By Dan Shea
“The gun is a heat engine, used to convert the heat of exploding powder into mechanical energy, and as such is amenable to the fundamental concepts of thermodynamics. It takes propellant powder, rich in stored-up energy, and causes it to explode and produce gases at high temperature and pressure. These hot, highly compressed gases, confined in the powder chamber, expand, pushing the projectile in one direction and the gun in the other, the energy present in the gases being convert by this process into kinetic energy of the moving parts and into friction .- “The Thermodynamics of firearms” by Clark Shove Robinson, 1943
Notwithstanding the probable argument surrounding the use of the word “exploding” in regard to rapidly deflagrating powder, it would be hard to come up with a more concise paragraph clearly outlining the process of interior ballistics. I particularly like the concept of a firearm as a “heat engine,” which it is, but that phrase doesn’t come into most conversations down at the range or when preparing for a mission.
I recently had the honor of working to train another group of US Army armorers as they were preparing to deploy to Iraq. I consider it an honor every time. My goal is that they come away from training with a more thorough understanding of how the weapons work, an understanding that far exceeds the basic line item by line item, check them off as you read them, type of training that is seen in many technical classrooms. It has to go beyond, “You have reached this proficiency level because you read this item in the order it is in the manual.” There is more to it than that.
The SAR mantra that readers have heard from us so many times, that training for the combat zone requires live firing ammunition by all members of every unit whether they be infantry, SF, or support, and doing so frequently, extends over into the armorers’ groups as well. They need hands on with all of the variations of the weapons they will see, and they need to see them in all conditions from shiny brand new to worn out, beaten on, and malfunctioning. Mission accomplished.
I only hope that the SAR method of writing about firearms can contribute to helping everyone involved with military small arms gain a much better understanding of the fundamentals of how things work. Whether active duty military, law enforcement, industry professional, advanced collector or just plain firearms enthusiast, I hope we have helped you in your understanding of firearms, and helped you enjoy your interest more. On with Raffica…
Q-I was reading the Feb. 2006 issue and something caught my eye that puzzles me. In an article on the “Anthony Smith” upper receiver for the M11/9 SMG, it states that the ATF determined that a semi-auto variant of a full-auto gun with a fixed firing pin that fires from an open bolt is a machine gun. Since when? On what do they base this finding? 20 years ago those semi-auto guns were all over the place. What about current owners of those guns? What’s the deal?
A- Since when? Since about twenty years ago when those open bolt pistols were all over the place. The Technology Branch of ATF is responsible for determining the status of various firearms and parts. One of these categories is for a firearm that is readily convertible to a machine gun. Most of these open bolt, fixed firing pin semiautomatic pistols were very easy to convert to full automatic with simple tools and a couple of minutes of time. This was undeniably the case, so the government simply made a determination of their status and restricted further manufacture of them. Some were converted by individuals and registered as machine guns on Form 1s before 19 May, 1986, so you will occasionally see a registered MAC-10 or a KG-9 that is not an original, factory made machine gun.
The relevant information is contained in two rulings from 1982: ATF Ruling 82-2 that rules the open bolt KG-9 semiautomatic pistol is a machine gun, and ATF Ruling 82-8 that rules the various open bolt MACs, the SM10, the SM11A1, and the SAC (carbine) are all machine guns. Both of these rulings hold that these firearms, if manufactured before a date specified in the ruling (19 January 1982 for the KG-9, 21 June 1982 for the MACs) are not subject to the NFA restrictions. These guns are not considered to be machine guns. For the most part, the manufacturing dates were simple guidelines for the original manufacturers. There really isn’t a special way to tell the exact date of manufacture on these without access to the factory records, and both companies ceased any manufacture of the open bolt guns immediately on the ruling.
It would be prudent for owners, and especially prospective buyers, to function test these guns to ensure they are not capable of full auto fire, and to examine them for internal filing or modifications. To function check for full auto, simply point in safe direction, remove the magazine, retract the bolt to the rear and examine the chamber to see that it is clear. (If it isn’t, it would have fired any cartridge in the chamber unless there was a cartridge malfunction or a bad firing pin.) The bolt should be held to the rear by the sear, ready to fire in the open bolt mode. Holding the charging handle firmly, pull the trigger to allow the bolt to go forward into battery. Do not let off the trigger, keep holding it to the rear firing position. Retract the bolt to the rear while continuing to hold the trigger down. If the bolt is not caught and held by the sear, and the bolt will go forward, you have an altered gun that the ATF will consider a contraband machine gun. If the bolt stays to the rear, you should hear a click as you allow the trigger forward, as the disconnector resets. Repeating the cycle should show this is an unaltered semi-automatic open bolt pistol if the bolt continues to stay to the rear even if the trigger is still depressed.
