Hardness Dimples on June 1942 manufactured Inland Receivers

[Hammer]

Painter777's favorite Old Threads showed a pic of Inland 1205 and I noticed it also had a round dimple impression on its left side receiver wall as I had seen on other June 1942 made Inland receivers. I posted about this on the Carbine Collectors Club a few months back when I found this round dimple impression on the left side of my Inland 270 Receiver and was curious what it was so I started asking around and looking at 3 and 4 digit Inlands and found this same impression on others that were made in June thru early August 1942. I saw these dimples (as I call them) on all of the 3 digit receivers pics I could find and on most of the 1000 series receivers, and on some of the 2000 series, but only on one in the 3000 series and it was SN 3546.

This round dimple is believed to be a hardness test. Its not the ping punch type markings seen on parts which are from a Rockwell hardness test. This larger round impression is believed to possibly be a Brinell Hardness test mark, which can measure the lower end of the hardness scale. Inland was doing this on its Receivers in its first month of production it seems and continued it sporadically into July and early August.

Some of these earliest receivers have just one dimple and others have up to 4 on them. They are on the different areas of only the the left side wall of the receiver.

Here's some pics from 3 digit and 1000, 2000, low-mid 3000 SN's.

Attachment 121604Attachment 121605Attachment 121606Attachment 121607

Information

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[Hammer]

Attachment 121609

[eb in oregon]

Brinell testing does leave a dimple. If there is more than one dimple that suggests they were tested more than once. Why? Material problems, oven problems, other problems. But the rifle is in hand so it passed the first time, or maybe after a few tries. It passed eventually. And once the process is verified only spot checking is necessary.

[Flying10uk]

It's interesting to see evidence of the quality control in use at the time of manufacture. The dimples show that the receiver was thoroughly tested for the correct hardness, at time of manufacture, and as it passed and as it wasn't "destructive testing" the tested receiver was despatched for assembly with the all of the other receivers that hadn't been tested.

[jimb16]

Perhaps multiple dimples are from checking the calibration of test equipment on a carbine of "known" hardness. Just speculation on my part, but it is plausible.

[Hammer]

Attachment 121615

You can see four indentions on this Serial Number 34X receiver - two on the left front, one in the middle, and a larger one in the right rear. My SN 270 only has the one larger indention in the middle of the receiver's wall.

[DaveHH]

This is really a nice look into Inland's introduction into gun manufacture. They were a results oriented company for sure with an ego and reputation to uphold. At this time they were apparently in the do it right stage. Later on they were petitioning Ordnance to use barrels that were not so great but would work. The pressure to produce must have been incredibly heavy.

[eb in oregon]

Attachment 121615

You can see four indentions on this Serial Number 34X receiver - two on the left front, one in the middle, and a larger one in the right rear. My SN 270 only has the one larger indention in the middle of the receiver's wall.

Checking multiple locations is common to insure the heat treating process is consistent. Again, once verified only spot checking is required. As manufacture gears up multiple tests are usually required. As it becomes apparent the process is consistent checking becomes more a random thing rather than a "check every one" thing. Time is money. Or a delay in getting guns to the troops. But that's merely an opinion.

[Hammer]

I can only imagine the pressure Inland must have been under to produce the "new" M1 Carbine as quickly and correctly as possible because the 1st Infantry Division was shipping out to England in early August in order to make its Combat Landing in North Africa just a few months later. Inland had to try to make close to 7000 or more Carbines in just 3 months and these first production run carbines just Could Not Fail...

Amazing American Ingenuity, Resolve, and Patriotism :-)

[ssgross]

had not there been a discussion of hardness testing, I would have guessed maybe the mark was a witness or index mark showing correct alignment in whatever jig was used in the milling processes.