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Posted: 5/1/2021 1:56:17 PM EDT
[#1]
It is not an oil hole. It is used to retain the front take down pin detent during assembly. This is from 2003 Colt Armor course notes.
18Z50 |
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Posted: 5/1/2021 2:07:24 PM EDT
[#2]
I've always known it as a weep hole, which is a different concept than an oil hole or a retention hole.
I'm sure it can be *used* as a retention hole, with an appropriate tool, but the period factory manuals do not reference it in that way, nor do the period armorer's manuals or factory documentation recommend its use in that manner, so a 2003 retcon by Colt is not definitive. |
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Posted: 5/1/2021 2:25:08 PM EDT
[#3]
If you are talking about small 1/16" hole on the side of the upper mag well it is to aid in the removal of a frozen front pivot pin. It is drilled at the very back of the detent and spring hole and has nothing to do with retaining anything. The earliest reference to it I have been able to find is in the 1968 military repair manual that gives instruction on drilling it and why it is being done. The hole lets the fluid they tell you to soak it in get into the area where the spring and back of the pin are. Maybe they showed it to be drilled also to aid in drainage and venting to avoid avoid corrosion and frozen pivot pins but the instructions do say to drill the hole before soaking the front part of the lower. That is why I figured it was to let the soaking fluid get into the rear areas of the spring hole.
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Posted: 5/1/2021 4:54:16 PM EDT
[#4]
Quote HistoryQuoted: If you are talking about small 1/16" hole on the side of the upper mag well it is to aid in the removal of a frozen front pivot pin. It is drilled at the very back of the detent and spring hole and has nothing to do with retaining anything. The earliest reference to it I have been able to find is in the 1968 military repair manual that gives instruction on drilling it and why it is being done. The hole lets the fluid they tell you to soak it in get into the area where the spring and back of the pin are. Maybe they showed it to be drilled also to aid in drainage and venting to avoid avoid corrosion and frozen pivot pins but the instructions do say to drill the hole before soaking the front part of the lower. That is why I figured it was to let the soaking fluid get into the rear areas of the spring hole. @j3_ - any chance you could post a scan or picture of the instructions to drill it? I have a ban-era AR6700 which didn't originally have the hole drilled for pivot pin detent and spring, and had Specialized Armament drill it a few years ago. They didn't drill the weep hole at that time and I was thinking about having a local smith do it. It just doesn't look right to my eyes. 
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Posted: 5/1/2021 7:23:06 PM EDT
[#5]
I don't know how to get a pic off a pdf page. The drilling the hole and the location is in some of the newer than 1968 military TM manuals also that as easy to find online. I would not drill that hole in a nice lower like that.
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Posted: 5/1/2021 7:26:57 PM EDT
[#6]
PrtScrn while displaying the PDF page will save a screenschot. Option-Shift-3 on a Mac if you don't do Windows.
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Posted: 5/1/2021 9:27:28 PM EDT
[#7]
It came about in 64 or 65 I only know this because there’s a magwell on GB that’s about to end any second now.. it’s a 604 magwell SN 068173 (that dates it to 64-65) with a partial fence with the raised “+” on it as well as the hole in the fence
ETA..  
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Posted: 5/1/2021 10:52:34 PM EDT
[#8]
The 1983 manual at a certain level of maintenance appears to require the hole to be drilled if it is not already there not just when needed for a repair. The hole could have been put in during maintenance. Really hard to know what the revisions on the 1970 print are because of how it just list a reference with no information but there does not appear to be a change for that area so I would say as a guess it was 1970 or earlier for sure on the Colt drawing.
