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The Saginaw Streering Gear MG-42

This is a discussion on The Saginaw Streering Gear MG-42 within the Full Automatics forums, part of the Gun Forum category; In 1942 a captured MG-42 was examined by the US Army and generated great interest and the possibility of adapting it for use with the ...


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Old May 7th, 2020, 06:30 PM   #1
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The Saginaw Streering Gear MG-42

In 1942 a captured MG-42 was examined by the US Army and generated great interest and the possibility of adapting it for use with the Army was considered. Accordingly, a contract with the Sagniaw Streering Gear Division of General Motors for the construction of two machine guns following the lines of the German weapon, but incorporating modifications to suit US Army requirements. These two guns were designated Light Machine Gun, Caliber .30, T24, and were delivered to Aberdeen Proving Ground (APG) on 6 January 1944.

Many people have written about the T24, much of their information is misleading, or just wrong. Forgotten Weapons did a piece on these a while back, I am surprised/disappointed that Ian didn't actually do more research such just reading the report he obviously has a copy of, or just look closely at the pictures, before he made his little video. The first major things is he states that they were send to, and tested by Springfield, but the front cover of the report plainly states in big bold letters "Aberdeen Proving Ground".

Much has been made about Saginaw's engineering department's ability (or lack of) to design a weapon due to the rather sad attempt with the bipod. The BAR bipod explained in the report - due to the short time allowed for engineering and construction (less than a year), copying the bipod was low priority. The bipod and sights were not shipped with the machine gun. It order to test the weapon a bipod was required, so at Aberdeen, a BAR bipod was fitted. The same was true for the sights, and the tripod adapter. This is plainly stated in the report. The unfortunate placement of the tripod adapter comes into play later.

The T24s were not build on MG-42 receivers, if they were, they would have had MG-42 sights and bipods already fitted. Further just reading the weights and dimensions tell you these are quite different receivers. Similarly, looking at the pictures of the T24 you can see that these are not MG-42 receivers. 1) The mounting support for finger that holds the flash hider/muzzle booster indexed and is the mount for the front sight is an integral part of the receiver stamping on the MG-42, on the T24 these are two different parts and are clearly brazed on. There are also big differences in where the bipod would mount, on the MG-42 it is part of the stamping, on the T24 it is a separate machined piece brazed on. There are many clues that these were not converted MG-42 receivers, some of the lightening holes are missing from the bottom of the T24, and there are more holes on the top.

I do not know where people got the idea that the ejection port was too small. Even if they had made the receiver with an ejection port sized to the MG-42, it still would have been big enough to eject a spent .30-06 case. True, a 7.9 Mauser case is 6mm shorter than a .30-06 case, but the MG-42 could eject a fully loaded 7.9mm cartridge which is 82mm long, so plenty on length for a spent .30-06. But, these were new produced receivers.

The guns were a disappointment, that much is true.

Both guns were to be subjected to an several tests, accuracy, operation with low pressure rounds (lot avg 38,000 psi), operation with high pressure rounds (Lot avg 55,000 psi). Unfortunately, during the very first test, just a 100 round belt to get the feel of the guns, gun #2 refused to eject practically every round. Examination of #2 revealed the causes to be: the right bolt guide rib was improperly shaped* and retracting handle was galling its track, other problems were the feed cover wouldn't stay closed, and the headspace was 1.955, well over the limit. Gun #2 was set aside and all further testing was done with gun #1.

During the accuracy test, 366 rounds were fired with 18 failures to eject, 2 failures to feed and one failure to fire.

During the general functioning test, 300 rounds were fired with 17 short recoils, 2 failures to feed, and one ruptured case.

During the Low-High pressure test, 50 rounds of low pressure (lot avg 38,000 psi) and high pressure (lot avg 55,000 psi) ammunition was fired.

Low pressure - 2 failures to feed (short recoil), and 1 failure to eject.