If the weapon turns out to be contraband, you are required to turn it over to ATF or a law enforcement agency. If the offending altered parts were removed from the gun and destroyed, the unaltered pistol receiver and bolt would simply be for a semiautomatic. No one would be the wiser and that is the common “street” answer regarding this situation. However, that can get you in trouble as well. It is the stance of the agencies involved that an altered weapon like this must be turned in, and having the untaxed, unregistered machine gun in your possession even for the brief period before destroying the offending parts is a felony.
Q-When I was at Knob Creek in the fall of last year, there was a table that had four very rare BARs on it. One of them had a curved magazine and they called it the “303 BAR.” Was this magazine made from a converted Bren gun magazine?
A- I saw that collection as well – very nice. The two that really caught my eye were the top ejecting BAR and the .303 BAR. I don’t know if anyone bought the four guns at the show, but it sure would fill out someone’s collection of BARs. Bob Landies had a beautiful R75 for sale there at his tables, so it was possible for someone with the right bank account balance to really hit a home run on BARs at the show.
To your question; the .303 BAR magazine would more properly be referred to as the magazine for the Browning Light Machine Gun. That was the British name for the BAR in their trials. However, for the sake of uniform discussion, I will stick with the .303 BAR. The Browning Light Machine Gun trials pre-date the Bren gun by about ten years, so the idea of a .303 BAR magazine having been adapted from a Bren magazine is not really a possibility and the manufacturing processes were very different on the two. The most commonly seen variation of a .303 BAR magazine is the twenty-rounder that was on the gun you saw.
The first guns came from the US and were either Colts or Marlin-Rockwells. There were a lot of minor modifications done to the guns to accept the British cartridge. The most outwardly obvious is the radically curved magazine to accept the heavily tapered rimmed .303 cartridge. The magazine example in the ID photo is a British made one from BSA. There were magazines made in the US in small quantity, and eventually there were snail drums as well as thirty and forty-round magazines on the drawing boards. By 1930, the project was dead, and the bastard child of the ZB26, the incredibly reliable Bren gun, was the staple of the British military. In the ID photos, I did not have a file copy of the left hand view, but it is essentially a mirror image of the right hand view.
Q-I am a new Type 07 manufacturer who pays the Class 2 SOT and I have been working on making a DP machine gun from a parts set. I keep hearing about belt fed DPs, but have never seen one for sale. Is this an interchangeable add on, or does more work have to be done?
A- It is an add on part. But before we touch on that, I would really like to address your first statement to clarify an issue that will undoubtedly come up in the minds of many readers. The Type 07 FFL is a manufacturer’s license to make Title I firearms. These are your basic handguns, rifles, shotguns, etc. In order to manufacture a Title II firearm, that is firearms restricted under the National Firearms Act (NFA), a Special Occupational Tax is paid every year. This tax allows the taxpayer to manufacture and register silencers, short barreled rifles, short barreled shotguns, and firearms like pen guns that fall into the category of Any Other Weapon, for his own business purposes and for resale. The Class 2 SOT also allows the manufacturer to make new machine guns for sale to law enforcement and government agencies. It also allows the manufacture of machine guns for research and development. These items become “post 86 dealer samples” and they can never be sold to individuals and they can not be kept by the dealer on ending SOT status. Making a DP machine gun by a Class 2 manufacturer may sound unusual, but if it is in the process of that Class 2’s research and development, for understanding function as part of design, this is not generally questioned by the ATF. If it is simply to enhance a private collection, then there may be violations.
What am I saying? The Class 2 license isn’t a quickie way around the 1986 ban on further manufacture of machine guns for private ownership. If you are an aspiring designer trying to break into the field, and are doing legitimate and proper study of historical machine gun designs and the mechanical function, there historically hasn’t been an issue with ATF. If, on the other hand, you are making toys and putting videos of yourself firing your new “postie” antique on the Internet collector boards, then you aren’t comporting yourself in a business-like manner and you may have some future “issues.” Yes, please read between the lines here. More plainly put, if you are seriously in the business, the post samples you manufacture that are part of your legitimate work are fine. If you are only licensed for playing around, you might end up with personal legal problems and you may eventually be causing more restrictions and problems for the Class 3 community.
