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Posted: 6/20/2013 1:07:03 AM EDT
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Now that the ordeal is over, I will post this story.
I ordered a Geissele Reaction Rod a while back so I could do my own upper work. I don't have any issues building lowers and suck, but uppers are fairly new to me. First order of business was a new barrel on my first PSA upper. The issue with it is that I was setting up two rifles to be identical, but I couldn't replace the A2 FH on the upper because it was pinned on a 14.7" barrel... I elected to just order a new barrel/gas block/gas tube/comp instead and keep the 14.7" as a backup barrel. Off to BCM's site I went, found the parts I needed and ordered them. They arrived soon, and I went down to my buddy's house (my mom doesn't have a vise... I'm on leave from Afghanistan and don't have a good shop setup) to work on it. The old barrel came off without issue with the help of the Reaction Rod. I greased the receiver threads, put the new BCM barrel on, attached a torque wrench to my armorer's tool, and started tightening. When I hit about 30-40lbs, I stopped and checked alignment. I needed to go a little further to align the holes for the gas tube, so I did so, being careful with my torque indications. I hit about 70lbs by the time the tube aligned. However, I felt like something was wrong, so I took off the torque wrench and started backing off the nut. To my surprise, it took just about all of my weight on the wrench to loosen...  And when it finally DID pop loose, it wasn't actually loose... the receiver was rotating on the barrel, with the nut locked firmly into place. I tried a few more times, but deciding to minimize the risk of further damage to the receiver, I used another friend's vise block instead of the Reaction Rod. The nut popped loose almost instantly and with little pressure.
Once it was disassembled, I saw that the barrel's index pin had sheared off completely, and the receiver had rotated almost 90 degrees  (like I said, I'm new to uppers).
I emailed BCM, told them the whole story, and they replied saying to send the barrel in to them. I did so. About a week later, I received what appeared to be a brand new barrel plus a good bit of swag from them (there's a reason I order a lot of crap from BCM!). This time, I decided to skip the torque wrench and instead just used some instructions I ran across here... snug and loosen 3 times, then line up the next gas tube hole. No problem, using the Reaction Rod. I also installed the new comp with no problem, and adjusted another comp on a different receiver with no issues. So... my question is... Has anyone else run across a similar problem using the Reaction Rod? I was NOT expecting that. I don't know if the torque wrench was calibrated correctly or not. I have a feeling I screwed up, but I'm eternally grateful to BCM for helping me out even in a questionable situation 
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However, I felt like something was wrong, so I took off the torque wrench and started backing off the nut. To my surprise, it took just about all of my weight on the wrench to loosen... And when it finally DID pop loose, it wasn't actually loose... the receiver was rotating on the barrel, with the nut locked firmly into place. I tried a few more times, but deciding to minimize the risk of further damage to the receiver, I used another friend's vise block instead of the Reaction Rod. The nut popped loose almost instantly and with little pressure.
When used properly, the reaction rod will allow you to put torque on a barrel nut without putting any stress on he index pin. That is the the whole point of it. I don't think the issue was with the reaction rod -- I thing you just got a bum barrel. Almost the exact same thing happened to me recently. |
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My take is the index pin gets loaded regardless of the support used. Are you familiar with the reaction rod? If so, how is the index pin loaded when one is used? I'm not arguing -- I"m just curious. Maybe I'll learn something new. When the nut is getting very tight, wouldn't it try to turn with, instead of on to, the receiver? Almost seems to me that the ideal set up would be to use two vices in tandem, one holding the receiver in a block, while the next behind it held a reaction rod properly inserted. That would stabilize all components except the nut, and remove stress on all other parts. Overkill though, and I doubt anyone ever has (or will) do it that way. Just not nec. in all but the rarest of cases I guess. And maybe it would hide a potential defect, like that which may have been uncovered this time? |
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It was bound to happen.
The Geissele Reaction Rod supports and braces the upper from putting pressure on the indexing pin in the same way that barrel blocks do... As in it doesn't. There are a lot of people I would like to say I told you so to, but they will just make up some lame excuse as to why this happened. 
