Colt Hbar large pin upper

redshooter

redshooter

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So I finally got my AR assembled. I've run into a few problems, but the rifle works pretty well so far.

The one that bothers me the most is my upper turned out to be a large pin, not small as the guy who I talked to on the phone at the time of purchase assured me it was. I talked to the shop and the Gunsmith sorted it out with an adaptor bushing that he sent right away. I was really tempted to send it back but its condition was pretty much like new and the price was right.

Does anyone have any experience with using a large pin upper on a small lower? I've put about 75 rounds through it so far and it's been flawless, but there's a slight gap at the back between the upper and lower near the buffer tube. I'm a little concerned that I'll get some premature wear. Should I be concerned? I'm tempted to just get another stripped upper receiver and transfer all the parts, but if it won't be a problem I won't bother. Any advise?
 
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Slight gap and minute amount of movement is normal for any rifle design with an upper and lower, you have nothing to worry about.
 
The bushing in the large pin upper is off set .
If the bushing rotates it will be out of alignment & the receiver & upper won't close properly .
You need to lock tight the bushing in the upper to prevent movement .
Make sure you get it in the correct position before the lock tight sets up.
I have built a few with the bushings & if you do it right you shouldn't have any problems .
 
#1bcshooter said:
The bushing in the large pin upper is off set .
If the bushing rotates it will be out of alignment & the receiver & upper won't close properly .
You need to lock tight the bushing in the upper to prevent movement .
Make sure you get it in the correct position before the lock tight sets up.
I have built a few with the bushings & if you do it right you shouldn't have any problems .
Click to expand...

How did you orient the bushing? I used some blue Loctite, but it moved slightly from where I placed it. The result is the fit is very good along the long flat surface, but it's larger than I'd expect at the back along the radiused surface at the buffer tube area. Regardless it functioned perfectly...unfortunately the only scope I have, I can officially say is pooched, POI changed about 8" straight up from one load to another. Funny, it grouped well, so I have a starting point once I get my paws on another lbs. of W748.
 
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I have a bushing that I use with my colt hbar upper on my small pin lowers. It can be a bit of a pain to get it matched up but once you do you're good to go. I would recommend keeping it on that lower but I hear some lock tight or a skim of jb weld can make for a more permanent solution to keeping it lined up.
 
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