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MN, USA
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Posted: 5/1/2024 6:27:59 PM EDT
Does anybody provide bushing installation services for pivot and take down pin holes that are worn and sloppy? I have a surplus salty Colt Keyhole M4 upper I would like to get back into specs. The pivot pin hole is worn to where I can slop the upper back and forth. Would it just be an annoyance to install a barrel and shoot it like this since the bolt will be headspacing off the barrel extension. I currently have some HVAC aluminum tape installed in the holes which takes most of the slop out. Looking for a more permanent solution.
John Thomas with Retro Arms Work used to provide this service but no longer does. |
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Posted: 5/1/2024 6:43:42 PM EDT
[Last Edit: EdgecrusherXES]
[#1]
Could shimming possibly resolve your problem?
How much slop are we talking? |
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Posted: 5/1/2024 6:49:02 PM EDT
[#2]
Accuwedge may tighten your upper/lower fit. Also Aero Precision lowers come with a nylon-tipped set screw coming up through the grip that can be used to tighten the fit.
For a permanent solution, a good machinist would be able to bore out and sleeve the holes, but I'd just swap uppers before I'd go to all that trouble. |
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Posted: 5/1/2024 6:54:35 PM EDT
[#3]
I used a shoulder bolt from the hardware store. Tightened down the screw that goes into the shoulder bolt until there was ZERO play between upper and lower. Shoulder bolt washers and all cost about $3.00. Shoulder bolts are precision ground, I just had to file a wee bit off one end...worked like a champ!!
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Posted: 5/1/2024 7:22:05 PM EDT
[#4]
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Posted: 5/1/2024 9:16:17 PM EDT
[#5]
I know jp rifles sells oversized pins but I don't know if they would end up too tight in the lower.
https://www.jprifles.com/buy.php?item=JPTDP-223-SET |
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TN, USA
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Posted: 5/1/2024 9:26:15 PM EDT
[#6]
Quote HistoryOriginally Posted By Nobody69s: I know jp rifles sells oversized pins but I don't know if they would end up too tight in the lower. https://www.jprifles.com/buy.php?item=JPTDP-223-SET https://www.jprifles.com/buy.php?item=JPTDP-223F https://www.jprifles.com/buy.php?item=JPTDP-223R |
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NV, USA
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Posted: 5/2/2024 6:22:51 AM EDT
[#7]
Originally Posted By TW56: The pivot pin hole is worn to where I can slop the upper back and forth. So in the pivot shims thread, we discovered a excellent combo for eliminating play/slop. The Pivot Shims eliminate side to side (3-9 o'clock) play. The Wheel Diamond Shim eliminates up-down (6-12 o'clock) play, as well as rotational wobble (twisting the handguard causing the upper to rotate slight counter clockwise).  However, when you say upper 'back and forth,' are you describing one of the above (3-9; 6-12; rotational) directions? Or is it that the upper is moving forward and backward, ie that the upper can slide a bit toward the muzzle / back toward the stock? |
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Posted: 5/2/2024 6:45:44 AM EDT
[Last Edit: Wangstang]
[#8]
Just confirming since you mentioned it's a colt upper, are you using an upper that has an enlarged pivot pin hole or a Milspec pivot pin hole? JT's bushing work was usually to convert large pin colts back to milspec for use in retro builds.
