View Full Version : The barrel nut of Death!
This is my story about a very good friend of mine and I's experience trying to install a new BCM A3 receiver on an existing Bushmaster upper that I owned.
I purchased a Bushy M4 right after the ban expired in 04' from my local Academy store mostly out of celebration and at the time the price was right $799.97 and home it came with me. Now at the time I didn't care but it was an A2 so I purchased a Trijicon Reflex II for it and it installed with their "goose neck" mount and life was good. Well here we are today and I had several projects going on and wanted to convert it to A3 so I ordered one of Bravo Company's recievers and once again life was good. A few weeks after I had the parts together I took it to my buddy's house who has all of the necessary tools and fixtures to be our AR "doctor" and we set upon it. At first everything went smoothly disasembly went quickly but then disaster struck when both of his barrel wrench's would not loosen the nut!! We had to apply so much torque that the wrenchs were shearing the teeth off of the nut ahhhhhhh! O.K. plan B we then thought solder or thread sealant was the issue so out came the MAP gas torch and we heated the receiver and barrel up pretty good. Still no luck!! OK Plan C the Dremel came out and we spent an hour cutting the barrel nut off what the Hell!! After finally getting it off there was no thread sealant or anything we could figure that would cause this. Therefore our conclusion was that it was a P.O.S. non spec nut that Bushmaster installed. Well fear not we had a spare nut and the new reciever went together slicker than "greased Owl shit". Anyone else experience anything like this?
I am no expert by any means and have only put together a few AR's but it sounds like maybe the threads were gaulled (s/p)? Maybe BM didn't use grease to install the barrel nut and corrosion occured between the aluminum and steal which "welding/fused" them together. Anyways those are just my theories. Congrats on the newly updated AR.
Belmont31R
03-25-10, 12:38
Umm...heating the metal will cause it to expand making the parts harder to get off. Should have put it in the freezer which causes metal to contract, and should be easier to get off.
Heat can be used to break the bond if there is thread locker but its not going to make the barrel nut any easier to turn as the parts are going to fit more tightly together due to the expansion. When large pins are press fit into place sometimes the pin is actually cooled with liquid nitrogen or dry ice, and then put into place. As the pin warms it expands, and fits more tightly together than could be done with metals of the same temperature.
Look up the term "freeze fitting".
Umm...heating the metal will cause it to expand making the parts harder to get off. Should have put it in the freezer which causes metal to contract, and should be easier to get off.
Heat can be used to break the bond if there is thread locker but its not going to make the barrel nut any easier to turn as the parts are going to fit more tightly together due to the expansion. When large pins are press fit into place sometimes the pin is actually cooled with liquid nitrogen or dry ice, and then put into place. As the pin warms it expands, and fits more tightly together than could be done with metals of the same temperature.
Look up the term "freeze fitting".
I thought about that myself. I think that works but if both parts are the same temp then they both will contract or expand right? Obviously different steel reacts different ways but for the most part I always figured I would get one part really hot or really cold but if both parts were the same temp that the effect would be nullified. I am not a metal expert though. I have had problems getting gas blocks on and off and I figured Heating the gas block and cooling the barrel would make for a nice fit. I may be wrong though as I am not a metal expert by any means.
Rubiconmike26
03-25-10, 13:42
yeah we had an issue like this with a BCM Upper. we had to switch the barrel nut because my friend has Troy battle rails and they use a diffrent barrel nut. So long story short after about 3 hours of heat gun and breaker bar we got it. what a pain in the ass though. Just the way it goes sometimes.
I think they were heating it up to try and remove/destroy any thread locker (ie red loctite) or solder that may have been used during assembly, though apparently that wasn't the issue.
Belmont31R
03-25-10, 14:12
I thought about that myself. I think that works but if both parts are the same temp then they both will contract or expand right? Obviously different steel reacts different ways but for the most part I always figured I would get one part really hot or really cold but if both parts were the same temp that the effect would be nullified. I am not a metal expert though. I have had problems getting gas blocks on and off and I figured Heating the gas block and cooling the barrel would make for a nice fit. I may be wrong though as I am not a metal expert by any means.
