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Identifing Caliber .30 BMG Bottom Plates by kkkriverrats The bottom plate that all of are used to seeing with the 8 rivet flange to attach the side plates to the bottom plate and the integral T&E bracket did not always exist. How it came into being is a long, and we think an interesting story. First a little background. In 1925 the Ordnance Department changed model designations by dropping the “Model of” and substituting the upper case letter “M“. In this way the Model of 1917 became M1917. For the sake of clarity this paper will refer to all weapons by the post 1925 designation. Sometime in the middle 1930’s Ordnance stopped using the year in the identification of weapons i.e. it’s the “ U. S. Rifle, Caliber .30 M1” the famous Garand, not U.S. Rifle Caliber .30, M1936 it’s year of adoption, but Ordnance kept the original identification of existing weapons. From prior to WWI until about June 1, 1931 all M1917 drawings were numbered in the Class and Division naming convention. Machine guns were a Class 51 Major Item and the 1917 was numbered 10. Drawings were numbered sequentially starting with 1 which was the Assembly drawing showing views of the entire weapon.. Often, in the Class and Division system of identifying drawings, more than one part was shown on a sheet so a letter was added to the sheet number to denote which detail on that sheet was the part in question. The bottom plate appeared on sheet 10 detail C. The “Piece Mark” is the pre late 1943 term that Ordnance used to indicate how the part was numbered and in some cases how it was marked. The original M1917 bottom plate was assigned a Piece Mark of 10C. Not every part had a piece mark imprinted on it, some were just too small and as a matter of secrecy during WWI, none of John Moses Browning’s patents for the M1917 were filed until after the armistice on November 11, 1918, as after filing, the patents become public record. Original WWI parts were usually marked as to the manufacturer, but not necessarily with a piece mark to identify the part. Original production M1917 machine guns had a bottom plate that slipped into dovetail grooves machined into the side plates, and was both peened into place and held in position by the back plate. Farther on in this discussion you will find out the significance of peening of the side plates. As previously noted, this bottom plate was shown on drawing 51-10-10C. In 1922 Ordnance implemented a change in the way that drawings were numbered. Standard sizes were mandated and identified by the letters A thru E with A being the smallest and E being the largest. All of Ordnance’s drawings were redrawn on the new size medium and renumbered starting with 1 for each letter size. In addition only one part was shown on each drawing. During the interwar period which included the Great Depression, drawings were slow to be converted to the letter size format due to a lack of funds. In the case of the M1917 bottom plate, it wasn’t converted until June 1, 1931, when it became C8464. When the M1917 was introduced into combat late in WWI, reports of failures of the bottom plate dovetails, side plate grooves, broken cam blocks, cam block screws, and bulging side plates began to filter back from the front. WWI ended before anything could be done about this problem. Post war tests concluded that a reinforcing stirrup could be retrofitted to existing weapons to solve the immediate problem. This stirrup was about 2 ˝ inches long with an approximately 1” flange on each side with a hole in the bottom to accommodate cam block screw. It was riveted to the side plate with 2 rivets on each side. Starting in 1920 about 25,000 reinforcing stirrups were manufactured and installation of the stirrups was begun at the Springfield Armory where about 10,000 weapons were retrofitted thru 1926. Other ordnance facilities installed the stirrups both on a repair and return basis and inspection and refurbishing prior to storage operations. All quiet on the bottom plate front, sort of. In 1922 an Ordnance officer stationed at Springfield Armory, one Capt. Walter T. Gorton, designed and patented a new style bottom plate which included an 8 hole riveting flange and an integral T&E bracket that eventually became the bottom plate we are all familiar with. Since Capt. Gorton was an Army officer, his patent was assigned, without compensation, to the United States Government. Meanwhile, the Cavalry arm of the Army had been searching high and low for some sort of light weight automatic weapon for pack mounting. They briefly thought that that a modified BAR, the very