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Posted: 7/25/2010 2:59:21 PM EDT
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My nephew was looking to build an AR15 from parts, so I donated my Colt HBAR upper. He was told recently that the Colt HBAR upper will need modifications if he wants to mate it with any other manufacture since the HBAR is not Mil-Spec. Is this true? What modifications are needed if true?
Thanks in advance, Jim |
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I haven't messed with Colts in a long time, but it sounds like yours is a large pin upper and you're likely trying to mate it to a small pin lower. I do believe that there are "adapters" of a sort for doing this.
Unless I'm mistaken, the worst case would be that he'll need to get a new upper and swap all of the Colt parts to that upper. Not a big deal and worth doing to keep the quality Colt parts, although I'm not wild about HBARs. |
First off, welcome to arfcom. 
It sure sounds like a large pivot pin Colt upper [have one myself, an MT6601]. You may want to read this recent thread: link Do you have access to a caliper to measure the pivot pin hole ID? Does it have an integral carry handle, or forward bolt assist, or case deflector? A pic would be most helpful. Search will be your friend in the future, but cutting some slack is appropriate for well thought out first time post. 
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| Does your nephew have a 1/4" drill bit that's not buggered up on the shank end? If the shank end of the bit won't go or is a snug fit in the front pivot pin hole then the upper is milspec with a hole for a .250" pin. If the drill bit falls through and has about .060" clearance then the upper is old style Colt with the .315" pivot pin hole and is drilled on a different center than the milspec. Both of my HBARs have .250" front pins. |
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I used to have a pre-ban Colt HBAR A2 rifle with large oversized upper pivot pin hole but sold it near the end of the AWB because I wanted to have small standard receiver pivot pin.
The cheapest way is to get an adapter which adapts a large hole upper to a small hole pivot pin lower, be advised that a good number of brands would rotate while being opened and would not line up properly when closed. A better way is to either get a used or new upper receiver with small standard pivot hole, either with a fixed carry handle or a flat top rail, whatever your nephew prefers. I would recommend getting the flat top upper, if he likes the looks of the A2 carry handle he could just get a detachable carry handle for now, later on he could upgrade to optics. Here's a source for new CMT A3 flat top upper receivers with small size pivot pin holes, also you guys could look at the AR15.com Equipment Exchange section for new and used uppers, if you would like to get a new Colt brand upper receiver Brownells sells them. http://global-tactical.com/cmtuppercompleteinstock.aspx |
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