If someone has a access to a copy of the early Colt drawings it might show the revision and date on it. |
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Posted: 5/1/2021 11:19:57 PM EDT
[#9]
Quote HistoryQuoted: @j3_ - any chance you could post a scan or picture of the instructions to drill it? I have a ban-era AR6700 which didn't originally have the hole drilled for pivot pin detent and spring, and had Specialized Armament drill it a few years ago. They didn't drill the weep hole at that time and I was thinking about having a local smith do it. It just doesn't look right to my eyes. https://www.ar15.com/media/mediaFiles/622/right-806333.jpg  Hole diameter is 0.076". A #48 drill bit. So center of hole is 0.922 (0.884 + 0.038) back from the front. I just took this pic using my Colt M4 |
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Posted: 5/2/2021 12:41:29 AM EDT
[#10]
Quote HistoryQuoted: https://www.ar15.com/media/mediaFiles/648/20210501_211132-1926526.jpg Hole diameter is 0.076". A #48 drill bit. So center of hole is 0.922 (0.884 + 0.038) back from the front. I just took this pic using my Colt M4 You can get an out of spec hole location measuring from the wrong place. Both the face you measured off of and the hole location are shown located from the center of the front pivot pin on the drawing. There could be enough difference in the face location tolerance between lowers that using .922" with an unknow face location could place the hole location out of tolerance. |
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Posted: 5/2/2021 1:05:59 AM EDT
[#11]
Quote HistoryQuoted: You can get an out of spec hole location measuring from the wrong place. Both the face you measured off of and the hole location are shown located from the center of the front pivot pin on the drawing. There could be enough difference in the face location tolerance between lowers that using .922" with an unknow face location could place the hole location out of tolerance.  That makes sense it should be indexed off the center of the pivot hole. Thanks! |
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Posted: 5/2/2021 6:48:07 AM EDT
[#12]
Quote HistoryQuoted: It came about in 64 or 65 I only know this because there’s a magwell on GB that’s about to end any second now.. it’s a 604 magwell SN 068173 (that dates it to 64-65) with a partial fence with the raised “+” on it as well as the hole in the fence ETA.. https://i.imgur.com/h7RA0mK.jpg https://i.imgur.com/tWhHVU6.jpg I have two full fence xm16e1 and no hole |
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Posted: 5/2/2021 10:57:52 AM EDT
[#13]
Quote HistoryQuoted: I have two full fence xm16e1 and no hole Yeah, I have full fence XM myself and that one doesn’t have a hole either, it is possible like mentioned earlier some rifles were retro fitted with it later? |
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Posted: 5/2/2021 11:53:52 AM EDT
[#14]
Is the hole literally to keep the detent from going into orbit? Was this change required by NASA?
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Posted: 5/2/2021 2:24:34 PM EDT
[#15]
Quote HistoryQuoted: It is not an oil hole. It is used to retain the front take down pin detent during assembly. This is from 2003 Colt Armor course notes. 18Z50 Sorry, but that just isn't true. If you were instructed that, the instructor was in error... While it's nearly become an "AR-15 Urban Legend" the hole on the fence can't retain anything except the tail of the detent spring. If you look at the below pic, it shows that the tail of the spring only goes past the hole by ~0.18" (The bottom of the hole is the right edge of the green tape). How would this retain the detent? It can't and it doesn't.  Here's a pic of the "Pivot Pin Detent Installation" section from the Colt M16A2 Rifles and Carbines Armorers/Depot Maintenance and Repair Manual, Second Edition 1991, Copyright date 2004. This is the technique that I recall Colt teaching in that era, and I don't imagine it has changed.  For anyone who might care, here's the removal instructions-  Again, no mention of the hole on the fence in either the assembly or disassembly instructions. The hole is for maintenance of the spring and detent. It allows any water to escape, and it allows you to keep it lubricated and moving freely. It serves no purpose in assembly or disassembly. |
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Posted: 5/2/2021 2:56:28 PM EDT
[#16]
So we can screw a Zerk fitting into it?
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Posted: 5/2/2021 3:20:51 PM EDT
[#17]
Quote HistoryQuoted: If you are talking about small 1/16" hole on the side of the upper mag well it is to aid in the removal of a frozen front pivot pin. It is drilled at the very back of the detent and spring hole and has nothing to do with retaining anything. The earliest reference to it I have been able to find is in the 1968 military repair manual that gives instruction on drilling it and why it is being done. The hole lets the fluid they tell you to soak it in get into the area where the spring and back of the pin are. Maybe they showed it to be drilled also to aid in drainage and venting to avoid avoid corrosion and frozen pivot pins but the instructions do say to drill the hole before soaking the front part of the lower. That is why I figured it was to let the soaking fluid get into the rear areas of the spring hole. When in 68 did the manual come out? |
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Posted: 5/2/2021 4:34:53 PM EDT
[#18]
Also does anyone know when colt started doing it at the factory? Or if it was just always an armorer level modification?