short lived M1922, might be just the ticket, but later thought better of it. Since nothing seemed to be forthcoming from Ordnance, in 1930 they took the bull by the horns, acquired a 1919 tank gun and modified it for Cavalry use and submitted it to Ordnance as a prototype eventually this weapon became the 1919A2 air cooled BMG. Not to be outdone the Infantry, in 1931, requested the Ordnance Department to provide 72 Browning Tank Machine Guns for testing and development of field doctrine. Both the Cavalry and Infantry weapons had the 18” barrel with the slotted jacket. By 1935 the Infantry had concluded that a longer barrel was required and the now familiar 24” barrel was chosen. A parallel development was occurring at the same time as the Infantry and Cavalry were testing their new air cooled weapons. Ordnance resurrected Capt. Gorton’s bottom plate design, tuned it up a bit, and produced a new bottom plate which looks much like the plate we know today. For some inexplicable reason Ordnance decided to number this drawing of Capt. Gorton’s improved bottom plate C8464 the same number as the dovetail style M1917 bottom plate. We are not in possession of all of the drawings, however, it appears that this new and improved bottom plate was introduced into the system in the fall of 1936. We are in possession of drawing C8464 Revision 5 (1-15-37) which shows the familiar flanged bottom plate. Revision 5 also shows that this design pertains only to “BMG 1919A4”. Time marches on, and by February 1, 1938 the C8464 drawing had become drawing D35392, probably because of the ensuing confusion over two different parts that were not interchangeable, having the same piece mark and drawing number. There are only very minor dimension modifications between the two bottom plates drawings, and the “Drawing Pertains To” block on drawing D35392 shows 30BMG-M17(WC), 30 BMG-1919A4 FIXD, 30BMG-1919A4 FLEX, and drawing E1301 CASING, W/WATER JACKET ASSEMBLY, which is most likely the M1917A1 full sized Assembly drawing. E sized drawings were 40’’X necessary length, and to show a M1917A1 full size, you need a lot of paper. M17 is most likely a non standard M1917 or M1917A1 abbreviation. Right about now RIA became the Ordnance facility responsible for .30 BMG production, replacing the Springfield Armory, which was probably up to their necks in M1 Garand production. In 1938 RIA began to convert M1917’s and M1919A2’s to M1919A4’s, this fits nicely with the 2-1-38 drawing number change from C8464 to D35392. More than likely, some stock of flanged C8464 bottom plates had accumulated. Since, as of yet, we haven‘t yet discovered any C8464 imprinted bottom plates, it is not clear which Ordnance facility manufactured them. Enter the 1917 to 1917A1 rebuilding program. Official approval of the 1917A1 rebuilding/modernization/modification/conversion, these terms seem to have been used interchangeably, came on November 16, 1939 and specifically called out, along with a laundry list of other changes, the use of the D35392 bottom plate in the rebuild. Also included in this approval was notification that funds were available to convert 7,800 weapons. The M1917’s converted to M1917A1’s and some of the M1919A2’s and M1919A4’s that were previously converted from M1917’s required a slightly altered (shallower) milling depth of the inside of the bottom plate. This resulted from the fact that the original, unaltered M1917’s had the bottom of the side plates peened upward to hold the original dovetailed bottom plate in position. This peening reduced the height of the side plate by .020 to .040 inches and when the D35392 bottom plate was installed at rebuild, it changed the dimensional relationship of the internals to the casing. This created an interchangeability problem, as the modified weapons would not accept a standard C8464 flanged bottom plate, or new manufacture D35392 bottom plates. The fix for this was to mark either the C8464 or the D35392 plates modified to work on the M1917 or M1919 rebuilds with the drawing number, the letters “MP” signifying “Modified Part”, and the identification of which arsenal had produced the modified plate. The weapons with the non-standard bottom plates worked just fine, and now there was a simple way to tell new production weapons from rebuilds that required non-standard bottom plates. Just turn the weapon over and look at the bottom plate to see if it was marked with a MP suffix. Apparently, this was not deemed a good situation because it created another problem, confusion between MP and standard plates since the same drawing number, either C8464 or D35392 was on both. To remedy