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Posted: 12/18/2005 4:14:00 PM EDT
[#1]
It's quite common for the gas-block to work it's way forward (toward the muzzle). Two reasons:
1) The gas-blocks that have the most tendancy to move are made of aluminum. The aluminum heats up quickly from the hot gases passing through it. It expands faster and more than the barrel and.......it's loose. I always heat the gas-block with a hot-air gun and tighten the set screws while the gas-block is hot and the barrel is cool. I have never had a problem after that. 2) the presure in the tube blowing the carrier rearward tends to force the gas-block forward. I have seen it many times where the gas-block moves just enough to cut enough gas flow to cause short-stroaking. Loc-tite does work. I flatten the set screws prior to assembly. I put a drop of loc-tite on the end of one of the set screws and install it. I use a digital protractor to align the gas-block and then tighten the set screw. I then put loc-tite on the second screw and tighten it. The loc-tite flows between the gas-block and the barrel and does keep it from sliding. When removing a gas-block that has been installed like this, it's tough to get it off. |
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Posted: 12/18/2005 4:29:12 PM EDT
[#2]
what about putting small divets into the barrel itself so the screws have a relief area?
By the way, who makes aluminum blocks...Larue, PRI..all steel... |
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Posted: 12/18/2005 4:36:13 PM EDT
[#3]
Yes, you can make "divots" in the barrel. DPMS has that done on their Wilson bull barrels. The block will not slide then but you still have to have the screws tight. I had an AR come in one time, the complaint was "It will shoot about 5-7 shots and then start to mis-fire" It turned out to be the screws on the gas-block. The weren't loose but they weren't tight enough. When the block heated up quickly it expanded and allowed enough gas to leak around the barrel to cause FTT.
DPMS, Olympic and many others are aluminum. I'm sure I haven't had them all in my shop, but by far more are aluminum than steel. |
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Posted: 12/18/2005 5:51:08 PM EDT
[#4]
Just got home from a 3 day 1k+ round class. Guy I went with had a PRI lo-pro gas block under a Samson rail. At the very, very end of the last day the gun stopped running. It was because the PRI gas block had moved forward. It had been loctited. Couple of the instructors had seggested using green loctite and staking the screws if he did not want to get it pinned to the gun. The loctite he used was not as strong as the green.
This is the first time I've seen it, but at least the second or thrid time ever heard of gas block secured with set screws doing this. Kind of makes me want to re loctite and stake the few guns I have with set screwed gas blocks. |
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Posted: 12/18/2005 6:09:07 PM EDT
[#5]
Note the little Red bottle. Thats all you need.
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Posted: 12/18/2005 7:20:12 PM EDT
[#6]
the question is if you stake it...how do you remove it?
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Posted: 12/18/2005 7:52:25 PM EDT
[#7]
This is why several experts that I listen to suggest pinning low profile gas blocks. I have not gotten it done to my LaRue's yet, but I plan on it.
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Posted: 12/18/2005 10:07:02 PM EDT
[#8]
Another product that I have been using lately instead of Loc-Tite is Rocksett. It is resistant to over 2000 degrees. Pinning is always better than set-screws
http://www.flexbar.com/NewPDFs/187-Rocksett%20CB400%20600.pdf |
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Posted: 12/19/2005 2:34:13 AM EDT
[#9]
While that seems to have been good most all of the time, aparently this has not been everyone's experience. |
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Posted: 12/19/2005 3:15:34 AM EDT
[#10]
The set screws will work if you also use red loctite the gas block to the barrel. To remove it after, just heat up the gas block and the loctite will melt. Barrel heat during normal firing does not get hot enough to melt the loctite.
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Posted: 12/19/2005 3:33:34 AM EDT
[#11]
You know of red loctite coming loose, and the gas block moving? |
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Posted: 12/19/2005 3:46:07 AM EDT
[#12]
Since I started using red loc-tite I have never had a problem.