High pressure - satisfactory

A total of 1583 rounds were fired through gun #1 during the endurance test,out of a planned 10,000, with 51 recorded malfunctions:

Rounds 1-200:
8 failures to eject (short recoil)

Rounds 201-300: (booster with .600" diameter orifice)
6 failures to eject (short recoil)

Rounds 301-365: (booster with .425" diameter orifice)(cyclic rate - 725 rpm)
satisfactory

Rounds 366-415: (booster with .425" diameter orifice)(cyclic rate - 725 rpm)
1 failure to feed
1 failure to eject

Rounds 416-465: (booster with .425" diameter orifice)(cyclic rate - 725 rpm)
satisfactory

Rounds 466 to 495: (booster with .460" diameter orifice)
2 failures to eject (case caught between retracting handle and bolt)

Rounds 496 to 525: (booster with .600" diameter orifice)(cyclic rate - 610 rpm)
1 failure to eject (short recoil)

Rounds 526 to 575: (booster with .600" diameter orifice)(cyclic rate - 610 rpm)
satisfactory

Rounds 576 to 625:
3 failures to eject
1 ruptured case
1 failure to feed (stubbed round)

Rounds 626 to 675:
1 failure to feed (short recoil)
3 failures to eject (head of case caught between bolt face and ejection port)

Rounds 676 to 725: (buffer advanced)
1 failure to eject
1 ruptured case

Rounds 726 to 733: (bolt from gun #2 installed)
5 failures to eject

Rounds 734 to 783: (bolt from gun #1 re-installed, barrel #5 installed headspace 1.941")
satisfactory

Rounds 784 to 833: (bolt from gun #2 installed)
2 failures to eject (retracting handle being hit by barrel recoiling, end relieved)

Rounds 834 to 883: (bolt from gun #2 installed)
satisfactory

Rounds 884 to 933:
1 failure to feed (stubbed on bottom of barrel face)

Rounds 934 to 983: (bullet ramp bent, replaced with ramp from gun #2)
1 failure to feed (stubbed on bottom of barrel face)

Rounds 984 to 1033:
1 failure to feed (not pushed from belt)
2 failures to eject

Rounds 1034 to 1083:
1 failure to feed (stubbed on bottom of barrel face)

Rounds 1084 to 1133:
1 failure to feed (stubbed on bottom of barrel face)
1 failure to feed (not pushed from belt)
1 failure to eject (case caught between retracting handle and bolt)

Rounds 1134 to 1283:
1 failure to feed (stubbed on top of barrel face)
2 failures to eject

Rounds 1284 to 1333: (cut down MG-42 buffer spring installed)
2 failures to feed

Rounds 1334 to 1383: (bullet ramp broke attempting to correct feed failures, replace with MG-42 ramp)
satisfactory

Rounds 1384 to 1433
1 failure to eject

Rounds 1434 to 1483: (retracting handle removed)
satisfactory

Rounds 1484 to 1533:
1 failure to eject

Rounds 1534 to 1583:
satisfactory

At this point, the officer in charge suspended testing and declared that more developmental work would be required before testing could resume. The Belt

lift was only 60 rounds, this is indicative of a weak action, normally a machine gun will pull a minimum of 150 rounds. The M60 and M240 have a belt

pull of 200 rounds.

So, why did these fail so miserably?

The report doesn't state, as Aberdeen is a test facility, they rarely do any diagnostic on why your piece of equipment fails to work. But, the report gives some big hints. The most important hint is the cyclic rate of the MG-42 tested was 1200 rpm. The T24 was supposed to work at 600 rpm, half of the original design. That is a major change in the design. As an thought experiment, do you think adding a little weight to an M14 operating rod and changing the spring would result in an M14 that could reliably shoot at 375 rpm?