this new problem, RIA prepared a drawing showing ONLY the difference in the inside milling of the plates used on modified/converted weapons and a note to see drawing D35392 for all other dimensions. RIA/Ordnance numbered this drawing D37887 dated July 12, 1940 and began marking the modified plates D37887-RIA. It never fails, fix one thing and another problem appears, now there were three differently identified plates in the field all doing the same thing. Apparently, this was deemed a good situation. As of now we have not discovered any C8464-MP plates but have identified one M1917 to M1917A1 New England Westinghouse conversion in original configuration, right down to the original cam block screw staking, rebuilt at the Raritan Arsenal, at a time not known, and one 1917 to 1919A4 conversion, a semi-auto, that came as a kit with the left side plate attached to the bottom plate. Both have D-35392-MP RIA bottom plates. We have also encountered several RIA D37887 plates unattached to any other part of a weapon, and several built up into weapons or still attached to a left side plate, as an incomplete weapon. All D37887 encountered so far are RIA produced. M1917’s were converted to 1917A1 configuration not only at RIA (Rock Island Arsenal, Rock, Island, IL) but also at AA (Augusta Arsenal, Augusta, GA,) BA (Benicia Arsenal, Benicia, CA), MR (Mt. Rainier Ordnance Depot, Tacoma, WA), RA ( Raritan Arsenal, Raritan, NJ), RRA (Red River Arsenal, Texarkana, TX), and SA (Springfield Arsenal, Springfield, MA) It appears that all of the M1917 and M1919A2 to M1919A4 conversions, were performed at RIA. Apparently, units equipped with M1917’s shipped their weapons to the closest facility for either rebuild and return, or more likely they received rebuilt weapons, and used the crates to return the ones needing modification to the supplying facility. The M1917 to M1917A1 rebuild program extended all the way until the end of WWII. SNL A6, List of All Parts for Browning M1919A4 Fixed and Flexible; MM1919A5 fixed; and M1919A6, Flexible; and Ground Mounts dated 6 September, 1943 carries a note on page 21 “Note 1. Plate, bottom D37887 should be requested for guns that have been modified. These guns may be identified by the marking C8464-MP, D35393-MP or D37887 which appear on the underside of the bottom plate.” This note does not appear on the same publication dated May 1941 or ORD 9, the new designation for the “List of All Parts” document, dated January 1944. This tells us that the MP plates were no longer being produced, having been replaced by the D37887 plate, however there were probably lots of them in the supply pipeline. Identifying the bottom plate can be a little tricky. Obviously it is very easy to tell a C8464 dovetail plate from the C8464 plate with riveting flanges and integral T&E.. Some of the original dovetail bottom plates left from WWI may be piece marked 10C, most will not, most should have the manufacturers symbol : R in a triangle, Remington Arms Co, Bridgeport, CN, W in a circle New England Westinghouse, East Springfield, MA, C in a box, Colt’s Patent Firearms Mfg. Co. Hartford, CN The first drawing of the dovetail C8464 plate dated June 1, 1931 did not indicate placing a piece park on the part. The next available drawing C8464 Revision 1 dated 6-27-34 indicated that the parts produced from this drawing should be imprinted in 1/16” characters “C8464-1” between the cam block screw hole and the 4 holes for mounting the T&E bracket. The last drawing that we have of the dovetail C8464 plate, Revision 3, dated 3-15-36 still shows the “C8464-1” piece mark imprint required. According to this information, the only C8464 piece marked dovetail bottom plates will be marked “C8464-1”. As mentioned earlier, about 9-25-1936 the design of the bottom plate changed to the one familiar to us today. However, for no good reason that we can determine from this point in time, Ordnance kept the original drawing number, C8464, for a totally redesigned, and non-interchangeable part. The drawing C8464 (flanged) revision 1, dated 9-25-36 did not require a piece mark. The last available C8464 (flanged) drawing shows Revision 6, dated 1-15-37, still not requiring a piece mark. This does not mean that the parts were NOT piece mark imprinted it means that they were not REQUIRED to be imprinted. Enter the D35392 bottom plate drawing dated February 1, 1938, its virtually the same as C8464 (flanged), Revision 6, it does not require placing a piece mark either, but it calls out the piece mark D35392. The next available drawing is D35392, Revision 1, dated 3-10-39 still calling out the same piece