The Soviet era Degtyarev designed machine gun is fed from the top via a large flat pan magazine that lies horizontally on the receiver. Empty cases are ejected downwards. Several attempts to make this weapon a belt fed were tried during World War II – none were adopted. In the post war period, there were a number of trials for new machine guns, one of which resulted in the RPD in 7.62x39mm. Several Soviet designers worked on the standard 7.62x54R caliber idea for a light weight belt fed, and the base weapon of a DPM was chosen. This was not too complicated an idea, to make a drop on unit that was activated by transferring the energy of the DP charging handle to a lever that captured the handle in forward and rearward motion. The 1938 designed DShK is another machine gun that comes to mind that utilizes a lever that traps a knob attached to the bolt as a means of transferring that energy. While it may appear the idea is not too complicated, there are in fact a number of daunting challenges to this design. The DP machine gun bolt is a push forward system. It is very simple in that on its forward travel, it strips a round from the magazine and chambers, then fires the round. The cycle repeats on extraction and ejection. Russian belts, however, require that the round be pulled to the rear, out of the belt, due to the rimmed case. The 7.62x54R cartridge does not lend itself to links such as the M13 (M60 or M240) link that allows the 7.62x51mm NATO cartridge to strip forward.
When the rimmed cartridge is pulled to the rear, it must then be presented to the DP bolt for forward travel. Since the DP pan covers a large, flat area of the receiver, there was enough room to feed the belts into a forward part of the device, activate all of the mechanism with a lever, and capture and move the cartridge to a rearward position for presentation to the bolt’s forward motion. Note the toggle underneath the rear of the top cover in the photo. This is a spring-pressured lever that guides the cartridge downward into the path of the bolt, and holds it in place as well. This lever is also evident on the PK series of machine guns and, in my mind, is one of the primary reasons the PK is so reliable. No matter what the orientation of the PK, the cartridges are positively presented to the bolt. Designs that rely on gravity for that presentation have more reliability problems.
The Rotniy Pulemet Obrazsta 1946 or RP46 was manufactured in small quantities and adopted in service. Since there is no other modification needed to the DPM, the upgrade to belt feed could be readily accomplished in the field on existing guns with the unit pictured here. One issue that had a large impact was that the DP series guns do not have a quick change barrel and with belt fed firing, the barrels could overheat quickly.
These RP-46 belt fed units are exceedingly rare in the United States. I have only seen a few for sale and they are snatched up quickly. Like any add on part, there may be a bit of adjustment needed to make it functional, especially on a re-welded receiver. Proper alignment of every part is imperative to get the mechanism to work. The RP-46 uses the Russian standard 1910 Maxim style non-disintegrating metallic links, still used in the PKM today.
Q-What are Dater Holes?
A- I have to assume you are referring to the Gemtech product line. In some of Gemtech’s suppressor baffles, there are mysterious holes that Dr. Philip Dater refuses to discuss. He says they are proprietary to his designs, and will not reveal the technology involved, stating that this is simply the result of his many years experience in suppressor design. After I got your question, I went to my reference collection of silencers and started taking apart some of his designs from the 1970s and these “Dater Holes” were not there. I didn’t bother going any further on this to find at what point in his designs these appear, and would not like to speculate as to the real purpose. If you are not referring to the suppressors, and, heaven forbid, you are referring to something anatomical, then the only other reference I could imagine for “Dater Holes” would be the inexplicable wormholes in the time-space continuum that it is rumored that Dr. Dater uses for international as well as intergalactic travel. It is probable that he learned of these when he worked at Roswell during his military career back in the early 1950s, but I would be speculating. Explaining any of THAT is far above my pay grade.
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SAR Magazine ID Guide:
Magazine: .303 caliber Browning Automatic Rifle
Manufacturer: British BSA (Birmingham Small Arms factory)
Notes: Magazine is made of two stamped halves welded together. This example has “15” painted on the
Category: RDC2B (Rifle caliber, Dual column, Curved, presents from two columns, Box style)
Caliber: .303 British
Capacity: 20 rounds
OA Length: 6 1/4 inches
Backstrap: 6 3/8 inches
Max. Width: 3.590 inches
Body Width: 3.160 inches
Max. Depth: 1.140 inches
Body Depth: 1.000 inches
|This article first appeared in Small Arms Review V9N7 (April 2006)