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Jackp
Veteran Member


USA
1064 Posts

Posted - 07/04/2018 :  3:31:30 PM  Show Profile Send Jackp a Private Message  Reply with Quote
For some time, I have endeavored to locate copies of original part drawings for the M1 Carbine. I was hopeful that these drawings would contain the revision history of drawing changes so that I could determine the exact date and reason for each change. However, it looks like such details may be lost. Some of the drawings I found have had the revision data redacted. Other drawings just say "revised and redrawn" without describing the change.

However, these drawings are useful in answering some of the questions that come up on this and other forums. There are two main sources for detailed drawing information.

One is Jerry Kuhnhausen's, "The U.S. .30 Caliber Carbines Shop Manual", available on Amazon. This 224 page book contains elements of the Ordnance drawings for the M1 Carbine but these drawings are not really complete. They are "new" drawings made by the book publisher containing partial details of the original Ordnance drawings. They do not contain all of the necessary dimensions from the original Ordnance drawings. I was unable to answer many of the common questions that have been asked on this and other forums using only this resource.

A second and superior source of detailed drawings is Eric Nicolaus' book "Carbine, Cal. .30 M1: Diagrams & Pictures" available on his web site. This book contains the latest complete detailed drawings of all the carbine parts along with related assembly drawings. These drawings were obtained by the author from the National Archives and cleaned up to make them legible in his book. The revision blocks are intact on these drawings but there is no way to link them to any available description of the change itself. It's possible that the details of these revision changes are also available in the National Archives but that would require investigations that I'm not prepared to undertake.

Listed below are many of the questions that have appeared in this and other forums that can be answered by these drawings:

1) What is the height of the front sight blade on an unfiled sight? This comes up when issues occur with POI regarding switching from flip sight to adjustable sight. .785” min. from centerline of bore or 1.115” (This is a typo correction, was 1.155") from bottom of sight (Type 1 only. Type 2 sights will be ~.015" taller.)

2) Is the receiver dovetail tapered from left to right? We are always told to install rear sight from right to left and remove from left to right. Although TM9-1276 (1947 issue) says that the dovetail is tapered, the detailed Ordnance drawings of both the receiver and rear sights show no such taper. This mention of taper is not present in later issues of the tech manual. Also, measurements of actual receivers and rear sights show no such taper. The only other apparent reason to remove sight from left to right is to avoid interference with windage knob.

3) What is the radius of the recoil plate shoulder in the stock? Robert W. Irwin stocks frequently have a distinctive gap resulting from a smaller .125 radius. .25” Radius

4) What is the clearance between the stock and inertia block of the operating slide? FTF’s are sometimes caused by inertia block rubbing inside of the stock. .055” min, .085” max or .0275” to .0425” per side when centered.

5) What is the diameter of the safety hole in the trigger housing? A collector reported failure of the safety resulting in excessive trigger wear causing automatic fire. .312” DIA +.002

6) What is the barrel diameter? Often a question when fitting a new front sight. .600” DIA -.005 at barrel band, .5800” DIA -.0025 at front sight.

7) What is the clearance between the hammer and slot in the bolt? This is a feature of design that prevents out-of-battery discharges. .004” min, .009” max.

8) What is the width of the rear tab on the operating slide? Often suspected of causing the slide to unexpectedly disengage from the receiver. .090” -.003

9) How long is the firing pin? Suspect cause of light primer strikes. 2.957” -.004

10) What is the width of the tab on the recoil plate? Loose fit affects accuracy. .47” -.02 (Wartime issue only. Post war RIA recoil plate measures .438).

11) What is the width between receiver lugs that recoil plate fits into? See #10. .530” +.003

12) What is the length of the recoil spring? Suspected cause of FTF’s 10.28”

13) What is the clearance between the receiver sides and the inside of the stock? Potential cause of poor accuracy. .015” -.0025 per side

JackP

Edited by - Jackp on 07/31/2018 10:35:58 AM

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boomer656
Greenhorn Member



USA
47 Posts

Posted - 07/04/2018 :  5:35:42 PM  Show Profile Send boomer656 a Private Message  Reply with Quote
That's a lot of really good info! Thanks for sharing.
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Tuna
Moderator



3306 Posts

Posted - 07/04/2018 :  6:21:29 PM  Show Profile Send Tuna a Private Message  Reply with Quote
Your # 2 is wrong. It was tapered to prevent the rear sight from moving under recoil. There was no adjustable knob when the system was designed. Those companies that thought it might move then used a chisel type stake to prevent it from moving to the right. The type 1 flip sight was the standard sight from the beginning of production till early in 1944.
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Jackp
Veteran Member



USA
1064 Posts

Posted - 07/04/2018 :  6:58:05 PM  Show Profile Send Jackp a Private Message  Reply with Quote
According to the original Ordnance drawings there is no taper on either the receiver dovetail or the sight dovetail. Both are straight across. If they are machined to the tolerance specified in the Ordnance drawing there will be .0015 min to .0045 max interference fit considering both minimum and maximum material conditions. Perhaps that is why the flip sight was chisel staked. Also, the radius of the edge of the sight dovetail and the root of the receiver dovetail are specified in a manner to ensure that the fit is determined by the flat surface of the dovetail and not by the sharp edge of the dovetail. I believe this to be true as evidence by all the type 1 flip sights that I have seen that are installed backwards. If it were tapered, this shouldn't be possible.


