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Posted: 1/2/2016 11:22:40 AM EDT
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I just bought a complete upper in 300 Blackout which has a free float Handguard.
I intended to install the upper on my Colt SP1 lower. The problem is the SP1 uses a larger front pivot pin (infact it is a screw with off set shaft rather than a pin) and there is not enough room between the front post on the upper and the barrel nut for the upper to fit on this receiver. It looks like the upper will fit on my Bushmaster lower, but for NFA reasons I have not actually installed the upper on that lower (10" barrel on the new upper). Now my question. Is the larger front pivot pin unique to the SP1 or is this fairly common on upper end receivers? Are there barrel nuts that will allow the use of free float handguards on the SP1? If not is is possible to remove a little material from the barrel nut to allow for the SP1 Hinge pins? I am fairly new to the AR platform and would appreciate some advice on how to proceed. |
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As far as I know, it was just SP1s and early Sporters that used the larger front pin. Fulton Armory sells an adapter that allows you to install a milspec upper: http://www.fulton-armory.com/frontoffsetpinfcoltlarge-holelowerandsmall-holeupper.aspx
What free float rail do you have? I'm not sure what other free float will fit, but the free float rails that use the standard delta ring (DD Omega, etc.) would probably clear. Cutting a piece of the barrel nut wouldn't solve your problem because most free floats mount over the barrel nut, and besides that you would be compromising the strength of the nut. |
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Thanks Johnieblue, but I was using the wrong terms.
I currently have the adapter pin in the front and a milspec upper. what I was calling a offset screw is actually the adapter to install a small pin upper on the large pin lower receiver. My problem is the Delta ring on my new upper is too close to the Front hinge pin on the upper. As a result there is not room for my large pin lower to align holes between the upper and lower. I need to create more space between the upper front hinge pin and the Delta ring. I was mistakenly calling the barrel nut delta ring assembly the barrel nut in my prior post. So I was not talking about altering the barrel nut only the delta ring. It looks like I could remove a little of the delta ring to create clearance and not significantly weaken the delta ring, but I'm not sure about that. It would probably be better to find a delta ring that provides the correct clearance, but if this problem was unique to a few SP1 and early sporter models, then there may not be parts available. |
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Can you post a pic of the upper and lower to an image host like Photobucket? That'll make it easier to see what you're talking about.
A flat slip ring is what SP1 uppers used and might give you clearance if a delta ring won't: Brownell's Link I've never seen a free float rail like the DD Omega installed using one, but the internal dimensions are the same so they should probably work together. |
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