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My take is the index pin gets loaded regardless of the support used. Are you familiar with the reaction rod? If so, how is the index pin loaded when one is used? I'm not arguing -- I"m just curious. Maybe I'll learn something new. Just the pictures and description. If you have one pull an index pin and try it without and let us know. |
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My take is the index pin gets loaded regardless of the support used. I agree with this. Any single fixture puts some load on the index pin. Two fixtures/vices would have to be used to keep the index pin unloaded. So to mitigate the torque load on the index pin, use the specified moly-fortified on the threads and torque shoulder. Try to stay in the lower half of the specified torque range. |
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My take is the index pin gets loaded regardless of the support used. I agree with this. Any single fixture puts some load on the index pin. Two fixtures/vices would have to be used to keep the index pin unloaded. So to mitigate the torque load on the index pin, use the specified moly-fortified on the threads and torque shoulder. Try to stay in the lower half of the specified torque range. I've assembled very many uppers professionally with the reaction rod and I haven't encountered nor can I think of a situation where you can put force on an index pin when using the reaction rod properly. |
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My take is the index pin gets loaded regardless of the support used. I agree with this. Any single fixture puts some load on the index pin. Two fixtures/vices would have to be used to keep the index pin unloaded. So to mitigate the torque load on the index pin, use the specified moly-fortified on the threads and torque shoulder. Try to stay in the lower half of the specified torque range. I've assembled very many uppers professionally with the reaction rod and I haven't encountered nor can I think of a situation where you can put force on an index pin when using the reaction rod properly. Sorry, but I respectfully disagree. You would have to hold the receiver as well (two fixtures). The mere act of torquing the barrel nut (with the RR or barrel blocks) will push the receiver into the index pin, since it is the stop. How severe depends on existing conditions and technique. The Reaction Rod or any single fixture can't keep the index pin from seeing some load. Not a huge deal, just keep the torque load reasonable. |
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So basically, if the index pin is mounted too far forward on the barrel (towards the muzzle end), the force of the barrel nut closing in towards the receiver can shear the index pin. When I first read this I thought the OP had sheared the index pin due to perpendicular (to the barrel length) forces applied while using the Reaction rod in tandem with tightening the barrel nut. I have a Reaction Rod and would think that would be impossible as the rod is locked into the barrel extension lugs. When you tighten the barrel nut, the only thing fighting you is the reaction Rod locked into the receiver extension lugs. Somebody care to correct me? I'm all ears. |
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So basically, if the index pin is mounted too far forward on the barrel (towards the muzzle end), the force of the barrel nut closing in towards the receiver can shear the index pin. When I first read this I thought the OP had sheared the index pin due to perpendicular (to the barrel length) forces applied while using the Reaction rod in tandem with tightening the barrel nut. I have a Reaction rod and would think that would be imposible as the rod is locked into the barrel extension lugs. When you tighten the barrel nut, the only thing fighting you is the reaction rod locked into the receiver extension lugs. Somebody care to correct me? I'm all ears. Well -- Direct-Drive has a point but it is exaggerated. The amount of rotational force on the index pin caused by torquing a barrel nut down is, I expect, negligible. Certainly not enough to shear off an index pin. In fact, typically the upper receiver would give before the index pin breaks. |
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Quoted: Quoted: So basically, if the index pin is mounted too far forward on the barrel (towards the muzzle end), the force of the barrel nut closing in towards the receiver can shear the index pin. When I first read this I thought the OP had sheared the index pin due to perpendicular (to the barrel length) forces applied while using the Reaction rod in tandem with tightening the barrel nut. I have a Reaction rod and would think that would be imposible as the rod is locked into the barrel extension lugs. When you tighten the barrel nut, the only thing fighting you is the reaction rod locked into the receiver extension lugs. Somebody care to correct me? I'm all ears. Well -- Direct-Drive has a point but it is exaggerated. The amount of rotational force on the index pin caused by torquing a barrel nut down is, I expect, negligible. Certainly not enough to shear off an index pin. In fact, typically the upper receiver would give before the index pin breaks. But the upper receiver (when using the Reaction Rod) is not in play. It is basically the white filling in an Oreo cookie getting squished together between the barrel extension and barrel nut (the cookie pieces)....At least the way I envision it. |
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If you have a reaction rod and don’t believe the index pin gets any loading, then install a barrel without the pin.
