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Posted: 7/25/2006 6:14:26 AM EDT
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Wondering if anyone has permanently modified a Large Hole Colt Slabside SP1 Lower into a Small Hole Lower? Why? Because for a Model 601 or 602 Build the various adapters that must be used are not technically correct and IMHO they look like crap, not to mention they can be a pain to use. I am looking at having some round stock welded in place to fill in the existing large holes and then having a new small hole properly located and drilled. So am I crazy for considering the permanent modification of a Colt SP1 Lower, probably, but sometimes you just gota cross the line!  If anyone else has crossed that line with good or bad results please jump in. Also, given the Lower would have to be welded: 1. Wondering if there is a positive way to ID which of the Lowers are made from 7075 versus 6061. Is there a given serial number break/cut off point? 2. Is there a positive way to identify the Lowers that were made using the "Hot Pressed Casting / Forging" process? Both of those could have severe impacts on an attempted welding process, as in it would not work! As such I need to make sure that I have a Forged 7075 Lower to start with. This should also be similar to permanently modifying a Large Hole Upper, if anyone has any experience with that. Thanks in advance, "Capt Richardson" |
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I have contemplated such a conversion but using press in bushings instead of welding. I have thought of a variety of ways to retain the bushings. 1: Drill a hole from the mag well and into the bushing but do not break out into the pivot pin bore. Use a small roll pin to retain the bush. Peen over the roll pin hole in the magwell. 2: Bevel the original pivot pin holes on both surfaces [ 4 surfaces to be beveled ] and insert solid alum stock in the hole and using a press or even a small hammer forge the alum stock until it fills the bevels and locks into place. Then drill the hole for the new location. 3. .001 or .002" interference fit the predrilled bushings, heat up the lower and freeze the bushings and install with Loctite bushing retainer. You would have to trial fit and make reference marks so that the bushings could be installed correctly. You might not even need the interference fit. I have used some of the various bushing "loctite" on the pinion gears of elec RC aircraft motors and the stuff is amazing. On all of my 'cogitating' I have wanted to avoid permanent mods to the SP1 lower and also avoid having to refinish it. rj |
More Power to you Capt! You are giving that wanabe SP1 it's ultimate dream! To be a real small hole lower! Oh yeah I would like to see it when it is done as well. |
Why not just get a small hole lower and grind off the entire mag fence, get a small hole slabside upper (or use an adaptor bushing) and get a .250" pushpin? Buuuut I doubt any of us is gonna talk you outta this  so good luck to you and sorry I can't be of anymore help 
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| I've seen it done with inserts (maybe brass??) epoxied and drilled. Did not need refinish. The .312 screw was then turned down on a lathe to .250 The modification looked very clean. It was done a long time ago before anyone had ever thought of those adapters cause the guy wanted to use an M16 upper on his AR15! I think if done correctly it could even add value to your reciever. |
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Thanks for all of the feedback. I think the "Mythical Status" of the SP1 is largely mythical. No question that when the ban was on that they were very sought after and people paid dearly for them. I can appreciate the value and collectability of a very early one, but IMHO when you really want to get down to it the later ones are really just another AR. Don't get me wrong they are a high end AR, but truth of the matter is there are thousands of them out there so they are not exactly a rare collectible. My goal for the 601 rebuild is to be as "Technically / Historically Accurate" as I can be without going the NFA route. As such a Colt Slabside Lower would be the most accurate. The Markings will not be 100%, but I may also work on modifying those as far as I can go without getting into to legal trouble. For accuracy purposes I also plan on using a 601 Pivot Pin, which would make some form of Large Hole to Small Hole modification necessary. I like the bushing/insert route, especially if it could be done without having to do a major refinish job on the Lower. My only concern with this route would be appearance and the durability over the long run. I think I am going to give this a shot first and see how it goes. If it does not work then no big deal I can simply drill everything out and go the welding route. I will make sure to document everything as I go, hopefully this may turn out to be of some value in future builds. Thanks again, stay tuned, "Capt Richardson" |
| Ya know..maybe you could take a large-to-small hole bushing that fits inside the upper and cut it in half and then weld or locktite each of the halves onto the lower...then you could use the small hole pivot pin. And if you used locktite, you wouldnt have to permanantly modify it and it would probably hold for as long as you wanted it to. I have a bushing that I dont use anymore and if you need one to experiment on this with, I'll send it to you free of charge. The cutting it in half may be a little tricky since they're kinda thin but it'd be worth a shot wouldnt it? Let me know if you need one. |
