:confused: Broke my LMT - MRP Locking Bolt!!!

A

Adamg_55

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Toronto, Bantario
Hey guys, new to the AR game and i recently received an LMT MRP with a 10.5" barrel, and i love it! Because i love it so much i stripped it down tonight and gave it a complete cleaning, soaked everything in CLP and wiped it all off leaving a very cleaned and well lubed rifle. So i go to put the barrel locking bolts in and i use the torque wrench to tighten them up, and put the rifle away. I then find out i have the spare batteries for my eotech in my pocket so i go to store them in the UBR. When i grab the rifle out of the safe something falls out on the floor, and its the rear locking bolt!!!!! the bolt snapped where the threads are, so i have a couple questions:

How much torque can these bolts handle? My torque wrench wasnt set overly high, its hard to tell exactly where it is, but its around 140 inch pounds.

Is there anywhere i can get some of these and quick? i was hoping for a range trip this weekend and its a special order item from questar. 4-8 weeks

Does anyone have one they would sell me?

Am i a complete retard? has anyone ever done this? or even heard about it happening?

If i did overtighten it, have i done any damage to the rifle?

I am a noob and need help, very frustrated right now! :bangHead:

pics:

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Relax, I've been there brother... The reason I broke mine was because the supplied T/W was faulty and didn't "break". Anyway Questar mailed me some new ones out right away. No problem.

Don't worry about doing any damage, theres a reason these bolts shear so easy and that's to prevent damage. All I do for mine is basically snug them up by hand, the grooves in the barrel where these bolts sit is what locks the barrel in, not necessarily the torque on the bolts. You just over tightened them, no biggy.

Just keep an allen wrench with you at the range and check them every hundred rounds or so, if there snug tight, then your fine...

Don't sweat it, it's all part of the learning curve, it happens to the best of us...
 
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Adamg_55 said:
So I should cancel my order with questar? I ordered two in case I do this in the future, and it came out to around $50
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DO NOT Order these from just anywhere, As mentioned above these are a certain grade and specific to LMT. Wrong bolts used void any warranty.

This is what the guys over at LMT told me. NEA is wrong in this case.
 
I just checked LMT's site... 140in/lbs; were you using a "click-style" or "long-needle" torque-wrench? If cheap-needle style, I wouldn't trust it for any kind of serious work.
 
I'd recommend a decent quality torque wrench - give it the proper torque, not 'snugged up'. You shouldn't have to stop every 100 rounds or so to see if your bolt has loosened off ala Robarms stuff....
 
dont coat the bolt threads with oil as it wont torque right as you cant compress a hydraulic fluid. The bolts are probably over a grade 8 maybe a 12 or higher, look at the heads it might have the rating on them. I dont have mine here or i would look. If you know the grade rating you can buy the right type at decent bolt supply shop.

I have removed mine and retorqed them mulitple times. IN fact what is wearing out on mine are the heads are getting abit deformed from the torx key.
 
beltfed said:
I'd recommend a decent quality torque wrench - give it the proper torque, not 'snugged up'. You shouldn't have to stop every 100 rounds or so to see if your bolt has loosened off ala Robarms stuff....
Click to expand...

Actually, this is what one of the guys over at LMT told me, he said he snug's them up tight if he's without his torque wrench. It makes sense it's not rocket science it's two bolts that lock a barrel in place.

If I have my torque wrench in hand, sure I'll torque to spec. I'm just saying don't over think it and keep an allen wrench on hand for peace of mind. For the times you are at the range changing barrels a snug tight will suffice.

Again, It's not brain surgery. Any man worth their weight should be able to tell by feel when tight is tight enough.
 
USP said:
dont coat the bolt threads with oil as it wont torque right as you cant compress a hydraulic fluid. The bolts are probably over a grade 8 maybe a 12 or higher, look at the heads it might have the rating on them. I dont have mine here or i would look. If you know the grade rating you can buy the right type at decent bolt supply shop.

I have removed mine and retorqed them mulitple times. IN fact what is wearing out on mine are the heads are getting abit deformed from the torx key.
Click to expand...

Actually, I would recommend applying a small amount of lube to the threads.
Not enough to induce a hydrolock, but with out lube, the threads may bind and your torque wrench
Could give you a false reading.
 
CanadianAR said:
Actually, I would recommend applying a small amount of lube to the threads.
Not enough to induce a hydrolock, but with out lube, the threads may bind and your torque wrench
Could give you a false reading.
Click to expand...

Small amount of lubricant is not a bad idea BUT

Do NOT torque to same specs 140in - lbs IF you apply some thread lubricant as it will significantly reduce the amount that you can torque it to. Trust me on this one.
 
Every bolt torque specification is given with lubrication as a standard. There's a reason big name lube companies specialize in thread lubricants. Actual bolt tension values varry wildly when torqued with no lube. I can't think of one bolt that specifies to be torqued dry. Such scenerios may exist on a space shuttle or a DNA testing centrifuge. Or low importance that just need to stay in and not break, wich are unlikely to be anywhere near enough strain to fail.

Also there is nothing wrong with the old style torque
wrench, the only thing a click type has on old flex type is you can hear when it's reached the desired torque. The old style far is more accurate dollor for dollar to a clicker. The reason flex's are so cheap is because there's nothing a manufacturer can claim they've improved on over a competing manufacturer. You want accuracy with a clicker, get out your credit card.
 
50calshooter said:
DO NOT Order these from just anywhere, As mentioned above these are a certain grade and specific to LMT. Wrong bolts used void any warranty.

This is what the guys over at LMT told me. NEA is wrong in this case.
Click to expand...

Hold on... I have to stop laughing for a moment... ok... taking a deep breath.

1) LMT does NOT manufacture socket head cap screws. They don't even have a thread roller that I am aware of.

2) The bolt in question is either an 8.8 or 10.8 grade fastener. Nobody on this forum will be able to take advantage of the difference. Trust me.

3) Gauge the thread, bring the original with you and go to a specialty fastener store. Should cost about .50
 
Claven2 said:
Hold on... I have to stop laughing for a moment... ok... taking a deep breath.

1) LMT does NOT manufacture socket head cap screws. They don't even have a thread roller that I am aware of.

2) The bolt in question is either an 8.8 or 10.8 grade fastener. Nobody on this forum will be able to take advantage of the difference. Trust me.

3) Gauge the thread, bring the original with you and go to a specialty fastener store. Should cost about .50
Click to expand...

Hmm, ok but I'm guna take the word of LMT over your Internet intelligence, but thanks anyway.
 
50calshooter said:
Hmm, ok but I'm guna take the word of LMT over your Internet intelligence, but thanks anyway.
Click to expand...

It's up to you, but my internet advice is free, the same advice stamped by an Engineer will cost what? A few hundred?

Or go pay $50 for a bolt from LMT if that makes more sense to you - no skin off my back.
 
Claven2 said:
It's up to you, but my internet advice is free, the same advice stamped by an Engineer will cost what? A few hundred?

Or go pay $50 for a bolt from LMT if that makes more sense to you - no skin off my back.
Click to expand...

Fair enough, but I wouldn't want to risk blowing up my 1700 dollar upper, or my face for that matter.

BTW this is an honest question. There is significant heat in that area, do these bolts have to be special to handle that kind of heat?
 
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