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How is it possible to shear an AR15 barrel extension pin?(Update) Login/Join 
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(Update) I mailed the barrel to Adco a week ago Monday and received it back today. That’s pretty quick by any standard. The barrel is now properly mated to the upper and ready for a range trip.

Many thanks to you all for the help. It is appreciated.

Badcopnodonut!!



I was switching handguards this morning and managed to do just this.

I was using a reaction rod in my vise like I always do. Torque was set at 40lbs and the gas tube hole was just short of being lined up with the upper. No big deal, I applied a little more force to line things up and SNICK. The upper and barrel now are turning together in unison.

I feared that the indexing pin had sheared thru the aluminum upper. It never crossed my mind that the pin had broken.

I got out my clamshell block, removed the barrel nut and low and behold I find the pin had sheared off smooth leaving the upper undamaged.

This is not my first rodeo when it comes to AR15 uppers but I never knew this was even possible.

Has anyone else seen this?

This message has been edited. Last edited by: badcopnodonut!!,


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Posts: 2874 | Location: sunflower state | Registered: January 31, 2008Reply With QuoteReport This Post
semi-reformed sailor
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More importantly, how are you gonna fix it?



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― Robert A. Heinlein, Starship Troopers

 
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Originally posted by MikeinNC:
More importantly, how are you gonna fix it?


I’ll send it off for repair. A web search finds guys talking about drilling it out and replacing the pin themselves. JP Enterprises sells
replacement pins. I don’t have a drill press and would likely ruin an otherwise salvageable barrel.


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Posts: 2874 | Location: sunflower state | Registered: January 31, 2008Reply With QuoteReport This Post
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I've seen it happen before.

The only explanation I can think of is that the index pin is specifically soft so that it doesn't destroy the upper. It's only supposed to index, the barrel/barrel extension, but it is the "sacrificial" part, like how the gas rings in on the bolt are specifically supposed to be softer than the inside of the bolt carrier.
 
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Thanks for the input LDD. Would a little grease between the barrel nut and the mating surface of the insert ease the rotational forces and keep this from occuring again?


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Yes. Always use grease on the upper receiver threads. If not using grease, the force is higher than what you're seeing on the torque bar. At least that's what I've read. The Reaction Rod can exert a lot of force. I like the Reaction Rod. But to be safe, I prefer the Supper Reaction Rod with locks into the upper receiver unlike the regular Reaction Rod.

I sheared the index pin on one of my ARs when I fired a round that had a high primer. Adco can fix it for $40.

https://adcofirearms.com/shop/...broken-ar-index-pin/
 
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Ed308, thanks for the link to ADCO. I’ve always used anti seize on the receiver threads but never thought about the barrel nut/receiver area.


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quote:
Originally posted by badcopnodonut!!:
Thanks for the input LDD. Would a little grease between the barrel nut and the mating surface of the insert ease the rotational forces and keep this from occuring again?


Yes, it would. We always used a bit of anti-seize grease around the barrel extension before mating it with the upper receiver (not dry lube: graphite + aluminum = bad things).

There's no guarantee you won't shear another pin, but it's the most insurance you'll get during this kind of operation.
 
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As noted, this is an issue with the basic reaction rod. It locks into the barrel extension, but it leaves the upper free to be pulled/stressed by the barrel nut, and the index pin is bearing all of that stress.

Wish I knew this before buying one Roll Eyes . I'm likely going to keep using mine until I have an issue because money went elsewhere for the time being. The Midwest Industries one has a feature to interface with the charging handle slot to spread that stress out, isn't nearly as expensive as the Geissele Pro.
 
Posts: 5762 | Location: Romeo, MI | Registered: January 03, 2009Reply With QuoteReport This Post
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You should always use oil on the threads before torqueing them. Most torque specs are based on the threads being lubricated with 30 wt. oil (you don't need a lot of it on the threads), unless the torque specs specifically state use of another lubricant (moly lube, or lithium grease for example) or dry. Different oils will give the nut different torque specs than others, and you torque bolts based on stretch and not to snap them off.
 
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No love for the Magpul BEV block around here? I’ve been using one of those for years without issue. Keeps the upper from rotating and pins on so the teeth can’t work their way out of the extension on you.



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quote:
Originally posted by SigM4:
No love for the Magpul BEV block around here?


I like the Magpul BEV block myself.


....Shredding lead both barrels
 
Posts: 1952 | Registered: March 15, 2004Reply With QuoteReport This Post
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You should always use oil on the threads before torqueing them

While its better than nothing, no you shouldn't use oil on an AR for this use. The specified product for this is moly disulfide grease. Easy to get the specified product and a lifetime supply is $20.
That and in my TM the specified initial torque is 30 ft-lb. But I doubt the lack of lube was the basic issue nor the initial over torquing.
I use the geissle super to help on this, but I don't think its foolproof. The fact that ADCO has a stock item in their list of services suggests to me it happens with some frequency. But in any case you should properly lube before starting a barrel nut install IMO...


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quote:
Originally posted by Jelly:
quote:
Originally posted by SigM4:
No love for the Magpul BEV block around here?


I like the Magpul BEV block myself.


I've build several rifles with the BEV Block.

Unless it's a SUPER expensive barrel. Instead of sending it off. Why not just grab a Faxon barrel for $150 and be done with it?




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Remember - Training is not sparring. Sparring is not fighting. Fighting is not combat.
 
Posts: 7938 | Location: Alpharetta, GA | Registered: August 04, 2005Reply With QuoteReport This Post
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I wouldn't understand the recommendation of not fixing it for $40 via ADCO when a decent new barrel is way more than that....


“So in war, the way is to avoid what is strong, and strike at what is weak.”
 
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quote:
Originally posted by myrottiety:
quote:
Originally posted by Jelly:
quote:
Originally posted by SigM4:
No love for the Magpul BEV block around here?


I like the Magpul BEV block myself.


I've build several rifles with the BEV Block.

Unless it's a SUPER expensive barrel. Instead of sending it off. Why not just grab a Faxon barrel for $150 and be done with it?


It well worth the $40 to repair.


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Posts: 2874 | Location: sunflower state | Registered: January 31, 2008Reply With QuoteReport This Post
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Update at top of the page.


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ADCO are good people


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