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Capt. go ahead and do it. Many, many of the converted SP-1's have already had this modification done. Below is a link to a guy that does the bushing job. No refinish necessary and I honestly think that any of the pins you would use will cover it. Go to the site below and select "M16 AR-15" and then on that page you will see a link for the large hole to small hole conversion. http://m60joe.com/ There are also several C2 manufacturers that offer the service to resize it, but that requires refinish and is permenant. |
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Thanks again for the info, Nice to see that someone else is already doing the modification. That modification on M60JOE is basically what I am looking at doing. The only difference is I will drill the hole for a set pin through the magwell so it will be invisible from the outside. On the "value of this", I paid $750 for the SP1, I can sell the Upper for $350 to $400 (or use it for another build), so then I have $350-$400 tied up in the Lower. The cheapest I am going to get into a complete Lower is about $250, then add to that the cost of converting it to A1, and it would be at least $350. Basically it is wash. If you are paying $1,200 for a SP1, then shop around, there have been multiple ones auctioned off recently in the $800 price range. There are a lot of SP1's listed in the $1,200-$1,500 but no one seems to be to interested in buying them unless they are in the very early serial number range. IMHO, if you are going to go to the trouble of building a 601 Replica, you might as well go for accuracy! The build starts this weekend, say a prayer for me and the SP1! "Capt Richardson" |
I disagree. By modifying you lower, you aren't making it any more accurate by adding: Sleeves Bushings New holes for roll pins or setscrews Bushing adhesive TIG Welding Refinishing None of this stuff came with a real 601 lower from the factory. These efforts you guys are talking about should be concentrated on having real forged retro lowers made. |
No offense, but I still think his mod looks crappy. If it were me, I'd go ahead and weld, redrill, and refinish. If it really came down to it, you could just redrill the large hole again later to put it back the way it was. The thing is, it's YOUR lower. Why compromise because other people might not like it? If you're going to do it, do it right. You can't take it with you, and like they say, you only go around once in life... go for the gusto! A proper and complete modification would look AWESOME, not like a half-assed job where you can still see the bushing after all is said and done. It's like restoring a car. There are many ways to do it, and there will always be those who don't seem to approve of how it was done. YOU are the owner, and it should be done in a way that you will be pleased with yourself. It's not as if you are butchering the first AR ever made. Besides, it could easily be restored to the original large hole configuration, as I already mentioned. Again, no offense intended; just my take. Good luck with it, Cap'n! 
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That would be ideal, but is it realistic? What about 80% 601 castings? |
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Bottomline is that as of right now, no one is going to make an accurate forged lower. Even if they do it will not have the Colt or Armalite Logos, so you have to do what you can. Following the logic that no attempt is good enough, how is any attempt or any rifle retro built good enough if it is not full auto? To me a bushing behind a pin or a weld over and refinish is MUCH less obvious than SAFE, SEMI, AUTO missing or the obvious sear pin on the right side, much less model designations, etc. If this is what Capt. wants to do and it makes him happy, power to him! If he wants to share his excitement amongst friends and like minded people, that's fine to. I just don't see the point in kicking him in the balls when there is NO OTHER option open for him. This reminds me of the guy on Subguns that gets the big "no Thompson is a real Thompson if it was made after WWII" thread rolling every couple of months. If you don't have anythign nice to say, don't say anything at all.... By the way Capt. if you want to do the pin conversion for real, Mike Klos will do it for $250 including refinishing and he does bad ass work. http://www.american-manufacture.com/ |
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I would consider installing one of the offset pins with the two screws. The inside pin will be able to adapt the correct .250 601 upper to the .312 lower. Here's what I would do differently though. Instead of using the two screws to secure the upper to the lower, I would machine some small replacements that would mimic the 601 pin. No, it won't be a push pin, but who would know the difference from a photo? Or handling it for that matter? The replacement parts would consist of a "pin head" of appropriate size for the right side and a "pin end" with the appropriate center drill for the left side. My plans for my 601 (built on an SP1) will be to use one of the .312 push pins that has been slightly modified to suit my taste. Stay tuned... 45 Bravo out |