A major part of the problem is the way an MG-42 works (and all of the German WW2 high rate machine guns for the most part), in that the mainspring actually doesn't do much, other that close the bolt for the first round. After the first round, the bolt just bounces off the buffer assembly, and retains most of it's energy. In most US designs the buffer is a relatively soft spring that absorbs energy. To keep the cyclic rate down the the initial bolt velocity had to be kept low, which means it never had as much energy as the original design to begin with, so you see failures to feed. You see a lot of failures to eject attributed to short recoil. And it worked better with the high pressure rounds and when the cyclic rate was raised to 725 rpm.

And, one other thing that has a lot to do with the failures to eject is the trigger housing is now immediately behind the ejection port (because the ejection port is longer!), and now the added knuckle for the US T&E device at the front of the
trigger guard is perfectly placed to ensure that ejected cases can bounce off it and spin right back into the ejection port.

Why no further work? Speculation on my part, but I think the powers that were saw the simple fact that the MG-42 works because it shoots at a very high cyclic rate. And, the Army at the time didn't want a very high cyclic rate machine gun. So, the project was shelved.
___________________________
*This is part of the receiver, so why would an MG-42 that was used in combat, have improperly shaped parts that prevented operation? It wouldn't, these were new manufactured receivers.

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Old May 7th, 2020, 08:05 PM   #2
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Interesting. I was unfamiliar with this effort at SG. They were the major producer of the 1919A4, and the only producer of the 1919A6, during the war. Of course they also manufactured M1 Carbines and other stuff as well. Their quality of manufacture was highly regarded on the Brownings, and they were the only maker where the breech lock cam was allowed to be staked tight instead of left floating. That was an allowance for the durability of SG receiver bottom plates. Cam float reduced the pounding on the plate.

Saginaw also cut the cost of 1919 manufacture by 90% over the course of the war, primarily by developing their ArmaSteel cast components, which proved equal or superior to the milled equivalents. The truly amazing part is that Saginaw found, at the end of production in 1945, that they had not used $213,000,000 which they had been paid. There was that much in cost savings left over. That's $213 million 1945 dollars. They reimbursed the U.S. government every penny. Show me a company that would do that today!

Interesting about the BAR bipods. Both the BAR 1918A2 and the 1919A6 used the same bipod legs, though with a different head to mount to, of course. Saginaw certainly would have had plenty of those legs, being the sole A6 producer. Not surprising they would have adapted that out of expediency to the T24.

Also worth noting that Saginaw was given little time to develop that 1919A6. They only began A4 gun production in the spring of 1941. Not sure when the A6 project began, but the first guns were issued about mid 1943. No one has ever claimed that the 1919A6 was anything but a clumsy, expedient attempt to make a more portable LMG out of the A4.

Early A6s had no booster, and were intended to allow barrel replacement from the front. But in an interesting parallel to your example of the T24 failing in the belt lift requirements, so too did the early A6. Hence, a redesign of the jacket, and a new barrel bearing/bipod mount with a clip-retained booster was introduced. Outside of photos and the Ord Dept. drawings, I've never seen any surviving example of the A6 as first produced. Probably all got upgraded and old parts scrapped.

Just for fun, here is the most interesting marking I've seen on an MG42 type. It's actually a 1970s vintage MG3, but it got over here and a very interesting registration marking was applied. Rather amusing, I think.
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Last edited by Lucky#13; May 7th, 2020 at 08:38 PM. Reason: Minor clarification added
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Old May 8th, 2020, 05:58 AM   #3
Lifer
 
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Hi,
LOL!

Soooo...We took a German Machine Gun, known for it's deadly reliability and considered by many (even today) as the greatest light MG ever made...

And showed the Germans how to screw it up!

Sounds about right!
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Old May 8th, 2020, 06:24 PM   #4
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The most interesting story I know concerning the MG-42 involved Sam Cummings. It seems after the war he bought all the captured MG-42s from the US and British armies at scrap metal prices, and put them in a warehouse. Then 10 years later, he sold them all back to the Germans for the Bundeswehr.

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