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Posted: 10/27/2009 12:08:16 PM EDT
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I bought a Colt upper some time ago (before Obama) that is a 20" HBAR A2. I'm not sure how old it is, but it has the A2 style flash hider and no bayonet lug. I put it on a DPMS lower because I got a good deal locally (again - before Obama). I had to use an offset bushing to get the large pin Colt Upper onto the lower. It works, but there is some slop between upper and lower by the forward pin that reminds me too much of the worn out M16A1s I was issued when I was in the Army back in the 1980s.
I am thinking about replacing the Colt upper, and while I am at it, switch to a flat top so I have batter optics mounting choices. I like the 20" HBAR, and am not planning on bayonetting anyone so I am thinking about just buying a DPMS Upper and moving the barrel, etc. to it. Is there anything I need to worry about? Would it make more sense to just sell my whole upper (it is in excellent shape and has not been used much) and buy a new one? If I go for the barrel swap how much should I expect to pay? (I don't think this is something I can do myself - is it?) Is there demand for a used Colt A2 uppers with large front pins out there? Thanks in advance for your thoughts. clang |
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Just note that you will need to use one of the extra tall front sight posts if you later switch to an A3 upper receiver. The "F" marked front sights are taller to make up for the extra height of the A3 with the sights added to them. Personally, I would sell your upper and buy a new one that is setup like you want but obvioulsy you can swap the upper and even the front sight base too. Good Luck! |
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I had the same problem. I bought a pre-ban 20" barrelled Colt HBAR large-hole upper and adapted it to a standard DPMS A2 lower receiver. Too much slop and the adapter bushing would often rotate when trying to hinge open the action, resulting in binding. At almost 10 lbs I also thought the rifle was just too damned heavy, although it was a tack driver.
I bought a Cav Arms Mk II lower when Brownell's put them on sale a couple of years ago. This is the one-piece unit with the buttstock integral with the lower receiver. To make a long story short, it completely solved all my problems. The slop is gone, the unit hinges open properly now, accuracy appears to be the same, and the lightweight of the Cav Arms lower brings the total weight down to about 8 lbs. True, the rifle is more muzzle-heavy than before, but overall it suits me much better. You do have to use a carbine spring & buffer with the Cav Arms unit but so far reliability has been 100%. I think most people here have a good opinion of Cav Arms' products. You might consider this route unless the Cav Arms lower is just too different to suit you. Worked for me. -Z |
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Sorry if I was unclear. No, the Cav Arms unit is not specifically made for big hole uppers. What I was trying to say is that the required offset adapter bushing bound up in my DPMS lower but worked fine in the Cav Arms lower. Also, I had a lot of slop with the HBAR upper on the DPMS lower but there was almost no slop when I put the HBAR upper on the Cav Arms lower. It was tight enough that I didn't think it needed an Accuwedge.
I think it's probably a cheaper fix as well. Brownell's still lists the Cav Arms unit at $150, less if you're tapped into dealer pricing, and that's in line with what many stripped lowers cost. As of today at least the ones in black are in stock. They are also made in O.D. green and tan but those colors are currently out of stock. Below is a link to Brownell's Cav Arms listing if you're interested. You'll have to paste it into your browser; I don't know how to make it hot: http://www.brownells.com/.aspx/pid=1517/Product/AR_15_CAV_15_RECEIVER -Z |
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Thanks for the clarification Zimms.
Still not sure what I will do. If I swap out the upper, is there a BUIS that would work with the A2 front sight/gas block? I've got a compact ACOG that would probalby be my primary sight, but I'd still like to have functional iron sights on the gun. |
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Quoted: Yes, but you need to use a taller then standard front sight postThanks for the clarification Zimms. Still not sure what I will do. If I swap out the upper, is there a BUIS that would work with the A2 front sight/gas block? I've got a compact ACOG that would probalby be my primary sight, but I'd still like to have functional iron sights on the gun. for example: http://www.midwestindustriesinc.com/index.cfm?fuseaction=category.display&category_id=183 http://www.midwayusa.com/viewproduct/?productnumber=810857 http://www.bushmaster.com/products.asp?cat=21 (A2 Front Sight Post for Flat-Top Colts) RRA make them too! The front sight will just be taller the the ears that are supposed to protect the front sight. Reference threads: http://www.ar15.com/forums/topic.html?b=3&f=18&t=460397 http://www.ar15.com/forums/topic.html?b=3&f=66&t=444953 http://www.ar15.com/forums/topic.html?b=3&f=18&t=450251 http://www.ar15.com/archive/topic.html?b=3&f=4&t=388056 |
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Quoted: Thanks Quarterbore - This is a big help. So the difference between the standard and F marked front sights is 0.030"??? That's like 1/32" Couldn' t they have just designed the flat top uppers to be 0.030" lower??? Colt has fucked up more things then they got right over the years including the various AR-15s with oversized pins, funky blocks, and other crazy stuff to make things interesting for us but in answer to your question... YES, Colt could have made the carry handle a little lower or changed the rear sight and this would not be an issue.... Just like when Armalite made the mid-length they could have moved that gas block a little more forward and the barrel forward the bayonet lug would have matched the 14.5 carbine and 20-inch rifle. BUT, both companies screwed up and we have to live with it as everybody copied these INOVATORS  |
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