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Posted: 12/19/2005 4:31:58 AM EDT
[#13]
dimples for set srews to sit in would help the sliding problem and i think red is the most you should use.
i had a bull bbl. that would do the same thing once in ahile so i dimpled the barrel where the set screws sat and red loctited them in. worked fine for me and the rifle have seen some use but nothing a actual tact class would do. green loctite is damn near permanent and will force you to destroy whatever you used it one if you ever have the need to remove it. trust me i know! green loctite is what alexander arms includes with their .50 beowulf brake and after installing it i needed to remove it cause i wanted to install a freefloat.. lets just say that if i ever purchase a freefloat for it it will be a samson/troy type freefloat 
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Posted: 12/20/2005 12:01:23 PM EDT
[#14]
how do you guys stake a set screw if its not flush with the gasblock.....and what do you use to stake steel on steel?
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Posted: 12/20/2005 3:28:03 PM EDT
[#15]
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Posted: 12/20/2005 4:04:56 PM EDT
[#16]
262 is good for 300 degrees max. Semi-Auto rapid fire will create temperatures easily exceeding 300 degrees which will liquefy 262. |
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Posted: 12/20/2005 5:23:47 PM EDT
[#17]
so whats the best way to do it?
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Posted: 12/20/2005 5:35:07 PM EDT
[#18]
We were doing a lot of shooting. My gas KAC block, which is secured with set screws and loctited held. Another guy I went with had a PRI gas block secured with loctited set screws, and his came loose. Loctite seems to be sufficient most of the time, this is the first time I have actually seen one shot loose, and have "heard of" 2 others.
They mentioned Noveske would drill in pin LaRue gas blocks to their barrels, and that pinning is the best. Short of that they said try green loctite which is good to much higher temps, and then to stake the screws. They even suggested applying loctite to the inside of the gas block (abviously staying clear of the gas port). After seeing what happened to my friends gas block, Im partial to trying that on a couple of mine. |
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Posted: 12/20/2005 5:37:38 PM EDT
[#19]
removed
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Posted: 12/20/2005 5:40:38 PM EDT
[#20]
first of all..how do you stake screws that are not flush with the block?
also....when one comes loose and moves..does the screws come undone or is the whole thing expanding so much that thewhole thing slides forward without the screws moving...if thats the case then staking the screws wont make a difference... if the screws are coming out, then sure stake em....what about the "divot idea" with red loctite and torque it down...if the screws dont move and the thing expands it wont move if the screws are in the divots.... Also...has anyones block made out of steel come loose? |
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Posted: 12/20/2005 5:52:58 PM EDT
[#21]
I don't use LocTite as a means of securing gas blocks so I can't say mine has. However, I have seen a few come loose. I suspect that heat cycles caused the screws to come loose after the LocTite melted away. If you need to stake the set screws and they are not flush then you should grind them down until they are. |
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Posted: 12/21/2005 1:33:29 PM EDT
[#22]
OK guys..heres what happened to me....I took apart one of my rifles...rebarreling with another.. anyway...I used blue locktite on a Larue....Brought home my propane torch and put it to it....
Screws came off...damn gas block wouldnt!!!!!!!!!!!. I had to end up putting it on a vise and hammer the damn thing off. (And I put this rifle together in the first place). It seems that the locktite and the some of the slight divots created by torqueing down the set screws held it together...I used a rubber mallet..wouldnt work...Had to bring out the steel hammer! So i think with the issue with set screws coming loose is definitely an issue with aluminum gas blocks and I cant forsee any possibility of a steel one with red loctite, if put together correctly, coming loose..... Thats why people like Steve at Adco and Mark at LT use loctite and say its sufficient....Noveske pinning em is over kill and makes it that much harder to service the rifle in the future... Its just my opinion....which could change, I guess if it ever comes loose on me. |
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Posted: 12/21/2005 2:03:12 PM EDT
[#23]
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Posted: 12/24/2005 3:26:20 AM EDT
[#24]
the PRI gas block flip up sites are clamped on....anyone know if they come loose with that design....I think my AR-10A4 is similar
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Posted: 12/26/2005 8:52:36 AM EDT
[#25]
do you guys know that there is 3 (i think) different types of RED loctite? they have different temp ratings and there is a new one by loctite that comes in a gel.. I got whatever liquid RED they had in stock but the gel is about $10...more volume and easier to control. the only reason I didnt get the gel because it may not flow to all the cracks...