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MN, USA
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Posted: 5/2/2024 12:24:53 PM EDT
[#9]
Quote HistoryOriginally Posted By spydercomonkey: So in the pivot shims thread, we discovered a excellent combo for eliminating play/slop. The Pivot Shims eliminate side to side (3-9 o'clock) play. The Wheel Diamond Shim eliminates up-down (6-12 o'clock) play, as well as rotational wobble (twisting the handguard causing the upper to rotate slight counter clockwise). https://i.ibb.co/nz2K78s/AR15-LWRC-Shims-Combo.jpg However, when you say upper 'back and forth,' are you describing one of the above (3-9; 6-12; rotational) directions? Or is it that the upper is moving forward and backward, ie that the upper can slide a bit toward the muzzle / back toward the stock? The pivot pin hole size allows it to slide a bit from the muzzle to the stock. |
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MN, USA
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Posted: 5/2/2024 12:31:03 PM EDT
[#10]
Quote HistoryOriginally Posted By Wangstang: Just confirming since you mentioned it's a colt upper, are you using an upper that has an enlarged pivot pin hole or a Milspec pivot pin hole? JT's bushing work was usually to convert large pin colts back to milspec for use in retro builds. No it is a C Keyhole M4 marked "milspec" upper receiver, not a large pin Colt upper. John Thomas formerly offered bushing service to convert large pin Colt's to Milspec makes more sense then fixing sloppy worn pivot pin holes. I will try some pivot pin shims and some large diameter pins to see how much slop I can take out. I already have some Griffin pins mentioned to try. Is there any thing unsafe about back and forth slop or is it a OCD issue? |
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VA, USA
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Posted: 5/2/2024 7:40:04 PM EDT
[#11]
Quote HistoryOriginally Posted By TW56: No it is a C Keyhole M4 marked "milspec" upper receiver, not a large pin Colt upper. John Thomas formerly offered bushing service to convert large pin Colt's to Milspec makes more sense then fixing sloppy worn pivot pin holes. I will try some pivot pin shims and some large diameter pins to see how much slop I can take out. I already have some Griffin pins mentioned to try. Is there any thing unsafe about back and forth slop or is it a OCD issue? Generally speaking after inserting a magazine it’ll tighten up. So the play is merely ocd most of the time but understandably concerning. So long as it doesn’t move forward or up and down then you’re probably good to go. Did you try shooting it yet? That would be the real test. |
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VA, USA
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Posted: 5/2/2024 7:47:17 PM EDT
[#12]
Also slop might play into accuracy. Some people say it does others don’t. I suppose if you want a super accurate build where you’re taking it to matches then you’ll probably want something that is tight fitting. Otherwise you’d get man sized targets easily with it.
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NV, USA
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Posted: 5/2/2024 9:33:45 PM EDT
[Last Edit: spydercomonkey]
[#13]
Quote HistoryOriginally Posted By TW56: The pivot pin hole size allows it to slide a bit from the muzzle to the stock. Quote HistoryOriginally Posted By TW56: Originally Posted By spydercomonkey: So in the pivot shims thread, we discovered a excellent combo for eliminating play/slop. The Pivot Shims eliminate side to side (3-9 o'clock) play. The Wheel Diamond Shim eliminates up-down (6-12 o'clock) play, as well as rotational wobble (twisting the handguard causing the upper to rotate slight counter clockwise). https://i.ibb.co/nz2K78s/AR15-LWRC-Shims-Combo.jpg However, when you say upper 'back and forth,' are you describing one of the above (3-9; 6-12; rotational) directions? Or is it that the upper is moving forward and backward, ie that the upper can slide a bit toward the muzzle / back toward the stock? The pivot pin hole size allows it to slide a bit from the muzzle to the stock. Wow, so a new direction of play that we didn't solve in the pivot shim thread. I don't know what, other then the suggested extra wide takedown pins, would work there. If that doesn't work, perhaps painting the inner hole of the upper pivot with a thinned out nail polish to tighten the fit? I'm concerned that direction of play could perhaps impact how hard the hammer hits the firing pin, but no idea. It definitely seems like a more woriesome play direction then the 12-6 / 3-9 play we normally associate with AR slop. |
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PA, USA
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Posted: 5/3/2024 1:29:17 PM EDT
[Last Edit: Smith-16]
[#14]
Quote HistoryOriginally Posted By TW56: No it is a C Keyhole M4 marked "milspec" upper receiver, not a large pin Colt upper. John Thomas formerly offered bushing service to convert large pin Colt's to Milspec makes more sense then fixing sloppy worn pivot pin holes. I will try some pivot pin shims and some large diameter pins to see how much slop I can take out. I already have some Griffin pins mentioned to try. Is there any thing unsafe about back and forth slop or is it a OCD issue? Your buffer retainer might take a beating/break if the carrier is not depressing the buffer slightly. Wouldn't headspace be fine as long as the bolt remains in the locked position? |
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