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Carbine Parts Drawing Questions

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jackp1028 View Drop Down
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Post Options Post Options   Thanks (4) Thanks(4)   Quote jackp1028 Quote  Post ReplyReply Direct Link To This Post Topic: Carbine Parts Drawing Questions
    Posted: Feb 10 2019 at 9:07pm
Carbine Drawing Questions



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, disposition 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 for purchase on his web site. This book contains the latest complete detailed drawings of all the carbine parts along with related assembly drawings. These are Ordnance drawings 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 can be found 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” minimum from the centerline of bore or 1.115” minimum from the bottom of sight (Type 1 and 2 only).

2)     Is the receiver dovetail tapered from left to right? We are always told to install the rear sight from right to left and to remove it from left to right. No, the dovetail is not tapered. The primary reason to remove the sight from left to right is to avoid possible interference with windage knob.   However, it should be noted that installing or removing the sight from the left side may cause damage if the dovetail has suffered deformation resulting from the previous assembly of a tight-fitting sight from the right side as instructed in the Ordnance drawing and subsequent staking instructed in the TM’s and not from a pre-existing “taper”.

Note:  Subsequent investigation has found a reference to the dovetail being “tapered” in the 1947 issue of TM9-1276 page 61, para. 46b .  Also noted was a reference to the “S” stamped on the left ear as meaning the “small” side of the sight. 
 
 
These references were not found in the later 1953 issue of TM9-1276 (link below).
 
 
As already suggested, the rear sight should be removed from left to right to prevent damage to the sight or receiver dovetail.

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

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 a 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 the front sight.

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

8)     What is the width and height of the rear tab on the operating slide? Often suspected of causing the slide to unexpectedly disengage from the receiver.   .090” -.003 by .240” +-.002 for Type 1-5 (M1), .090” -.003 by .243” -.006 For Type 6 (M2)

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. Later post-war RIA recoil plate measures .438).

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

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

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

14)     What is the carbine barrel made of?   Can a cracked gas cylinder be successfully welded?   Steel, Mil S-11595 Chrome-Moly-Vanadium or 4150 re-sulpherized. This may have applied to later barrels only. It was reported that early barrels were made of WD 1350 re-sulpherized steel and should not be welded.

15)    I need to retap damaged threads on the gas cylinder.  Does anyone know the diameter and pitch of the threads?   The original Ordnance specification is "1/2-32 NS-3".  However, this may be an obsolete thread standard.  The modern equivalent is a .500"-32 TPI plug tap per Kuhnhausen’s Shop Manual.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote blackfish Quote  Post ReplyReply Direct Link To This Post Posted: Feb 11 2019 at 2:52am
Originally posted by jackp1028 jackp1028 wrote:

2)     Is the receiver dovetail tapered from left to right? We are always told to install the rear sight from right to left and to remove it from left to right. No, the dovetail is not tapered. The primary reason to remove the sight from left to right is to avoid possible interference with windage knob.   However, it should be noted that installing or removing the sight from the left side may cause damage if the dovetail has suffered deformation resulting from the previous assembly of a tight fitting sight from the right side as instructed in the Ordnance drawing and subsequent staking instructed in the TM’s and not from a pre-existing “taper”.


I believe this is incorrect. If you examine the drawings carefully, you will find that the left side of the receiver dovetail is a bit narrower (0.006" IIRC) than the right side.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jackp1028 Quote  Post ReplyReply Direct Link To This Post Posted: Feb 11 2019 at 12:49pm
@Blackfish, thank you for your response. I knew this could be a controversial subject. The Ordnance drawing does show an angle of 30 minutes for the dovetails on both the receiver and rear sight. Such an angle would result in a "taper" of .0055" across the receiver as you mentioned. However, if interpreted in this manner, the dovetail would be wider on the left side of the receiver, not the right. Here's a clip from the Ordnance drawing:



It is believed that this angle was given as a tolerance, not a required dimension. It is meant to require that the sides would be parallel within half a degree and square with the center-line of the receiver within a quarter of a degree.

The side view also below shows the angle of the dovetail as being 30 degrees with a tolerance of 15 minutes. Again, the 15 minutes is a tolerance not a required dimension.



I have attempted to measure several dovetails and found it difficult to get a consistent reading due to the deformation of the receiver caused by the interference fit of the sight and subsequent staking. Perhaps this deformation results in a perceived "taper". Also, it has been suggested that an assembly instruction may have existed that permitted "filing" the opening to the dovetail to facilitate assembly or "pressing" the dovetail down to tighten the fit. This may have also resulted in a perceived "taper". The image below shows the method used to measure the dovetail:



The process used to machine the carbine dovetail (as described in War Baby!, pg. 72, operation #47) does not lend itself to achieving such an angle without multiple setup changes and multiple operations, which would be difficult and costly. It is described as a single operation, at least by Winchester.