mark but not requiring imprinting. Next comes drawing D35392 Revision 2, dated 3-19-40 which changes the piece mark to D35392-2 still no requirement to imprint the part, and the only observable changes in the part was a change in tolerance on the thickness of the riveting flange with the Revision 2 increasing the tolerances to +.003 from +.001 on the Revision 1 drawing. This also changed a couple of other tolerances up to +.006. The first mention of a piece mark imprinting requirement is on drawing D35392, Revision 7 dated 3-9-42 shows a piece mark requirement by Revision 6, but the drawing is torn and the piece mark area is missing We don’t have the Revision 6 drawing, but we have the date for Revision 6 it’s 1-19-42 and the required piece mark was, by backtracking the revision numbers, D35392-2. Now we have a piece mark D35392-2, AND an imprinting requirement with a date certain, 1-19-42. The next change in the piece mark is drawing D35392, Revision 10, dated 3-17-43. Revision 10 made a slight (1/64”) change in the tolerance of the radius cut on the inside of the riveting flange, and added a note about reaming the T&E holes “.4400-0015 REAM AT ASSEMBLY” The new piece mark was D35392-10. D35392-10 is, as far as we can tell, the final WWII version of the bottom plate. We have drawing 6535392 Revision 17, which was the revision that renumbered the bottom plate drawing yet again, and re-drew the drawing cleaning up all the revisions previously made dated 5-10-48. 6535392, a D size drawing, also changed the piece mark, now called a part number, to 6535392. This drawing also carries the imprinting requirement, and the notation “Was D35392”. In addition, we have observed one bottom plate marked 6535392-22 RIA this is believed to be Korean war vintage production. We, as of this writing, do not have a 6535392 drawing showing what Revision 22 was. If you kept the everything in the last several paragraph straight, you are doing very well. We have all of the drawings at hand, and I spent nearly 2 hours trying to get this right. Keep in mind, that if it’s a 6535392, D35392 OR a C8464 with a flange, no matter what the number suffix it is interchangeable, PROVIDING that it’s NOT marked with a “MP” suffix also. There is no evidence as of yet that any of the D35392-MP plates were manufactured any where else than RIA, or that any of the MP plates have suffix dash numbers i.e. -2 or -10. We suspect that RIA being in charge of the Cal. .30 BMG production produced all of the MP plates, but this just a supposition. We also suspect that RIA produced all of the D37887 conversion bottom plates, another supposition. What we don’t know is where the heck all, the C8464-MP plate have gone off to. An educated guess would be, there just weren’t all that many of them, and just like they used to say on the X-Files “They’re out there” we just haven’t encountered any of them yet. In addition, when piece marks started to be required to be imprinted on the parts, the manufacturer was required to imprint a code showing who made it. The known WWII makers of .30 caliber BMG’s, in addition to the previously noted WWI manufacturers are: RIA (Rock Island Arsenal, Rock, Island, IL) BA, BAC has been reported (Buffalo Arms Corp, Buffalo, NY) SG (Saginaw Steering Gear Div. General Motors Corp. Saginaw, MI. Some parts may be found imprinted “S.G.“ these parts are believed to have been produced by Saginaw‘s Grand Rapids, MI plant) BCI, BC has been reported (Border Cities Industries, Windsor, ON) Border Cities Industries was a General Motors, Canada subsidiary which manufactured BMG‘s chiefly for the British Commonwealth. Sometimes parts were produced by subcontractors, and those parts were marked with letters or numbers, codes to identify what subcontractor or even what subcontractor’s, or their own, production line the part came from. That is a subject for another day, and most likely, looking back nearly 70 years, we will never know for certain what all of the codes meant. Saginaw, we don’t know which plant, or why they did it, had a habit of stamping the Ordnance “Flaming Bomb” on the right riveting flange near the 4th rivet hole. Buffalo Arms, not to be outdone, took to stamping the required drawing number/part number/piece mark on the riveting flange, again, we don’t know why, when the drawings clearly called out imprinting the bottom of the bottom plate. Nearly every day something else comes up that defies logic and muddies the waters, but that’s what makes this stuff interesting. To sum all this up, there are various, or no markings on the some of the original dovetail bottom plates it could be marked 