Scott, If it does not have the Colt Markings how is it a "Real Forged Retro Lower"? I don't see Colt doing the work, and I don't see them licensing their markings. I guess you could attempt to replicate the markings yourself, but that would be some serious work, and potential legal liability. So what is more realistic a modified Colt Lower, or a "Retro Reproduction Lower" without any type of Colt Markings? Neither are 100% realistic, but I can make the Modified Colt Lower a reality a hell of a lot quicker than anyone is going to make a "Real Forged Retro Lower" a reality! I am all for the "Real Forged Retro Lower", but I honestly can't see that happening anytime soon, if it will ever happen at all. I am actually still working on that issue, but at this point there are a hell of a lot of issues that have to be resolved before anyone is going to be producing them. Speaking in general on the modification, I mocked up the Lower last night using the bushings that are used to convert a large hole upper to a small hole upper, and it looked like crap. There is a very noticeable gap between the bushing and lower which would have to be filled in. I am not a big fan of putties or fillers, so I say it is time to break out the welder and make the bushing and lower one. This will require a refinish of the Lower, but that just means that I can also have the SP1 markings welded over, and some other minor mods made. Not sure at this point if the refinish will be Anodized or Norrells. I am also going to have to refinish the 601 Upper, it has the "Black Arsenal Finish", so whatever route I go I will have them matched up. I can't weld on aluminum, so I will be shipping this one off for someone else to do the work. I will try to get them to document the process as best they can. I will definitely be able to at least post some before and after shots. Thanks again to everyone for the input, "Capt Richardson" |
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To answer the original question; Yes. I've done it to my SP1 XM177E2 clone. Simple and inexpensive. I used two of the inserts that DPMS sells for small holing large hole uppers. Cut them to length for the wings on the lower. Since the rifle has a forward assist large hole upper as well, I also small holed it. Toal investment, about $12.00. For the moment, I'm using the KNS push button takedown pin, but I may go ahead and also get the DPMS version, which doesn't have the push button and so looks a bit more "original" than the KNS version. It's aluminum rather than steel, which is the main reason I didn't get it in the first place, but for the $5 it costs, I'll probably tack one onto my next Brownell's order.  Now my reason for going to the 1/4 inch version may not be quite the same as others. My SP1 is class 3'd, and I wanted the opportunity to swap over to my M4 type upper assy, without having to fiddle with the offset adapter. After nearly 30 years, the barrel on the 177 clone is getting kind of tired, and I'd like to save it to the extent possible The DPMS inserts are slightly offset, and the thin side goes up top. While the inner diameter is spot on for the 1/4 inch pins, the external diameter is just a bit small; which I assume is to allow you to coat the thing w/a thick epoxy based adhesive, and set them into the original hole. And while I was at it, I made the right side sleeve short enough that the pin is retained on the lower whaen it's pulled out to release the upper. Beats the hell out of paying someone $250 to put a welding torch on it----and does he re heat treat the whole lower afterwards??So far, everything is working just fine. I can drop my M4 type upper, and my son's flat top featherweight upper onto the lower, and experience full auto fire w/the newer type uppers.
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I'd say the $350 stock was a Total Silence XM607 |
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Thanks again to everyone for all of the great feedback! Per the other folks, pics of any of the Mods would be great! I have a bit of a predicament now thanks to RJAY, my SP1 Lower does not have the pre 1977 "Colt's Patent Firearms Mfg Co" rollmark. Now I have to decide if it is worth going after a Lower with the proper markings, or if I just learn to live with what I have. Thanks a lot RJAY! Ignorance was bliss! Keep up the great retro build efforts, "Capt Richardson" |
It'll never be 100% perfect, Capt... I'd just go with what you have. However, if you wish to search out the proper SP1 lower, I will GLADLY purchase the one you have. *innocent whistle* (What can I say, I have a slickside a1 upper, triangle handguards and a1 fh that I absolutely refuse to mate to an A2 lower)
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I am not nearly as bad an O/C Perfectionist as I used to be but small details do, unfortunately, jump out at me. rj |
Are you not able to see RJAY's second post on Page 1  The text and picture are working for me. "Capt Richardson" |
Thanks for not abusing/disrespecting that Slickside A1 Upper, I am sure that it will thank you for trying to find it a proper/respectful home! I am looking to see if I can find the proper lower at a "reasonable price", if I do I will let you know. Best of luck with your Lower search. "Capt Richardson" PS: thanks to everyone else for sharing your info, all of the feedback on this has been great! |
I live by the "If you're going to do it, might as well do it right." philosophy. And, thanks. |
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I found some photos of this on M60Joe's website.users.zoominternet.net/~picplace/coltpivotpinbushings.jpg Does not state how it was done, but at least you can see a finished product. Looks to have either two small roll pins or set screws at the bottom of the sleves installed. |
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