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Czgunner

LR308 (low) handguard problems

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My dad wanted me to help him out and install a free float handguard.

We have an Aim Sports 13.5" handguard. Made in China, and not very nice.

Anyway, my dad didn't want to spend very much money, so I installed it.

I found out that when the barrel nut is torqued down, the bolt will not engage the barrel extension. With the OEM nut installed the bolt goes home no problem.

Anybody ever hear of something like this?

I sent an email to the vendor stating that I would like to exchange it. I don't know what I expected for the price, but this is pretty lame.

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1 hour ago, Czgunner said:

I found out that when the barrel nut is torqued down, the bolt will not engage the barrel extension. With the OEM nut installed the bolt goes home no problem.

Was the gas tube installed, when the nut was torqued down?  Did it twist the gas tube in the upper?  That'll stop the BCG from going into battery, for sure.  When the gas key hits the gas tube end, because the gas tube moved.  Check the gas tube, and see if it's centered in the upper.  Remove the bolt from the BCG, and see if the BCG will go all the way forward, with no bolt in it - the charging handle will still bring it back, don't worry about that.  Charging handle doesn't care if a bolt is in the BCG or not.

Pics...

Edited by 98Z5V

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I performed all of those checks before posting here. Thanks for the ideas.

Carrier slides over the gas tube no problem. It’s definitly the bolt that is hitting. Barrel nut was installed without the gas tube mounted. Barrel nut off (or factory nut installed) the bcg runs in no problem. I was thinking that the barrel is somehow misalligning when the nut is torqued, but it only does it with this AIM nut.

Its odd, after dozens of AR builds, I’ve never seen something like this.

Edited by Czgunner

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4 minutes ago, Czgunner said:

 I was thinking that the barrel is somehow misalligning when the nut is torqued, but it only does it with this AIM nut.

 

Upper receiver cut for the barrel index pin a tight fit, or sloppy?  If it's a tight fit, I can't imagine that barrel turning when you tighten that barrel nut...

 

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Possible that nut has a high spot on the surface that bears against the barrel extension collar. If it is only applying force to one spot maybe it could force the extension far enough off center-line to rub. With the other nut not having issues I would make a pretty close inspection on that AIM barrel nut.

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Okay, I took the whole thing down again and pulled the barrel. Then the index pin fell out. That's not good. I think we may need to contact DPMS. I'm pretty sure something with the extension is out of spec. I've never had a pin fall out before.

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8 hours ago, Czgunner said:

Okay, I took the whole thing down again and pulled the barrel. Then the index pin fell out. That's not good. I think we may need to contact DPMS. I'm pretty sure something with the extension is out of spec. I've never had a pin fall out before.

As long as the Barrels Extension Flange is seated against the Upper Receiver the same as the factory barrel nut , there shouldn't be an issue . The Indexing Pin is a light press fit , not welded or anything like that .  Is the Indexing Pin Hole in the Extension damaged  or the Slot in the Upper Receiver ? 

Did you remove the Gas Tube from there Gas Block ?  If so make sure the Gas Tube Pin is in properly , in the hole in the Gas Tube for it , if you missed it , the Gas Tube will be out too far & interfering with the BCG from seating all the way in & bottoming out in the Carrier Key .

Photo's  

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