Finally, I have searched for any description of a dovetail machining process that would intentionally result in a taper and, so far, no luck.

Any information that you might have on the topic would be greatly appreciated.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote blackfish Quote  Post ReplyReply Direct Link To This Post Posted: Feb 11 2019 at 4:42pm
Well, you could be right about that angular spec and I stand corrected. I'm not a machinist and interpretted it as something other than a tolerance. I don't have any of my reference materials with me so I can't "research" this further from here.

What does the S mean on the left side of the leaf sights, with no windage knobs to get in the way?

What does Fulton Armory do? Their commercial receivers are "supposed to be" to USGI spec and they use real machinists. Does their receiver dovetail have a manufactured "taper"??? While I'm quite sure they won't share their drawings and CAD models, I feel fairly confident that they could and would tell you whether their sight dovetail is tapered, or not.

Be interesting for sure.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote jackp1028 Quote  Post ReplyReply Direct Link To This Post Posted: Feb 11 2019 at 5:10pm
@Blackfish, I don't have any drawings of the flip sight. So I have no authoritative documentation to support this reply. However I believe I am correct in saying that the "S" on the flip sight base stands for "Sinister" which is Latin for "on the left side" ("Dexter" is for "on the right side"). In the past, being left handed was considered evil in many cultures, thus the negative present day definition.

It's real easy to get a flip sight on backwards. We see it all the time in supposedly "original" carbines. Some say the aperture was put in the base backwards, some say that the whole thing is on backwards. It varies. As you know, there's a discussion going on right now about this very topic in the General Discussion forum.

http://www.uscarbinecal30.com/forum/backward-flip-sights_topic3859.html#26963
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Post Options Post Options   Thanks (0) Thanks(0)   Quote m1a1fan Quote  Post ReplyReply Direct Link To This Post Posted: Jun 14 2020 at 12:57pm
Really struggling to get an accurate measurement of the right/left side dovetail opening as I'm not a machinist or engineer.

I've tried dial calipers and then don't seem like the right tool for the job since they won't bottom out due to the design. Also, I really don't want to accidentally mar the metal. I've also tried firm-joint calipers by they too don't reach the bottom of the dovetail.

Ideas are welcome on how to get an accurate measurement as I'm assuming the measurement should be taken at the bottom of the dovetail. So far, the most consistent tool measuring has been a ruler, but the bottom of the dovetail is slightly concave.

Also wondering if there was an armorer's tool for such a measurement?

Thanks!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote blackfish Quote  Post ReplyReply Direct Link To This Post Posted: Jun 14 2020 at 1:23pm
Just call Fulton and ask. Tell them BLACKFISH sent you. They make the dovetails so they know HOW they make them.

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Post Options Post Options   Thanks (1) Thanks(1)   Quote New2brass Quote  Post ReplyReply Direct Link To This Post Posted: Jun 14 2020 at 2:14pm
Originally posted by jackp1028 jackp1028 wrote:


Note:  Subsequent investigation has found a reference to the dovetail being “tapered” in the 1947 issue of TM9-1276 page 61, para. 46b .  Also noted was a reference to the “S” stamped on the left ear as meaning the “small” side of the sight.

As a subsequent followup to the note added to the top post and the meaning of the "S"

It can also be found in
TM 9-1276 (1943) page 45 states the dovetail tapers to the left. the small end (of the sight) is stamped "S"

 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote painter777 Quote  Post ReplyReply Direct Link To This Post Posted: Jun 15 2020 at 3:28pm
Jack,
I see that David Anthony @ Matrix sells a gas block thread kit with jig and tap.
Currently out of stock but I know he takes back orders or will email you when back in stock.
He's a good guy.... You might be able to contact him for the tap size.

Link:

Good Luck,
Ch-P777

ETA: Sorry I overlooked this part:
The modern equivalent is a .500"-32 TPI plug tap per Kuhnhausen’s Shop Manual.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote jackp1028 Quote  Post ReplyReply Direct Link To This Post Posted: Jun 15 2020 at 5:57pm
@Charlie, Amazon has the same tap for $16.99.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SeaCay Quote  Post ReplyReply Direct Link To This Post Posted: Aug 19 2020 at 1:43pm
JackP, thanks for this information, it will be helful to me.  A related question I had is if there is a single source/topic somewhere within this forum (or elsewhere) that might have a step-by-step inspection type checklist for all or most of the parts?  

