Unknown Magazine Conversion - Or - Just When You Thought You Knew Your M3 Grease Gun Variants
By Byron D. Zappandecker III *

During a recent visit to a forensic science service establishment in the United Kingdom, a hitherto unknown variant of the M3 submachine gun (well, unknown to this author) was identified. Perusing the racks of reference firearms, one’s eye was cast over the SMG collection of familiar Stens, MP40s, Uzis and the like. More of the same for the small number of M3 and M3A1 submachine guns or ‘Grease Guns’ in popular jargon. But wait! Something catches the eye; one of the M3’s is fitted with a non-standard magazine? The gun is hastily retrieved for examination. First thoughts consider the likelihood of conversion by an enthusiast who maybe had lost the original magazine and had fitted another to make the gun complete or, is it perhaps the result of criminal activity?

A detailed examination showed that the gun appears to be an original M3 model. Identifying markings on the left-hand side of the magazine housing again appear to be original and the gun has an early serial number of 51, placing it in the earliest of production runs. The calibre is confirmed as the original .45 ACP. The gun appears to be all original parts, excepting the magazine, which while not in the best of condition appears to be of possibly Austrian or Italian origin. However on examining the magazine well, a sheet-metal insert is noted. The metal insert is held in place by the magazine release catch located on the right-hand side of the magazine well. Disassembling the magazine release catch unit and removing the actual component that holds the magazine in place, allows the insert to be removed.

The examination of the magazine insert shows that it is well made and apparently purpose-built. The is no evidence of a piece of sheet-metal being cut to size with ‘tin-snips’ or the skills of panel-beater being used to form the insert around a home-made mandrel.

To ensure that the conversion related only to the calibre and not the cartridge, an inert .45 ACP round was chambered in the breech to confirm calibre of gun; likewise the breech-block face was checked to confirm original calibre. (The well-trained observer will note that the ‘guide rod retaining clip’ is absent.) The marking of the breech block in a position visible with the ejection port cover opened (for loading) tenuously suggests that whatever military or para-military organization were armed with this conversion, also perhaps had other calibre weapons of the generic M3 in service.

The magazine as commented on above appears to have similarities to a Beretta design. The length of the magazine from front to rear is more than adequate to accommodate the length of a .45 ACP round, suggesting perhaps that this magazine is intended to fire a cartridge with a greater overall length than the ubiquitous 9 x 19 mm or the .45 ACP cartridges. The change from a double-column, single-position feed configuration of the original M3 magazine (not its best point) to a double-column, twin-position feed magazine may well be one of default, arising out of the use of a pre-existing magazine. The magazine while not in the best of condition appears to be the correct one for use with the sheet-metal insert, with insertion and locking being positive, with magazine release/removal using the magazine catch being accomplished with ease.

The provenance of this gun appears to be lost in the depths of time. The conversion does not appear to be an illegal conversion, as the insert gives the impression of being a professional rather than amateur conversion. So the question to be asked is – does anybody out there among the professional and gun collecting communities have any further information on the reasons for this conversion, which simply allows the use of a different magazine than that issued. Reports of shortages of original M3 magazines, which would perhaps explain away the magazine conversion, do not, for this author, immediately spring to mind. So again, why a magazine conversion? Anybody know?

(*) – Byron D Zappandecker III is a pseudonym for the last Custodian of the MOD Pattern Room, small arms collection who wishes to remain anonymous.

This article first appeared in Small Arms Review SAW (February 2013)
and was posted online on December 21, 2012


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