AR Sponsor
Posted: 1/19/2009 7:18:11 PM EDT
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Hi y'all, not new to shooting, but new to the AR. Have a 1977 Colt SP1 lower. Most ARs have a rear take down pin, but this one seems to have a screw instead. But it won't back out. It loosens when you turn it counterclockwise, then it tightens again. I looked on the schematics on the Brownells page and it shows that it is a reciever pivot pin, screw type. How on earth do I remove the thing? It seems to be some sort of retention screw, but I'm not up on the nomenclature. The reason why I want to remove it, is the upper is not a Colt and I'm getting an original SP1 upper to make it correct. Also, the schematic shows a screw on the port side (as opposed to starboard) and there is no screw in that side. It sure doesn't seem like I'm missing anything as the reciever halves fit together very well.
Another question: the hole where this screw is seems to be larger than those on other ARs. Does that mean that this upper will not fit another lower? |
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Just to make sure it is not the standard SP1 two headed screw right?
It sounds lika a standard tension screw but someone put it in the rear hole to tighten up a sloppy fit. I don't know too much about them but I would turn the screw until you feel that it is loose and then use a punch and only hand pressure to see if you can push it out. I don't know what way it would come out so I would try pushing on the solid side first and then the screw side. I would also try taking the stock off first to make sure the normal takedown detent and spring hole doesn't have anything inside it binding against the tension pin. EDIT: I bet the previous owner lost the detent and spring so the normal takedown pin wouldn't stay in. He probably didn't know to take the stock off to replace it so he just used a tension pin that holds itself in. |
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You got to be Navy , port , starboard . You should be able to hold one side while loosening the lock screw that holds the two pieces together. Once you get the screw out of the pin, you just push the pin out the other side . Yes , SP1s have what is called a "Large hole" upper . the lower has a larger hole than typical M16s and ar-15s . There are bushings and different configurations of pins/screws available that allow swapping the small hole and large hole parts . CDNN has some of these .
Just noticed that you said it was a tension pin. These are two piece , wedge shaped pins that may need to be tapped out to break the taper lock effect. Loosen the screw a few threads and then take a punch and tap in on the screw head. This should push the wedge out the other side. Should get it. |
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Quoted:
You got to be Navy , port , starboard . You should be able to hold one side while loosening the lock screw that holds the two pieces together. Once you get the screw out of the pin, you just push the pin out the other side . Yes , SP1s have what is called a "Large hole" upper . the lower has a larger hole than typical M16s and ar-15s . There are bushings and different configurations of pins/screws available that allow swapping the small hole and large hole parts . CDNN has some of these . I think he meant it is a tension pin in the rear hole. At first I misread and thought he was talking about the front screw too. |
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Quoted:
Quoted:
You got to be Navy , port , starboard . You should be able to hold one side while loosening the lock screw that holds the two pieces together. Once you get the screw out of the pin, you just push the pin out the other side . Yes , SP1s have what is called a "Large hole" upper . the lower has a larger hole than typical M16s and ar-15s . There are bushings and different configurations of pins/screws available that allow swapping the small hole and large hole parts . CDNN has some of these . I think he meant it is a tension pin in the rear hole. At first I misread and thought he was talking about the front screw too. This is what led me to beleive it is the front pin : "Another question: the hole where this screw is seems to be larger than those on other ARs. Does that mean that this upper will not fit another lower?" |
Sorry if I was unclear guys. Like I said, I'm new to ARs. Not navy, but I am a captain. 
Ok, I'm talking about the hinge pin, the one toward the front of the weapon that it hinges on after you take out the rear pin, which is the one above the grip. It does look like the item in the pic cbsaf just posted, but it does not have a hex cap on the port side. The starboard side has a flat screwdriver head. I'd post pics, but don't have a camera. We tried a punch already. No Go on that one, even tried to tap it, but didn't want to be too agressive. It does seem to have been installed to tighten up a sloppy fit. |
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Twist the screw head until it feels loose like you said it got right before it tightens back up. Open the rear pin so the gun is hinged. Tape aroung the hole to prevent scratches. Have one guy with a punch and hammer lightly tap the pin while the other guy hinges the upper back and forth.
Maybe that will work. It should come out. How many times have you turned the screw head counterclockwise? Maybe if you turned it enough it would seperate? |
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Quoted:
Nope. The upper has forward assist. That's why I want it off. I want to put the correct SP1 upper on it. Then that's why you're not going to tap it out. The upper is probably a small hole upper an the lower is a large hole lower. It is most likely the same pin that is in my second picture except the screw side isn't tapped all the way through. Then you're just going to have to do your best to unscrew it. If it won't then it may be cross threaded or rusted and may need to be drilled out. ETA: You may want to send it to an AR15 experienced gunsmith. If you do have to drill it out yourself make sure you use a bit that is a size smaller than a 1/4 and make certain you are right in the center of the large screw hole. Don't go deep enough to hit the takedown hole lug on the upper if you want to reuse the upper for anything because the small hole and the large hole aren't aligned on center. |
| I'll try again. Perhaps someone else will chime in with an idea. I'd sure hate to have to drill it out. That would be tricky. I sure do thank you for trying to help me. Sure makes me feel welcomed in this new place. I'll be offline until tomorrow evening. Gotta catch some shuteye. |
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