As I breakdown and clean up everything, I was hoping there might be something that says what to look for visually and/or dimensionally to determine usability.  i.e. my bolt looks worn but is it "to" worn? or just the original finish worn away...does the TM have all of that info in it?

Thanks!
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Post Options Post Options   Thanks (2) Thanks(2)   Quote jackp1028 Quote  Post ReplyReply Direct Link To This Post Posted: Aug 19 2020 at 2:33pm
In addition to the TM's, I have found the book "The U.S. .30 Caliber Gas Operated Carbines A Shop Manual" by Jerry Kuhnhausen to be the most complete single technical resource for determining visual and/or dimensional usability. This book contains detailed written descriptions of what to look for as well as photo examples and related dimension drawings. It utilizes illustrations that are copied from the original Ordnance drawings that were used to fabricate the parts.

One point I would like to make. Just because you have the detailed dimensions of a part does not mean you will be able to easily measure the part in a way to verify many of those dimensions. These parts were fabricated and inspected using fixtures and gauges that probably no longer exist. Without such fixtures and gauges you will not be able to confirm many of the critical dimensions. For example, try to verify head space without a head space measuring gauge.       
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Post Options Post Options   Thanks (0) Thanks(0)   Quote painter777 Quote  Post ReplyReply Direct Link To This Post Posted: Dec 24 2020 at 6:17pm
JP,
Sure glad you put this together it comes in handy often.

I recently came across this Thread tap while on Amazon. Reading the reviews looks as though it worked well for most.
Some mentioned though it wasn't described as a being a N3, but did receive a N3.
1/2-32 TPI HS Special Thread Tap-Bottoming.


I've read where others used a similar one but it was too long for a barreled receiver.
All have to keep in mind there is less than ~3 --1/2" to work in.

FWIW,
Ch-P777

 

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Post Options Post Options   Thanks (1) Thanks(1)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Dec 24 2020 at 6:34pm
Plus 1 on the difficulty of measuring certain components. I find it helpful to pick points that I can measure and compare those points between known good components and those that are suspect. It seems impossible to measure some dimensional values posted on drawings.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote GotSnlB28 Quote  Post ReplyReply Direct Link To This Post Posted: Dec 24 2020 at 6:57pm
Originally posted by painter777 painter777 wrote:

JP,
Sure glad you put this together it comes in handy often.

I recently came across this Thread tap while on Amazon. Reading the reviews looks as though it worked well for most.
Some mentioned though it wasn't described as a being a N3, but did receive a N3.
1/2-32 TPI HS Special Thread Tap-Bottoming.


I've read where others used a similar one but it was too long for a barreled receiver.
All have to keep in mind there is less than ~3 --1/2" to work in.

FWIW,
Ch-P777

<h1 id="title" ="a-size-large a-spacing-none" style="-sizing: border-; padding: 0px; margin-right: 0px; margin-left: 0px; text-rendering: optimizelegibility; font-weight: 400; color: rgb15, 17, 17; font-family: "Amazon Ember", Arial, sans-serif; font-size: 24px !imant; line-height: 32px !imant;"> </h1>


I bought this very tap off Amazon and it worked perfectly. A used barrel I bought had the first couple threads slightly damaged from the old staking when the piston nut was removed by a previous owner. Good as new now. And before I bought I checked this reference too, very handy!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 320th INF Quote  Post ReplyReply Direct Link To This Post Posted: Jan 19 2022 at 4:56pm
Guys,

I picked up the tap mentioned above by painter777 for the gas piston nut on an M1 Carbine from Amazon. I'm in need of some good advise as I am not familiar with the tap markings I received. The tap I received is marked;         

                                     HANITA HS  GT
                                       1/2" 32 - UN...
                                            S-4

The invoice states 1/2-32 H3 BOTTOM TAP.  Part number 12123232.  Is this the correct tap for the gas piston?  I'm not touching it until I get smarter.. That may take a while.....

Thanks for any help, or advise,

Tom
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jackp1028 Quote  Post ReplyReply Direct Link To This Post Posted: Jan 19 2022 at 6:31pm
It is the correct tap.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 320th INF Quote  Post ReplyReply Direct Link To This Post Posted: Jan 19 2022 at 7:02pm
Jackp,

Thanks for the quick reply.  I didn't want to assume anything.

Thanks again,

Tom
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 320th INF Quote  Post ReplyReply Direct Link To This Post Posted: Jan 19 2022 at 7:08pm
Guys,

FYI, I received an email from the original Amazon vendor and he stated, "yes it is' the correct tap.

From the below company;

North Bay Cutting Tools
1325 Ross Street
Suite F
Petaluma, CA 94954
707-773-2240

Thanks,

Tom
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