IBM receiver with flat area
Printed From: The Carbine Collector's Club
Category: The Club
Forum Name: Club Requests and Member Submissions
Forum Description: Submissions, Spotters Reports, Documents, Sharp Eyes Dept.
URL: http://www.uscarbinecal30.com/forum/forum_posts.asp?TID=4629
Printed Date: Apr 19 2024 at 6:09pm
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Topic: IBM receiver with flat area
Posted By: PLN-TAP-7
Subject: IBM receiver with flat area
Date Posted: Apr 18 2020 at 2:58pm
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Hi, here is a picture of an IBM receiver with a flat area in front of the rear sight. This carbine (in the 3 million so January to March 1944 number) must have been through the French Army and is not as out of factory (M2 stock, rear sight, bayonet lug). Would someone know about the flat area? Has this specificity already been observed? It may only be a machining error...  |
Replies:
Posted By: New2brass
Date Posted: Apr 18 2020 at 3:58pm
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Good reporting! To the flat spot I have observed them on IBM. I would have to look if it was in a specific range. IBM only delivered for 9 months. they had only one serial number block 3,651,520 to 4,009,999. They did not use all their numbers. So tough to put it to a date even though some book estimate ranges. ------------- http://www.uscarbinecal30.com/forum/club-assistance-saginaw-receivers_topic4716.html" rel="nofollow - Club Survey Saginaw Receivers |
Posted By: Dave Tennent
Date Posted: Apr 18 2020 at 6:29pm
Here's another IBM receiver flat spot example.   ------------- Dave |
Posted By: carbinecanuck
Date Posted: Apr 18 2020 at 11:11pm
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Strange timing for this topic. Just looking at an IBM right now. Showing a similar flat spot. Serial range 366xxxx. I wanted to ask a question about the rear sight, but won't hijack this thread. Will start another for that. Here is a pic of the receiver for reference ....  ------------- Courage is fear holding on a minute longer. - GEORGE S. PATTON |
Posted By: PLN-TAP-7
Date Posted: Apr 19 2020 at 3:23am
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The first picture is IBM serial 3 821 XXX. So we have 3 6, 3 7 and 3 8 example.
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Posted By: carbinekid
Date Posted: Jun 09 2020 at 5:45pm
I just saw a Standard Products carbine with similar flat spots posted in the CMP forum. |
Posted By: thompal
Date Posted: Jun 09 2020 at 11:46pm
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Is there any significance to one flat area being behind the sight, and the other one in front of it? |
Posted By: Guests
Date Posted: Jun 10 2020 at 7:04am
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interesting. Of note is the fact that the flat area is behind the sight. Would it be that IBM receivers ' got it in front and SP at the back only?
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Posted By: kro1970
Date Posted: Jun 10 2020 at 10:47am
| I have Standard Products 1985XXX and it has the flat areas in front and behind the dovetail. |
Posted By: carbinekid
Date Posted: Jun 10 2020 at 10:55am
| The STD. Product receiver I shared does have flats on front and back. Sorry that I didn’t point that out. |
Posted By: New2brass
Date Posted: Jun 10 2020 at 11:51am
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The following is just a guess! They would "Gang" mill the receivers to the final profile. This would be an arbor with several profiled cutters would be sandwiched together to make the cut. The cutter in the middle may have left an odd profile when it got to the dovetail which was in excess of tolerances, or maybe it was done on separate passes and the arbor needed to get closer to the dovetail. Maybe at some point there was a variation of the forgings and the cut would be to great so they reduced the profile Again, just guesses! Notice how the flat area is cut perpendicular to the longitudinal cuts of the receiver @carbine kid, Pics?
------------- http://www.uscarbinecal30.com/forum/club-assistance-saginaw-receivers_topic4716.html" rel="nofollow - Club Survey Saginaw Receivers |
Posted By: choprboy
Date Posted: Jun 10 2020 at 10:30pm
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Putting my home-machinist hat on. The flat spots look to have been made on a horizontal mill with a straight wide milling cutter at a depth close to that of a finished profile. I would suspect that the machining steps to produce to top surface of the receiver would be to: 1) rough mill the top of the block with a straight cutter (making the top surface of the rear sight mount) 2) rough mill toward the rear site mount from either side with a straight cutter 3) finish mill toward the rear sight from either side with a concave cutter (to produce the convex top surface) If the stop point of the #2 roughing pass was set to close to the sight mount, it would cut below the finished profile, leaving a flat spot in the final product. |
Posted By: sfal7418
Date Posted: Jun 11 2020 at 5:55am
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interesting study...my Standard 2003520 has no milled spot Al
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Posted By: foxhole49
Date Posted: Jun 21 2020 at 12:48am
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Just checked. No flat spot, front or rear, on IBM 37317xx, or on Underwood, 61272xx. Seems taht the flat spots are at random. Must be a reason for them. |
Posted By: hunterman
Date Posted: Jun 21 2020 at 9:37am
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For those keeping score, there is an IBM with the flat spot on the receiver on GunBroker now. Serial # 3,654,3XX. |
Posted By: tenOCEE
Date Posted: Jun 21 2020 at 6:56pm
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The 3.71 I have has at least one flat in front of the dove tail. There's another one here I know but not sure what the serial is. ------------- My sig: Seen an IP or S'G'? Add it to my registry. We'll check consecutives. https://grandrapids.wufoo.com/forms/zzlnt0519k86xs/" rel="nofollow - https://grandrapids.wufoo.com/forms/zzlnt0519k86xs/ |
Posted By: 03manV
Date Posted: Jun 21 2020 at 11:13pm
Yes, the reason is in the rough and finish milling of the receiver contour, as mentioned above. The flat is cosmetic and a result of forging voids or milling variation. JMHO.  ------------- Don |
foxhole49 wrote:Posted By: painter777
Date Posted: Jun 22 2020 at 4:01pm
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IBM Here 3,849,505 with Flat Spot on the front. Can't see the backside because of Type II rear sight. CH-P777 ------------- Living Free because of those that serve..... |
Posted By: painter777
Date Posted: Jun 22 2020 at 6:02pm
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Also IBM 3,857,1xx with Flat Spot on the front. (Not Mine) Like the 3,859,505 posted above, both have Round Bolt with the X. Flat spots on both nearly identical. fwiw CH-P77  ------------- Living Free because of those that serve..... |