It seems like a simple enough experiment that does not require taking anybody else’s word for it. Personally I have seen a lot more posts about pins shearing than uppers giving. |
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So basically, if the index pin is mounted too far forward on the barrel (towards the muzzle end), the force of the barrel nut closing in towards the receiver can shear the index pin. When I first read this I thought the OP had sheared the index pin due to perpendicular (to the barrel length) forces applied while using the Reaction rod in tandem with tightening the barrel nut. I have a Reaction rod and would think that would be imposible as the rod is locked into the barrel extension lugs. When you tighten the barrel nut, the only thing fighting you is the reaction rod locked into the receiver extension lugs. Somebody care to correct me? I'm all ears. Well -- Direct-Drive has a point but it is exaggerated. The amount of rotational force on the index pin caused by torquing a barrel nut down is, I expect, negligible. Certainly not enough to shear off an index pin. In fact, typically the upper receiver would give before the index pin breaks. But the upper receiver (when using the Reaction Rod) is not in play. It is basically the white filling in an Oreo cookie getting squished together between the barrel extension and barrel nut (the cookie pieces)....At least the way I envision it. I'm not indicting the Reaction Rod. In fact, I think it's an excellent fixture....maybe the overall best of breed. It works essentially the same way as the USGI method (barrel blocks) and millions of rifles have been built that way. I think that the OP's issue came from either technique, a faulty index pin or a combination of the two. BTW, the receiver IS in play with the RR.....you are dragging it into the index pin as you torque the barrel nut. If your technique is good (moly-fortified grease, proper torque method) the pressure on the pin is minimal.....millions of successful builds stand in testimony. |
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Quoted: Thanks for the info! I learn something every day.Quoted: Quoted: Quoted: So basically, if the index pin is mounted too far forward on the barrel (towards the muzzle end), the force of the barrel nut closing in towards the receiver can shear the index pin. When I first read this I thought the OP had sheared the index pin due to perpendicular (to the barrel length) forces applied while using the Reaction rod in tandem with tightening the barrel nut. I have a Reaction rod and would think that would be imposible as the rod is locked into the barrel extension lugs. When you tighten the barrel nut, the only thing fighting you is the reaction rod locked into the receiver extension lugs. Somebody care to correct me? I'm all ears. Well -- Direct-Drive has a point but it is exaggerated. The amount of rotational force on the index pin caused by torquing a barrel nut down is, I expect, negligible. Certainly not enough to shear off an index pin. In fact, typically the upper receiver would give before the index pin breaks. But the upper receiver (when using the Reaction Rod) is not in play. It is basically the white filling in an Oreo cookie getting squished together between the barrel extension and barrel nut (the cookie pieces)....At least the way I envision it. I'm not indicting the Reaction Rod. In fact, I think it's an excellent fixture....maybe the overall best of breed. It works essentially the same way as the USGI method (barrel blocks) and millions of rifles have been built that way. I think that the OP's issue came from either technique, a faulty index pin or a combination of the two. BTW, the receiver IS in play with the RR.....you are dragging it into the index pin as you torque the barrel nut. If your technique is good (moly-fortified grease, proper torque method) the pressure on the pin is minimal.....millions of successful builds stand in testimony. |
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What the Geissele Reaction Rod should have been.
The design in the link above avoids the whole loading of the indexing pin issue via engaging the charging handle slot in the upper receiver, preventing the upper receiver from putting any rotational pressure on the indexing pin. |
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What the Geissele Reaction Rod should have been. The design in the link above avoids the whole loading of the indexing pin issue via engaging the charging handle slot in the upper receiver, preventing the upper receiver from putting any rotational pressure on the indexing pin. I used to work with a an ol' geezer and sometimes I'd ask, "Hey Don, how's that look ?" If he liked it, he'd say, "That looks so good, I think I just peed down my leg." That Reaction Rod Improved looks pretty freakin' good ! Don would have peed. |
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What the Geissele Reaction Rod should have been. The design in the link above avoids the whole loading of the indexing pin issue via engaging the charging handle slot in the upper receiver, preventing the upper receiver from putting any rotational pressure on the indexing pin. I used to work with a an ol' geezer and sometimes I'd ask, "Hey Don, how's that look ?" If he liked it, he'd say, "That looks so good, I think I just peed down my leg." That Reaction Rod Improved looks pretty freakin' good ! Don would have peed. 
I could see that, I wish they would just sell it. 
You can see it in use here starting at the 3:50 mark. |
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