10C, C8464-1 or not at all. Some flanged bottom plates are from drawing C8464 and have MP suffixes, some flanged C8464 plates have no markings at all. Some D35392 plates are not imprinted with the drawing numbers at all and, as a practical matter, are all but indistinguishable from non-marked C8464 flanged bottom plates. Some are marked as “Modified Parts” (the MP suffix plates) Some have the drawing number D35392, but no number suffix, and some either a -2 or -10 suffix. Some plates are marked 6535392 with or without suffix. If you have a D37887 bottom plate, well, you pretty much know what it is, and who made it but not a very good idea when it was made, since the M1917 to M1917A1 conversions were still going on at VJ Day, August 15, 1945. By re-reading this, and comparing your plate to the pictures and text you should get an idea of about when your bottom plate was manufactured, and maybe by whom. If you think this has been a “hard read”, you should try writing it and trying to keep all the Revision numbers and drawing numbers straight. In this we think we have had some small success, but, no doubt, something slipped through one of the many cracks. In any event, we hope that the reader has found this material helpful. What success, if any, we have had in trying to shed some light on all of this, is due in no small part to the following: CREDITS AND ACKNOWLEDGEMENTS The Browning Machinegun Vol. 1 Dolf L. Goldsmith, Collector Grade Publications. INC Hard Rain, History of the Browning Machinegun, Frank Iannamico, Moose Lake Publishing LLC The aficionado of the Browning Machinegun would be well served by purchasing these books for study and reference. Jodie Creen Wesemann, Rock Island Arsenal Museum, Rock Island, IL contributed much to this effort, without her gracious assistance, we would still be struggling to grasp any of this. To all of the members of the 1919a4.com forum who examined their bottom plates and contributed to this discussion with comment and pictures, a sincere Thank You. Individual photos have credits cited per the providers request. This photo is of an original New England Westinghouse M1917 converted to a M1917A1 at the Raritan Arsenal. Note D35392MP-RIA imprint and the original cam block screw staking. Note the four bosses to the left of the T&E bracket which are present on all flanged bottom plates, they are designed to accommodate the pack frame for horse transport. Private NFA collection photo. This D35392MP-RIA bottom plate is from what we believe to be a fairly early M1917 to 1919A4 RIA conversion. It is now a semi-auto 1919A4 built up from a ”parts kit” that contained a barrel extension, bolt, and trigger with Westinghouse markings. The left side plate has two vacant rivet holes left over from the stirrup removal during the conversion. The parts kit also had an early style back plate with the aluminum stock escutcheons (grip panels). Photo courtesy of “CaptMax”. D35393-2 bottom plate manufactured by BA (Buffalo Arms Co.) The D35392 Revision 6 drawing required placement of the piece mark on the bottom of the plate. It is unknown why Buffalo Arms placed the marking in this location. Photo courtesy of Tim Gaine. D37887-RIA bottom plate used to convert M1917 and M1919A2 to M1917A1 and M1919A4 weapons. Photo courtesy of Rollin Lofdahl 6535392-22 standard (Revision 22) bottom plate. In May of 1945 drawing 6535392 Revision 17 replaced drawing D35392 Revision 16. This was the result of finally completing the 7 digit drawing number conversion that started in 1943. The conversion went so far as to continue the revision numbers from 17 onward. This plate is, most likely, Korean War vintage replacement part, as it shows little wear. Photo courtesy of Rollin Lofdahl Drawing 51-10-17 the reinforcing stirrup and the attaching rivet. Note that while the portion of the drawing shown is detail A on sheet 17 the piece marks are 17G for the stirrup and 17H2 for the rivet. Courtesy Jodie Creen Wesemann, RIA Museum Drawing B131261 the reinforcing stirrup. Courtesy Jodie Creen Wesemann, RIA Museum Drawing C8464 dovetail bottom plate WITHOUT flanges. Courtesy of Jodie Creen Wesemann, RIA Museum. Drawing C8464 bottom plate WITH flanges. Courtesy of Jodie Creen Wesemann, RIA Museum. Drawing D35392 Revision 16 dated 8-15-45 depicts the final WWII version of the bottom plate. This drawing shows the piece mark (part number) D35392-10. The black rectangular markings surrounding the drawing appear to be sprocket holes in the microfilm used for holding the film in position. Courtesy of Jodie Creen Wesemann, RIA Museum.

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