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Posted: 5/2/2021 6:51:34 PM EDT
[#19]
Quote HistoryQuoted: When in 68 did the manual come out? The front page says August 1968 inside page says current 22 July 1968 and bottom of page says supersedes August 1966 manual. But this hole is an add on in the field maintenance thing. If I was going to put a hole in a lower, which I would not do, I would located it off the Gov. lower print which is a slightly different size hole and location for the hole. |
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Posted: 5/2/2021 7:02:43 PM EDT
[#20]
Quote HistoryQuoted: The front page says August 1968 inside page says current 22 July 1968 and bottom of page says supersedes August 1966 manual. But this hole is an add on in the field maintenance thing. If I was going to put a hole in a lower, which I would not do, I would located it off the Gov. lower print which is a slightly different size hole and location for the hole. Did colt ever do it at the factory? |
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Posted: 5/2/2021 7:44:32 PM EDT
[#21]
Quote HistoryQuoted: Did colt ever do it at the factory? I don't know much of anything about the when or who of retro stuff. I just noticed the question about the hole and remembered seeing it in the 68 manual when I looked through it a couple years ago. |
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Posted: 5/2/2021 7:51:11 PM EDT
[#22]
Quote HistoryQuoted: Did colt ever do it at the factory? Almost certainly - I've seen way too many lowers with nicely anodized weep holes for even a fraction of them to have been done in the field. It probably became a factory process for military contracts not long after those 1968 manual updates @j3_ references. |
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Posted: 5/2/2021 8:18:23 PM EDT
[#23]
Quote HistoryQuoted: I don't know much of anything about the when or who of retro stuff. I just noticed the question about the hole and remembered seeing it in the 68 manual when I looked through it a couple years ago. Ah ok sounds good. |
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Posted: 5/2/2021 8:18:54 PM EDT
[#24]
Quote HistoryQuoted: Almost certainly - I've seen way too many lowers with nicely anodized weep holes for even a fraction of them to have been done in the field. It probably became a factory process for military contracts not long after those 1968 manual updates @j3_ references. Quite possibly |
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Posted: 5/3/2021 12:03:59 AM EDT
[#25]
Quote History@j3_ - any chance you could post a scan or picture of the instructions to drill it? I have a ban-era AR6700 which didn't originally have the hole drilled for pivot pin detent and spring, and had Specialized Armament drill it a few years ago. They didn't drill the weep hole at that time and I was thinking about having a local smith do it. It just doesn't look right to my eyes. https://www.ar15.com/media/mediaFiles/622/right-806333.jpg From Colt's lower receiver drawing for the M16A1, that hole is .078" dia. and 1.055" (+/- .010") from the center of the Pivot Pin. (I can post a scan when I get to my other computer on Monday) |
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Posted: 5/3/2021 4:13:21 AM EDT
[#26]
Quote HistoryQuoted: Almost certainly - I've seen way too many lowers with nicely anodized weep holes for even a fraction of them to have been done in the field. It probably became a factory process for military contracts not long after those 1968 manual updates @j3_ references. I am sure that it was done in the factory, had over 70x m16a1 in various configurations many new all holes were anodized. |
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Posted: 5/3/2021 9:23:22 AM EDT
[#27]
Edited. Whole manual link is in another post now.
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Posted: 5/3/2021 9:40:22 AM EDT
[#28]
If anyone else is looking, I found a link in the archives to a copy of the August 1968 version of the manual.
https://drive.google.com/file/d/0B9hAva_yxlzPNnc1Sktvd3ZIN1E/view |
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Posted: 5/3/2021 10:16:05 AM EDT
[#29]
Quote HistoryQuoted: What is a cabity? I believe they mean "cavity". The b is right next to the v on the keyboard... If you refer to the installation instructions I posted above, Colt still refers to it as the "detent cavity". |
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Posted: 5/3/2021 11:06:53 AM EDT
[#30]
Quote HistoryQuoted: If anyone else is looking, I found a link in the archives to a copy of the August 1968 version of the manual. https://drive.google.com/file/d/0B9hAva_yxlzPNnc1Sktvd3ZIN1E/view Hip fire was still a thing then, apparently. |
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Posted: 5/3/2021 11:23:22 AM EDT
[#31]
Quote HistoryQuoted: Here is the section about the repair and the hole. The figure is on another page. I decided not to post it because it is in error for something made to current drawings. Might have been okay for the measurements on an early drawing. Because of the large tolerance of the hole depth on current Gov. drawing placing a hole where the figure shows on a lower made to minimum hole depth and maximum face dimension from the front pivot could miss the back end of the spring cavity by a few thousands. Not the only mistake. What is a cabity? https://www.ar15.com/media/mediaFiles/1642/frozenpinfix_png-1927849.JPG Cool thanks |
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Posted: 5/3/2021 12:35:18 PM EDT
[#32]
I did not see anything about the hole in the 1966 manual referenced on the bottom of the chapter page. I found a copy of it at smallarmsreview.
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Posted: 5/3/2021 1:16:34 PM EDT
[#33]
Quote HistoryQuoted: I did not see anything about the hole in the 1966 manual referenced on the bottom of the chapter page. I found a copy of it at smallarmsreview. Was there 67 manuals? |
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Posted: 5/3/2021 2:48:31 PM EDT
[#34]
Quote HistoryQuoted: From Colt's lower receiver drawing for the M16A1, that hole is .078" dia. and 1.055" (+/- .010") from the center of the Pivot Pin. (I can post a scan when I get to my other computer on Monday) This is correct. William |
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