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3/30/2010 9:24:08 AM EDT
This is my seventh or eighth time barreling an AR upper, but I have an issue with this one.

Lightly used RRA flat top upper and new Bushmaster barrel are being mated together. Spent way too much time attempting to align the gas tube with the barrel nut, nothing was working correctly. Look down and the barrel is cocked way off to the left.

Removed the barrel from the receiver and found that there's enough slop in the upper to allow the barrel to shift from left to right. So, I've got too much slop to the left, which is the direction I need to turn the barrel nut, which is making my barrel turn to the left.

Tried a rubber mallet to the front sight to align this mess but that didn't help the issue. Is there a way to correct the play in this upper receiver?
3/30/2010 9:51:08 AM EDT
[#1]
I've never had to shim an indexing pin, but if the barrel pin fits loose in the slot in the upper, I would think you could cut some narrow pieces of sheet metal (maybe a soda can?) and use them to shim the indexing pin in the upper receiver slot.
3/30/2010 10:01:54 AM EDT
[#2]
Quoted:
I've never had to shim an indexing pin, but if the barrel pin fits loose in the slot in the upper, I would think you could cut some narrow pieces of sheet metal (maybe a soda can?) and use them to shim the indexing pin in the upper receiver slot.


+1.  You can also peen the slot closed in the direction you need, but that's asking for trouble, IMHO.
3/30/2010 10:12:53 AM EDT
[#3]
Quoted:
Quoted:
I've never had to shim an indexing pin, but if the barrel pin fits loose in the slot in the upper, I would think you could cut some narrow pieces of sheet metal (maybe a soda can?) and use them to shim the indexing pin in the upper receiver slot.


+1.  You can also peen the slot closed in the direction you need, but that's asking for trouble, IMHO.


I was thinking of peening it, worst case is a FUBAR receiver. I'll look around for some shim material first, I don't do soda.
3/30/2010 11:39:36 AM EDT
[#4]
Done! Beer can shim and a light peen corrected the problem and it's nice and straight now.

Thanks guys!
3/30/2010 12:02:52 PM EDT
[#5]
Quoted:
Done! Beer can shim and a light peen corrected the problem and it's nice and straight now.

Thanks guys!



Gotta love "Bubba's School of Basement Engineering"!  

Done it myself... I prefer to call it "Creative Ingenuity"

3/30/2010 1:26:00 PM EDT
[#6]
Beer can shims are great. I had to use them to shim the brake rotors in my 72 vette to get the runout correct.
3/30/2010 3:13:07 PM EDT
[#7]
Use a set of barrel vise blocks to hold the barrel when tightening the barrel nut instead of a receiver "clamshell".  This will index your barrel in the opposite direction with respect to the upper receiver.  Think about it.  It works.
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