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Posted: 1/10/2012 6:42:34 PM EDT
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I'm gradually accumulating the parts to put together an AR rifle. While going through my parts stash today,I found a number of SP-1 stuff,including the AR-15 bolt carrier out of my Colt SP-1 which now has a Colt M-16 carrier. My question is this: will this carrier work with the newer flattop uppers and where can I find a new bolt assy to fit it? I "think" I know the answers but want to make sure I'm not screwing up.
Thanks, Clint |
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I had not known of any external diameter differences from different types of Colt carriers, and I had used all of them from the SP1, C half moon type, and M16 auto, so it should work on any type of AR uppers.
If you want to have a Colt bolt assy, Colt directly sells them from their site (but they seem to be out of stock at the moment), also check out the EE and other sites like Gunbroker, Specialized Armament, etc. Other brands are also fine as long as they're mil-spec manufactured, high pressure tested, and magnetic particle inspected like BCM, Daniel Defense, LMT, Spike's, etc. |
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Does anyone know what year Colt decided to make their Carriers with an open bottom? First of all Colt didn't decided those changes, at that time of increased pressure from the government because of the assault rifle import ban of 1989, Colt have to make changes that are acceptable with BATF which are the removal of bayonet lugs, addition of lower receiver sear blocks and the carriers with open bottoms, which we also call as "C" or half moon carriers. The reason for the requirement for the open bottom carriers and steel sear blocks are to prevent the use of illegal Lightning Link (auto disconnector or auto connector), those changes were included by Colt by about late 1990 to 1991, the change did not happen all at once, it went from model to model so there were many variations in the 1990 year production. There was also two versions of the C type carriers, the early version have exposed firing pin and the later version have shrouded firing pin, these carriers was replaced by M16 full auto carriers in 2005 after Colt received approval from the BATFE. http://www.quarterbore.com/nfa/lightninglink.html |
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Does anyone know what year Colt decided to make their Carriers with an open bottom? First of all Colt didn't decided those changes, at that time of increased pressure from the government because of the assault rifle import ban of 1989, Colt have to make changes that are acceptable with BATF which are the removal of bayonet lugs, addition of lower receiver sear blocks and the carriers with open bottoms, which we also call as "C" or half moon carriers. The reason for the requirement for the open bottom carriers and steel sear blocks are to prevent the use of illegal Lightning Link (auto disconnector or auto connector), those changes were included by Colt by about late 1990 to 1991, the change did not happen all at once, it went from model to model so there were many variations in the 1990 year production. There was also two versions of the C type carriers, the early version have exposed firing pin and the later version have shrouded firing pin, these carriers was replaced by M16 full auto carriers in 2005 after Colt received approval from the BATFE. http://www.quarterbore.com/nfa/lightninglink.html Please don't propagate internet myths. Colt didn't HAVE to do any of that, they chose to. The sear blocks were to prevent the installation of drop-in auto sears, the open-bottom carriers to prevent the use of lightning links (AR-15 Auto Connectors). They did away with bayonet lugs on their own, too, before the 94-04 "AW" ban The use of REGISTERED DIAS and LL always has been, and remains legal. The changing of internal dimensions to prevent their use has never been, and is still not legally required by the ATF. The use of full auto carriers is not, and has never been APPROVED by the ATF, who still recommends against the use of any full auto-spec parts in a semi auto firearm. But the ATF's disapproval is not the same as a prohibition. If the gun doesn't fire more than one shot per activation of the trigger, and the auto sear hole has not been drilled, then the combination is not a machinegun, and is legal. |
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Colt didn't HAVE to do any of that, they chose to be proactive and PC. The sear blocks were to prevent the installation of drop-in auto sears, the open-bottom carriers to prevent the use of lightning links (AR-15 Auto Connectors). Thanks for the clarification, I'm not a lawyer just a long time AR enthusiast, but I disagree with your statement that Colt did it to be PC, we both don't have any solid proof to support our points. If Colt didn't voluntarily removed their AR from the market in '89 during the assault import weapons ban and they did not change their lowers to be harder to convert to full auto, there won't be any AR industry today, they would have been banned with the rest of the so called assault weapons. I don'e agree that the sear blocks were only to prevent the installation of drop-in auto sears, the path of the lightning link also have to be blocked by the sear block both at the top of the lower receiver and the bottom of the receiver above the trigger. The changing of internal dimensions to prevent their use has never been, and is still not legally required by the ATF. This is another statement that I don't understand, why does virtually all manufacturers have some form of sear block like narrow lower receiver internal width common to the location of the auto sear, high shelf, and un-machinned web. Why does all manufacturers of semi version of full auto assault rifles have to have their receivers and trigger groups be different from their full auto versions, is it all voluntary or do they have to have ATF approval? Could you show links to support your statements? |
