiver bore for the barrel extension. You can see a small ridge on some photos of the chamber and extension when photographed through the ejection port. - Phil |
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If the barrel was not intended to be used with handguards, there may not be a gap...
Also, there is not exactly a "spec" for gas blocks, some put the hole in the "right" place, some have it in slightly different locations I fixed an upper for a guy at the range, the gas block needed to be moved .25" from the shoulder. |
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Phil, this may help. It's an easy way to check for a gap once you read through it. Good luck.
Gas block port holes, even normal FSB's are drilled from the bottom. On a set screw type, the front set screw hole is directly under the gas port hole (below, left picture). On a FSB, that hole can be seen under the sling swivel area (below, middle picture) If you put the gas block on in the right direction, spin it upside down, and align that hole over the barrel's gas port you will see if a gap is needed between the GB and barrel ledge. Using the top dead center mark on the barrel (described in an above post) and the distance from the ledge using the "upside down" mark, you have the two indicators that will almost always align the GB perfectly. I sacrificed an inexpensive YHM GB and use it upside down to mark and/or dimple the barrel for alignment. (below, right picture)   
ETA: The drill bits in the first two pics are for visual purposes only - they were not used for anything. In the last picture the drill bit is used for dimpling in the GB jig. |
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RLR350,
I see how that would work. I am at work and do not know if my gas block has a hole on the opposite side, but rather doubt it. The unit is here. http://egw-guns.com/store/index.php?main_page=product_info&cPath=53&products_id=170 I will have to look, but they may have simply slid a drill bit through the gap at the bottom of the block to drill the port hole. I'll check it when I get home. - Phil |
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I have not seen the bottom of that one, but when you get a chance to look at it you will probably see the hole split by the gap in the bottom. I have a DD clamp on and the split hole is there and I was able to use it for the mark/indicator. Just like on a regular FSB, it has no purpose except for where they drilled.
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