BTW, Happy Independence Day!

JackP

Edited by - Jackp on 07/04/2018 7:08:35 PM
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Tuna
Moderator



3306 Posts

Posted - 07/04/2018 :  9:31:35 PM  Show Profile Send Tuna a Private Message  Reply with Quote
Sorry Jack but there is a slight tapper and it was done just to help center the rear sight and to not let it slip from shooting. The drawings may say one thing but the actual manufacturing is another. Not the first time that reality and ordnance differed on something. Try and find a carbine that needs a new rear sight. Try pushing it into the dove tail and what happens Does it stop well before being in all the way? Yes it will as the sight has to be fitted to the dove tail as there is a tapper.
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Jackp
Veteran Member



USA
1064 Posts

Posted - 07/04/2018 :  11:40:19 PM  Show Profile Send Jackp a Private Message  Reply with Quote
Tuna, I have revised my original post to reflect additional findings regarding dovetail taper. The amount of interference fit (up to .0045") may result in deformation of the dovetail during assembly that may be interpreted as taper. TM9-1276 (page 65) indicates that relatively great force may be required to install the rear sight using the recommended assembly tool. Up to 54 inch-pounds of torque could be applied during assembly possibly causing deformation.

JackP
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BEYU
Advanced Member



USA
309 Posts

Posted - 07/05/2018 :  4:08:53 PM  Show Profile Send BEYU a Private Message  Reply with Quote
I bought a book of technical drawings from CMP a few years ago. The book is titled: "Carbine, Cal. .30, M1: Diagrams & Pictures First Edition"

It is available elsewhere at $40. Here is a link:

You must be logged in to see this link.

BEYU

"Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety."

- Benj. Franklin
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Jackp
Veteran Member



USA
1064 Posts

Posted - 07/05/2018 :  4:32:17 PM  Show Profile Send Jackp a Private Message  Reply with Quote
BEYU, that's the book I referenced in my original post. Eric has done an excellent job of cleaning up old Army Ordnance drawings from the National Archives. Too bad that the revision history is not available. With that we could determine exact dates of implementation of changes.

JackP
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BEYU
Advanced Member



USA
309 Posts

Posted - 07/07/2018 :  12:47:56 PM  Show Profile Send BEYU a Private Message  Reply with Quote
quote:
Originally posted by Jackp

BEYU, that's the book I referenced in my original post. Eric has done an excellent job of cleaning up old Army Ordnance drawings from the National Archives. Too bad that the revision history is not available. With that we could determine exact dates of implementation of changes.



Sorry, for some reason I skipped over that part of your post.

I wonder if they would be able to give you that info if you asked for it?

It might be worth a try...

BEYU

"Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety."

- Benj. Franklin
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Jackp
Veteran Member



USA
1064 Posts

Posted - 07/07/2018 :  2:36:39 PM  Show Profile Send Jackp a Private Message  Reply with Quote
BEYU, I have attempted to navigate the National Archives searchable web site directory and have been unable to find anything relevant to carbine manufacture. If I were to find something, unless it has been digitized, I would have to personally visit the location where that document is stored. There are people who make a living doing this. I personally don't have the resources to take this any further than I already have. Other than the Nicolaus book I have only been able to find a few earlier drawings which have been redacted to remove names, dates and revision history. Here's an example of what I have found.

You must be logged in to see this link.

JackP
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BEYU
Advanced Member



USA
309 Posts

Posted - 07/07/2018 :  6:35:08 PM  Show Profile Send BEYU a Private Message  Reply with Quote
JackP, I understand.

I have been to the National Archives in College Park, Md. The people there, government employees all, act as though they are doing you a favor to let you be there.

Frequently, if you can even get them to give you a straight forward answer to a question, you are lucky.

I will never go back there. I have obtained enough info now that I can just order it from them for a relatively modest fee. BUT — you have to know in advance what you are looking for, and have an idea where it is.

You have likely done all you can.

BEYU

"Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety."

- Benj. Franklin
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Tuna
Moderator



3306 Posts

Posted - 08/01/2018 :  9:07:07 PM  Show Profile Send Tuna a Private Message  Reply with Quote
And they will not look for material in all of the storage areas for you UNLESS your a published author. I was surprised when I was told that years ago. Like a slap in the face.
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BEYU
Advanced Member



USA
309 Posts

Posted - 08/02/2018 :  09:55:08 AM  Show Profile Send BEYU a Private Message  Reply with Quote
quote:
Originally posted by Tuna

And they will not look for material in all of the storage areas for you UNLESS your a published author. I was surprised when I was told that years ago. Like a slap in the face.



Yeah — after all, who are WE to ask for anything? Just the people who pay them.

BEYU

"Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety."

- Benj. Franklin
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