Loctite?

abber

New member
Hey guys, I have another question about a possibly controversial and contested subject. I am honestly curious, and not trying to start any fights here. My question is about the use of Loctite. I am an industrial mechanic by trade, and have used loctite hundreds of times. I am new to the world of DIY AR rifles, however, and some of the stuff I see just doesn't add up in my mind.

First, I have always been told that Loctite is useless where extreme heat is present. I don't remember ever hearing what exactly these temperature extremes may be, but I am thinking that barrels and gas blocks would qualify.

So, as I ponder all the different things I have seen about building AR's (mostly on YouTube), I see things that don't add up. Some of the offerings are clearly sub par, and the guys posting them have no business trying to educate anybody, but others seem to know plenty, but still generate questions in my mind.

What are your feelings about using Loctite on gas block set screws? How about Loctite around the barrel extension, prior to sliding it into the upper receiver (the claim being improved accuracy)? Seems like silly speculation to me, but I could be wrong, hence this post.

On a side note, why use a set screw style gas block? I have only built one AR, but I opted for a pinch screw style low profile unit by Vltor. A little more expensive, but in my mind, mechanically superior, and won't damage the barrel or require dimpling.

The other thing that stands out, is the use of gobs of grease on the upper receiver threads where the barrel nut goes. I understand the difference in torque values for dry vs wet, but a thin film is all that is needed. When I assembled my barrel to the upper, I used a plumbers flux brush to apply a thin film of Slipstream grease, and torqued the nut on to the specified 50 ft lbs, and moved on (my barrel nut needed no gas tube alignment).

So anyway, that is all I have on my mind for the moment. Like I said, not trying to stir the pot, just checking myself. I have pretty good general mechanical knowledge, but most of you know a lot more about guns than I do, and I appreciate you reading all of this and providing any thoughts you may have on the subject.
 
LocTite will hold up to 425 degrees F, about the same temp where solder flows, so I think you are OK with it on a gun. If your AR ever gets close to that temperature, you will let go of it anyway.

And yes, too much grease does nothing to help torque values. THere is only so much clearance in threads.
 
Red Loctite requires 500 degrees to remove, and clearly some areas of a weapon- barrel and gas block/tube will exceed that temp. But I've never heard of them being used there.

The only place I use Loctite (blue) on weapons are scope mounts, scope rings, and action screws torqued to the proper values.
 
Sir;
If you fit things right you will not need loc-tite!
Harry B.

Im not a gunsmith, but I am a machinist and engineer. Listen to the words of Harry B..
I have often thought that you should need a license to buy Loctite. Believe it or not most people should be using grease or never seize where they are using loctite. To properly torque a screw you need lubrication. Properly torqued screws do not loosen. Consider loctite like a weld. If you wont weld that part dont loctite it. If you have vibration issues there are tacky products that dont harden which work much better than loctite. Also deformed thread screws, class 1 fit screws and nuts.
Dont believe me, check the machineries handbook.
 
Heavy recoiling handguns (Read, Ruger, three-screw, Blackhawk, Flat Top, .44 Magnum), before the invention of nylon lock-screws, were notorious for becoming loose from recoil. Green loctite would have been outstanding back then. I once sent in a Ruger Super Blackhawk as per Ruger request, to have a new cross-bolt retaining screw fitted and they replaced all the screw in the gun with new nylock screws.
Locktite has legitimate uses on guns, with consideration on what strength is required.
 
Dahermit's right and so is the boogieman (you didn't hear that kids).
Locktite used properly does exactly what it is designed for, not letting screws become loose from vibration, I use the blue locktite of every base and ring combination, and I swear by it, My scope are zeroed once and through the years they stay zeroed, no problems. Lubricating machine screws and proper torque also works for me unless there is pounding recoil, then I like to locktite them "properly".;)
 
If you have vibration issues there are tacky products that dont harden which work much better than loctite.
Uhhhh. Green Loctite? Green Loctite is a low-strength product that is intended for frequently removed screws. Blue would work well on scope mounts. Red is intended for permanent installations. Black Max...well, you get the idea.
As for correct torqued screws not requiring loctite, the screws on the Three-screw Ruger Blackhawk loosened no matter how tight I set them. Any tighter and I would have snapped them off. Perhaps that is why Ruger changed to Nylon lock screws?
Furthermore, how may gun owners have the proper torque wrench/screwdriver sitting on thier bench. How could the average gun owner apply the proper torque on the gun screws every time he cleans his guns?
 
640 Loctite is green, and it sure as hell ain't "low-strength!" It's a sleeve retainer and requires more heat than red (271) Loctite for removal.