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Posted: 12/26/2005 9:17:28 AM EDT
[#26]
Loctite is useless if the contact surfaces of the set screw threads and gas block are not thoroughly cleaned and degreased.
I use Acetone and a decreased in size Q-tip for the block. Try it and see how much gunk comes out of there. This is usually always the problem when Loctite comes loose. |
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Posted: 12/26/2005 10:42:47 AM EDT
[#27]
http://www.brianenos.com/forums/index.php?showtopic=16277
if you guys read up on Zak's tourny experience you will see some of the issues he had seen with blocks coming loose. Anyone know how hot a barrel can get under rapid fire conditions? If the barrel exceeds 300-400 degrees and the loctite melts, then it comes down to how the screws are holding.... Has anyone seen what melted loctite looks like after it melts? It turns white and I dont know if the physical capabilities are still there after it goes through a melting phase. I think placeing a dimple in the barrel and screwing it tight with loctite will be sufficient when using a steel gas tube.. I think staking the screw is a nice idea but makes retrievability difficult... Makes me want to put back my front sight block that came with the rifle. |
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Posted: 12/26/2005 1:12:23 PM EDT
[#28]
or just use a steel low profile block...
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Posted: 12/26/2005 2:51:25 PM EDT
[#29]
That may be true on a fastener but not so on a gas block or many other aplications. I use loctite to "bed" my barrel extensions into the receiver. I use Kroil to coat the inside of the receiver as a mould release. The loctite still does exactly what I want it to. I have used red loctite on the gas blocksw on over 700 uppers, have never cleaned the parts with any solvent and have NEVER had any of them come loose. |
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Posted: 12/26/2005 5:04:26 PM EDT
[#31]
I am far from the "mainstream" AR builder. My builds are all match-guns or long range varmint/predator rigs. My customers don't get them that hot so I don't have that problem. I have used the green loc-tite on some other applications and think it would probably be a better choice if you have the FA capability.
I know I have exeeded the heat limits of the red loc-tite and have never had any problems but I'm sure I never have the GB as hot as what you are talking. |
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Posted: 12/26/2005 5:27:03 PM EDT
[#32]
I have a Bushy Varminter and don't shoot much rapid fire, but went out one day and shot 2 30 rounders wih XM193 rickity-tick and then loaded up some CRAP BROWN BEAR ammo and shot half a mag before my gas block blew loose and I got no bolt movement whatsoever. Ended up shipping my rifle back to Bushmaster and they fixed it. Hope they re-staked or used loctite or whatever they use, cause I sure as hell don't want to have that problem again!
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Posted: 12/26/2005 5:50:08 PM EDT
[#33]
Your new barrel is avalible with a pinned on LaRue gas block. The gas block is installed with green loc-tite, the set screws are set into detents in the barrel and tightened with red loc-tite, then a taper pin is installed with green loc-tite with appx .040" barrel engagement. This does not deform the bore. Dont even think about taking it off. The green loc-tited gas block and red loc-tited screws in detents are more than enough. The pin is not necessary, but if you still want it, here it is. this is a quote from Noveske's.....you decide...the pics on the site dont have any staked screws http://www.jnrifleworks.com/cgi-bin/cart2/display.cgi?cat1=8 http://ken-co.com/permatex/threadlocker-green.pdf#search='green%20loctite%20290%20temperature' however...from what Ive been reading....green loctite really isnt has permanent as people think. it seems that loctite 272 is stronger and will take higher temps. http://loctite.com/int_henkel/loctite_us/binarydata/pdf/lt3770_Threadlockers.pdf look at the chart at the bottom. |
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