Yes you can heat the part that something is being inserted into, and the inserted part is cooled. By heating both parts they are expanding. AL has about twice the thermal expansion coefficient as steel does, and the parts will be harder to separate. http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html
Here is a description of this: http://www.nitrofreeze.com/2009/06/shrink-fitting-tight-tolerance-parts.html
Cooling both parts will have the opposite effect since AL has a higher coefficient. The AL will contract more than the steel causing the bond to be weaker, and that makes getting that barrel nut off that much easier.
I had a very similar situation in Iraq with our Bushamsters that had YHM rails installed. From what I could tell they applied something to the barrel nuts and then torqued the living shit out of them. In the end I had to cut several of the rails, and nuts off.
I also tried using heat as well. No joy.
Thats just what I needed to read. Gonna take my barrel off tomorrow.
Yes you can heat the part that something is being inserted into, and the inserted part is cooled. By heating both parts they are expanding. AL has about twice the thermal expansion coefficient as steel does, and the parts will be harder to separate. http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html
Here is a description of this: http://www.nitrofreeze.com/2009/06/shrink-fitting-tight-tolerance-parts.html
Cooling both parts will have the opposite effect since AL has a higher coefficient. The AL will contract more than the steel causing the bond to be weaker, and that makes getting that barrel nut off that much easier.
It won't contract "more", it will contract "quicker".
The technique is to freeze the whole assembly then hit the external nut with heat fairly quickly without damaging things. You have about 15 seconds to hit it with heat and back it off before the heat is transfered through the threads and it correspondingly heats up also. You can usually get a few more degrees to work with by using dry ice. It's fairly readily obtainable, think I've seen it at meijers even. If it doesn't budge don't keep throwing heat at it, cool it all the way down and come at it again another time.
I just had the same issue with a Bushmaster 11.5. I didn't think I would ever get the nut off. I heated it, used a 100lb setting on the torque wrench, whacked it with a hammer. Finally after 2 hours it moved. There was no sealant or anything I could see. I put anti sieze on it before installing the new nut.
No anti sieze always makes it more difficult, always use it when assembling your uppers. Our agency also bought Bushmasters with Yankee Hill rails. The rails were very difficult to remove on the few I've had to disassemble.
I have found that rather than putting maximum torque at one time that throwing the Kroil to it and letting it sit for awhile, followed by the wrench and small, gradual taps with a hammer works better for difficult barrels.
There was absolutely no trace of any chemical residue on the threads. Yes we also used Kroil live and learn I just think it was a POS non spec barrel nut. Perhaps Bushy has some sort of hydraulic automated machine that installs the nut??
JeepDriver
03-26-10, 10:14
I had a YHM on a RRA 9mm that I spent 2 hours working in and killed 3 wrenches getting off.
Ended up needing a set or the vise grip chain pliers to break the barrel nut loose from the receiver.
No visible thread locker, the rail was a RRA factory install. Luckily we were taking it off to install a TROS 5.5" and a DD 7" rail so destroying the YHM wasn't an issue.
I had the exact opposite problem. BM but nothing on the threads of the gun I had. so they were badly galled and would not come apart.
Umm...heating the metal will cause it to expand making the parts harder to get off. Should have put it in the freezer which causes metal to contract, and should be easier to get off.
Look up the term "freeze fitting".
If you don't want to wait for the freezer trick to work, try spraying it with a can of dust remover turned upside down. That will flash freeze it quick. I've used that on rusted automotive bolts that you can't fit in the freezer.
Riley~~~
If you don't want to wait for the freezer trick to work, try spraying it with a can of dust remover turned upside down. That will flash freeze it quick. I've used that on rusted automotive bolts that you can't fit in the freezer.
Riley~~~
DO NOT do this!
The "flash-freezing" will asymmetrically cool the metal only where the stream of coolant hits it, causing the metal to be stressed where it contracts.
This may not matter for some parts, like bolts and nuts, that are either cheap or machined to looser tolerances. For something like a rifle barrel with much tighter tolerances, you can weaken the barrel, or in some extreme cases of over-zealous cooling, destroy it.
DO NOT do this!
The "flash-freezing" will asymmetrically cool the metal only where the stream of coolant hits it, causing the metal to be stressed where it contracts.
This may not matter for some parts, like bolts and nuts, that are either cheap or machined to looser tolerances. For something like a rifle barrel with much tighter tolerances, you can destroy the barrel.
Good call, I'm used to working on heavy diesel stuff. I forget that you gotta handle these rifles like they're new born kittens.
Riley~~~
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.