Any information on British modifed US M3 SMG magazine catch

[Vincent]

It looks like a sling attachment.

IIRC, Frank Iannamico covers it in his book “The U.S. M3-3A1: Submachine Gun: The "Grease Gun".” Maybe he will chime in.

The original M3 catch was prone to inadvertent dropping of the magazine. A cover was added to correct the problem.

Information

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[RCS]

Vincent, I found information on a machnegun website, Frank Iannamico is on this website too. They call it the "British horseshoe bar" and said it was a British modification. When I was an armorer
in the US Army, I saw only the M3 SMG and none were modified with this bar welded on the receiver.

[browningautorifle]

The original M3 catch was prone to inadvertent dropping of the magazine.

That first statement is correct...

"British horseshoe bar"

And that sounds about right. It wasn't a standard US mod. The lower one was.