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abber
June 2, 2012, 10:52 AM
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.

Scorch
June 2, 2012, 12:07 PM
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.

Harry Bonar
June 2, 2012, 12:31 PM
Sir;
If you fit things right you will not need loc-tite!
Harry B.

tobnpr
June 2, 2012, 02:43 PM
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.

BoogieMan
June 4, 2012, 07:12 AM
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.

dahermit
June 4, 2012, 07:19 AM
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.

hooligan1
June 4, 2012, 07:34 AM
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".;)

dahermit
June 5, 2012, 08:42 AM
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?

eldorendo
June 6, 2012, 06:39 PM
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.

dahermit
June 8, 2012, 12:43 PM
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.

eldorendo
June 8, 2012, 05:00 PM
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!

Fleet
June 8, 2012, 06:01 PM
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.

tobnpr
June 8, 2012, 06:50 PM
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?

4runnerman
June 9, 2012, 10:43 PM
I use Blue locktite on action screws only.

Clark
June 10, 2012, 10:49 AM
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.

brickeyee
June 10, 2012, 11:23 AM
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.

Clark
June 10, 2012, 06:56 PM
Or the vibration frequency.
At high frequency, screws act like they are not there.

fishhawk
June 18, 2012, 08:31 AM
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.

johnbt
June 18, 2012, 08:45 AM
"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

brickeyee
June 18, 2012, 08:53 AM
"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.

Clark
June 18, 2012, 04:59 PM
Over the last 30 years or so, I have had a lot of different mechanical engineers that I have helped. I am an electrical engineer, and we don't get super bright MEs in electronics, because there are no moving parts, but we get a lot of MEs and we deal with shock and vibration.

The big problems with vibration are falling apart and breaking apart.
At a couple of companies, I will dig this book out of the ME's book shelf and explain it to them:
http://www.amazon.com/Vibration-Analysis-Electronic-Equipment-Steinberg/dp/047137685X

There are lots of applications with high vibration that will not shake loose, and there are lots of applications that will.

When I take a Rem700 barrel off, and find all that goop that the Remington factory left there, I know my calculations say it could shake loose, and they must have had a problem, but darned if I have ever been able to get a Rem700 barrel to shake loose. Vaughn offers a design change to fix this in the Rem700:
http://www.amazon.com/Rifle-Accuracy-Facts-Harold-Vaughn/dp/1931220077

Guns have lots of screws and pins.
The only thing that I have seen again and again and again that came loose are the screws that attach the scope mount to the receiver.

An indicator is two holes touching on the target, followed by two holes touching way over there on the target.

I am not sure why those screws are coming loose.

I have calculated how much torque that scope mount screws should have.
I have tested the yield point of similar steel that is not part of the gun, and my calculations are right on for the various lubricants; 1) clean and dry, 2) oil or grease, and 3) wax.

Nathan
June 18, 2012, 08:05 PM
I like many others here am a mechanical engineer. My opinion is that loctite has many good applications in guns.

I generally use low strength. I use thread locker for threads and sleeve retainer type for dovetails, etc.

This said, be sure to prep your surfaces with some light sanding and cleaning with alcohol.

When you apply it, you still need to keep bolts in there elastic range and have parts which fit together.

Loctite's place in design is when design, mfg and use came close to design specs, but something just missed. Instead of redesigning, add some loctite. It is a good designer band aid.

MLeake
June 20, 2012, 07:12 AM
It also works well for aftermarket sights, which might not stand up so well to torquing.

HiBC
June 20, 2012, 10:27 AM
My take:I generally put something on threads so its not dry,unlubricated steel on steel.(unless the instructions say so)

These days,I usually put never-seize on barrel threads,but,accepting I will have created a monster if I want to take it apart,I have locktighted some barrels .I am careful with my thread forms and fit to minimal clearances on barrels I thread,etc.I generally true all faces,too.I torqiue a barrel tight enough it wont unscrew,but I do not get crazy about it.Many benchresters use minimal torque on their barrels.

My theory,I wanted to fill in all the clearance and make it a dead joint.Agreed,with fresh,precision threads its probably not necessary,but on a 80 or 100 year old milsurp set of threads,they won't be perfect.

I think that is why Rem loc-tites the bbls in.Its to take out any flex room in the joint...Its not about the barrel unscrewing.

On screws,no need to make more trouble than necessary,many screws don't need it,but on scope mounting,I'll put a touch of sleeve retainer between the base and the receiver as a bedding compound. There are few mechanical fits that are perfect.I use blue on the base screws.

Scope base screws are small for the job they do.They do not engage a lot of depth of thread length.There must be some thread clearance.You hang a big heavy scope on those screws and shock them with recoil,I think of loosening a fence post by working it back and forth.
That is also hard on the female threads in the receiver.So,for me,the loctite is not so much about the screw rotating to unscrew,it stabilizes the joint,removes wiggle room.

Oh,if I ever do need to pull one of those barrels back out,I'm thinking a soak in a pan of hot peanut oil should get it up to temp ,

To the original question,There are few applications for loc-tite on an AR.

Yes,there are marginally designed aftermarket parts,but as the OP pointed out,there are alternate parts with better designs.

BoogieMan
June 21, 2012, 09:37 AM
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.


Here is a guy doing it right. You cant properly torque a screw/bolt without lubrication. The torque stretches the screw and put proper tension on the head to keap it from slipping and thus loosening. Without lube your torque settings are incorrect because your torquing against the friction of the threads -vs- the stretch of the screw/bolt.
There are extreme cases for non hardening locktite. IE: the engineer designed the part incorrectly or there simply wasnt room for the proper type/size of screw/bolt. When most people are using loctite I use never seize. If i want to sell a new part I use loctite so the customer cant tale it apart.

brickeyee
June 21, 2012, 11:06 AM
The torque stretches the screw and put proper tension on the head to keap it from slipping and thus loosening.

And there are probably far more applications that cannot tolerate locking torque than ones that can.

There are also applications that using locking torque is simply inadequate for the environment.

pgdion
June 21, 2012, 12:21 PM
The only place I use Loctite (blue) on weapons are scope mounts, scope rings, and action screws torqued to the proper values.

And the rear sight elevation screw of the Beretta NEOS. :rolleyes:

scout338
July 26, 2012, 02:41 PM
For scope base screws I lubricate, torque to spec, loosen, torque to spec again, remove screws, degrease, blue Loctite and finally torque to spec. Best of both worlds.

a7mmnut
July 26, 2012, 04:14 PM
Threads don't lock that way, anyhow. There are many clearance variations between the male and female minor/major diameters of the fastener and the threaded hole. The thin leading taper edge of the male thread contacts only a portion of the insert thread wall. That leaves the head of the fastener and the spacer or cap washer holding most of the torque anyway. Then, here comes your Loctite...

:eek:

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