I hate generalizations. Using red (271) Loctite on the threads of a Glock front sight is recommended by many sight manufacturers and keeps the sight from loosening up and getting lost. For those of you who buy into the "if you torque it right, you won't need Loctite" mantra, then you'll be happy to know that both Ameriglo and Brownells sell replacment front sights for Glocks. :cool:

I use a thin coat of grease on the receiver threads when torquing an AR barrel nut, the correct torque spec for which is from 36 lbs/ft to 80 lbs/ft. I usually torque to around 50 lbs/ft.

I don't use Loctite on scope rings; I use Torx head scope ring screws, and, per Leupold, use a tiny drop of oil before tightening up the screws.

When I was installing a Smith compensator on a "ban" AR barrel, I applied 640 Loctite, per instructions directly from Mr. Smith hisself. Have had to remove the brake a couple of times, and had to use a propane torch both times. I can't think of anywhere else I'd use Loctite on an AR, EXCEPT for the overtravel and engagement screws on my JP Enterprises triggers.
 
640 Loctite is green, and it sure as hell ain't "low-strength!" It's a sleeve retainer and requires more heat than red (271) Loctite for removal.
Whoops! You are correct. I looked it up and it requires heat. I do not know where I got the idea it was low strength. Anyway, Loctite states that Blue loctite can be removed with common hand tools. I only use blue on treaded fasteners.
 
There's also a green Loctite that's low-strength! I don't know what number it is. That 640 is tough stuff, though. I've done a bunch of rapid fire with my old Bushy, heating the barrel up, but that 640 has never released, unless I put a propane torch on it!
 
Boogieman said
Properly torqued screws do not loosen.

That certainly is an engineer's answer.

No disrespect intended, but as a 45 yr long mechanic, I'd say the world doesn't work that way. If it were the case, you'd never, ever see Nyloc fasteners, safety wired fasteners, 15 dozen different styles of lock washers, leventy seven different formulations of LocTite, etc.
Yes, every fastener has a proper torque. And having the fastener at that torque will pretty much guarantee that as long as the engineers did their job properly, you'll end up with the clamping force you were trying to achieve. But it is not now, and never has been, a guarantee that said fastener won't vibrate loose without something to prevent that from happening. It all depends on the materials used, and the application they are used in on a case basis.
 
I also tend to think that especially on the screws mounting the rail or ring bases to the action that the temperature extremes as the action heats up/cools can't help but want to loosen fasteners. Expansion/contraction of the metals would seem to be a ripe environment for that.

I see no disadvantage to Loctite...and one hell of a disadvantage to a scope coming loose in the field. So why not?
 
I own a couple hundred beater rifles and at the range I help other guys that cannot seem to sight in.

There are an infinite number of problems, but 50% of my problems and 50% of other shooter's problems have been loose scope mount screws.

Not scope ring screws, they almost never get loose.

In order to check mount screws, the scope must be removed, and what ever zero work had been done is lost.

I find that Loctite 242 on clean male and female threads makes for scope mount screws that never come loose.

Getting those female threads clean may not be easy. If the a barrel installed with grease, and the scope mount drill and tap in the receiver goes all the way through to the barrel threads, grease may want to ooze up through the mount hole.

Plan ahead, and use less grease. Clean the mount hole before screwing in the barrel.

For cylindrical bond, not thread locking, I use Loctite 601, as you can see in these pics of a VZ59 machine gun barrel I put on a Mosin Nagant. I made a sleeve from 1010 steel and bonded it to the outside of the barrel, so I would have a shoulder for the inner C ring of the receiver.
 

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  • VZ59 barrel reworked for Mosin Nagant 91 30 and sleeve   Loctite 601 for cylindrical shapes 7-4-.jpg
    VZ59 barrel reworked for Mosin Nagant 91 30 and sleeve Loctite 601 for cylindrical shapes 7-4-.jpg
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  • Polishing VZ59 barrel sleeve 7-14-2011.jpg
    Polishing VZ59 barrel sleeve 7-14-2011.jpg
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Properly torqued screws do not loosen.

Wrong.

It depends on vibration levels.

Even seen all the safety wires used on aircraft and other high vibration environments?

Even deforming fasteners have limits.
 
loctite

i am a machinist,and a gun smith , harry b is correct. i torque the screws on my guns and scopes i also lightly oil the screws before i torque them ,never had a problem.
 
"Even seen all the safety wires used on aircraft and other high vibration environments?"

Sure, and I wondered why they didn't use Loctite. :D
 
"Even seen all the safety wires used on aircraft and other high vibration environments?"

Sure, and I wondered why they didn't use Loctite.

There is plenty of Loctite on smaller fasteners that cannot be safety wired, along with deforming fasteners (both make and female) and self locking fasteners.

Many are actually single use.

Once torqued the fastener may not be used again without being replaced.
 
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