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Colt didn't HAVE to do any of that, they chose to be proactive and PC. The sear blocks were to prevent the installation of drop-in auto sears, the open-bottom carriers to prevent the use of lightning links (AR-15 Auto Connectors). I don'e agree that the sear blocks were only to prevent the installation of drop-in auto sears, the path of the lightning link also have to be blocked by the sear block both at the top of the lower receiver and the bottom of the receiver above the trigger. I didn't say Colt did it JUST for the DIAS, it could have been for the LL too. The changing of internal dimensions to prevent their use has never been, and is still not legally required by the ATF. This is another statement that I don't understand, why does virtually all manufacturers have some form of sear block like narrow lower receiver internal width common to the location of the auto sear, high shelf, and un-machinned web. Why does all manufacturers of semi version of full auto assault rifles have to have their receivers and trigger groups be different from their full auto versions, is it all voluntary or do they have to have ATF approval? Could you show links to support your statements? How about a picture of a semi-auto Colt SP1 milled to M16 specs, but without the sear hole? 
Not a common configuration, but not illegal. You can read more about that stuff in this thread http://www.ar15.com/forums/t_6_17/359991_Still_an_AR_or_Re_Classified_as__NFA__Class_III.html ATF in fact disapproves of (in the sense of not liking, but not in the sense of formally declaring it to be illegal) the use of full auto carriers in semi rifles. However if it doesn't function automatically with the full auto carrier installed, and it doesn't, then it's not illegal, so they cannot actually forbid it. Please consult ATF Publication 5320.8 "National Firearms Act Handbook", page 14 for the full citation on use of unmodified M16 parts in a semi auto rifle. |
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How about a picture of a semi-auto Colt SP1 milled to M16 specs, but without the sear hole? http://i44.tinypic.com/24ou45v.jpg Not a common configuration, but not illegal. You can read more about that stuff in this thread http://www.ar15.com/forums/t_6_17/359991_Still_an_AR_or_Re_Classified_as__NFA__Class_III.html ATF in fact disapproves of (in the sense of not liking, but not in the sense of formally declaring it to be illegal) the use of full auto carriers in semi rifles. However if it doesn't function automatically with the full auto carrier installed, and it doesn't, then it's not illegal, so they cannot actually forbid it. That pic of the SP1 looks like my first AR-15 that I bought new in 1971, I wish I had not sold it and bought an A2 Sporter II rifle. 
Anyway thanks for the link to the NFA forum but the answer in in that same thread, ATF later on increased the thickness of the side walls of the lower receivers. We are now getting way off topic with the OP's and member k6996j questions about Colt carrier types, I answered those questions already correctly because I had back in late 1990 a Colt R6551 Sporter Target rifle and a R6530 Sporter Lightweight carbine, the rifle was not blocked but the carbine had a sear block, both had open C carriers. Bottom line is all the Colt bolt carriers semi and auto would work on current flat top Colt uppers and other mil-spec brands, the full auto carrier works the best as was originally designed by its inventor and I have it in all my AR started in '05, three Colt flat top carbines, an USGI M16A2 Colt upper and a LMT M4 type carbine, all of them runs great, even during bump firing. The NFA link about use of unmodified M16 parts in a semi auto rifle is interesting that the authorities will allow full auto carriers because it doesn't make a semi auto firearm to operate in full auto, but most of us also have full auto upper receivers because of the auto sear cut which are the standard uppers now. Most of us actually have full auto upper half and the authorities might not like it but they're letting us. 
http://www.ar15.com/forums/t_1_6/739614_The_legality_of_an_M16_part_in_your_AR__the_short_version_.html |
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Anyway thanks for the link to the NFA forum but the answer in in that same thread, ATF later on increased the thickness of the side walls of the lower receivers. Negative, Colt later increased the sidewall thickness. Then stuck in sear blocks. Then shaved the carriers. All on their own. ATF did not require them to do so. |
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