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VA, USA
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Posted: 2/29/2024 1:30:22 PM EDT
Have a surplus C7 upper I am working on, inserted a factory Colt barrel and noticed I’m getting minute lateral play between the barrel index pin and notch, before the barrel nut is torqued on.
How much play is acceptable? I am able to fit a .004” feeler gauge between the pin and upper. 
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Posted: 2/29/2024 2:20:58 PM EDT
[#1]
The index pin slot in receiver: .126" +.002"
The index pin hole in extension: .1235" +.0015" I do not have the specs on the index pin itself. |
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LA, USA
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Posted: 2/29/2024 2:31:45 PM EDT
[Last Edit: Dex223]
[#2]
The Index Pin: .1255" -.0005"
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MN, USA
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Posted: 2/29/2024 5:09:12 PM EDT
[#3]
Quote HistoryOriginally Posted By Dex223: The Index Pin: .1255" -.0005" Quote HistoryOriginally Posted By Dex223: The Index Pin: .1255" -.0005" The index pin slot in receiver: .126" +.002" So, on the extreme ends of tolerance, you have +.003" |
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VA, USA
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Posted: 3/1/2024 12:21:39 AM EDT
[#4]
Thanks.
Seems that upper is toast without shimming or some kind of receiver notch repair. Some bubba not only dremeled around the rear takedown lug, but opened the notch up to 0.1315" Some people should not be allowed around any sort of hand tools. |
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MN, USA
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Posted: 3/1/2024 12:45:13 AM EDT
[Last Edit: s4s4u]
[#5]
Quote HistoryOriginally Posted By Apec: Thanks. Seems that upper is toast without shimming or some kind of receiver notch repair. Some bubba not only dremeled around the rear takedown lug, but opened the notch up to 0.1315" Some people should not be allowed around any sort of hand tools. Wondering if the previous barrel had a front sight base? If so, it may have been canted and possibly bubba tried to "index" it? |
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VA, USA
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Posted: 3/1/2024 1:48:03 AM EDT
[#6]
Quote HistoryOriginally Posted By s4s4u: Wondering if the previous barrel had a front sight base? If so, it may have been canted and possibly bubba tried to "index" it? That seems to be the likely case. There was a whole lot wrong with the complete upper/gun this upper receiver came from (original index pin seemed to have been broken/lost, and replaced with a roll pin + barrel nut wasn't torqued to spec), and looks like it turned out to be worse than I imagined. |
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Posted: 3/1/2024 6:47:11 AM EDT
[#7]
Quote HistoryOriginally Posted By Apec: Thanks. Seems that upper is toast without shimming or some kind of receiver notch repair. Some bubba not only dremeled around the rear takedown lug, but opened the notch up to 0.1315" Some people should not be allowed around any sort of hand tools. I don't know that I would call it toast related to the indexing pin. The notch really just serves to idiot proof the barrel installation. As long as the notch doesn't force the barrel out of alignment, it can be shimmed into alignment. The takedown lug is a different story for sure. |
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VA, USA
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Posted: 3/1/2024 4:31:15 PM EDT
[#8]
Quote HistoryOriginally Posted By Homesteader375: I don't know that I would call it toast related to the indexing pin. The notch really just serves to idiot proof the barrel installation. As long as the notch doesn't force the barrel out of alignment, it can be shimmed into alignment. The takedown lug is a different story for sure. Quote HistoryOriginally Posted By Homesteader375: Originally Posted By Apec: Thanks. Seems that upper is toast without shimming or some kind of receiver notch repair. Some bubba not only dremeled around the rear takedown lug, but opened the notch up to 0.1315" Some people should not be allowed around any sort of hand tools. I don't know that I would call it toast related to the indexing pin. The notch really just serves to idiot proof the barrel installation. As long as the notch doesn't force the barrel out of alignment, it can be shimmed into alignment. The takedown lug is a different story for sure. Yeah. Just annoys me that a decent surplus upper got bubba’d in this way. I think I could try to use JB weld to reinforce the rear lug, but not really making a priority of building this upper yet.  
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MN, USA
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Posted: 3/1/2024 5:20:27 PM EDT
[#9]
Quote HistoryOriginally Posted By Apec: Yeah. Just annoys me that a decent surplus upper got bubba’d in this way. I think I could try to use JB weld to reinforce the rear lug, but not really making a priority of building this upper yet. https://i.imgur.com/w1x0der.jpeg https://i.imgur.com/LSSRDlZ.jpeg Looks like bubba had to mod the upper to fit his poorly milled 80% lower  That isn't a super stressful point of contact. Other than the looks, I'd be comfortable with it. Once pinned up, nobody knows 
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Posted: 3/1/2024 5:44:16 PM EDT
[#10]
Quote HistoryOriginally Posted By s4s4u: Looks like bubba had to mod the upper to fit his poorly milled 80% lower That isn't a super stressful point of contact. Other than the looks, I'd be comfortable with it. Once pinned up, nobody knows Quote HistoryOriginally Posted By s4s4u: Originally Posted By Apec: Yeah. Just annoys me that a decent surplus upper got bubba’d in this way. I think I could try to use JB weld to reinforce the rear lug, but not really making a priority of building this upper yet. https://i.imgur.com/w1x0der.jpeg https://i.imgur.com/LSSRDlZ.jpeg Looks like bubba had to mod the upper to fit his poorly milled 80% lower That isn't a super stressful point of contact. Other than the looks, I'd be comfortable with it. Once pinned up, nobody knows Yeah, I'd shoot that. Honestly, JB Weld is almost as Bubba as what's already been done. If you're not going to tig some aluminum into it and mill or file it back, I'd leave it. Maybe put some aluminum black on it. |
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Posted: 3/3/2024 5:23:14 PM EDT
[#11]
Quote HistoryOriginally Posted By TGWLDR: The index pin slot in receiver: .126" +.002" The index pin hole in extension: .1235" +.0015" I do not have the specs on the index pin itself. Kind of odd to me that the index pin isn’t detailed on the barrel extension drawing. |
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VA, USA
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Posted: 3/3/2024 8:08:16 PM EDT
[#12]
I would sell it to someone that doesn’t care about the issues and get another upper. If you are worried enough to ask , you will never be satisfied knowing you have a shit upper.
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LA, USA
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Posted: 3/4/2024 12:08:11 AM EDT
[#13]
Quote HistoryOriginally Posted By alpha0815: Kind of odd to me that the index pin isn’t detailed on the barrel extension drawing. Quote HistoryOriginally Posted By alpha0815: Originally Posted By TGWLDR: The index pin slot in receiver: .126" +.002" The index pin hole in extension: .1235" +.0015" I do not have the specs on the index pin itself. Kind of odd to me that the index pin isn’t detailed on the barrel extension drawing. The index pin has it's own drawing. 
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Posted: 3/4/2024 11:19:28 AM EDT
[#14]
Quote HistoryOriginally Posted By Dex223: The index pin has it's own drawing. Clearly not one I saved when going through the TDP
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GA, USA
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Posted: 3/4/2024 11:26:46 AM EDT
[#15]
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