By Dan Shea
For it’s Tommy this, an’ Tommy that, an’ “Chuck ‘im out, the brute!” But it’s “Saviour of ‘is country” when the guns begin to shoot. – Rudyard Kipling “Tommy”
Greetings once again from the Land of Raffica, where I am pleased to see that you can now buy an almost endless cloth 22lr belt for your Tippman 1919, and make a belt of plastic linked 22lr of almost any length you wish. For shooting fun, it is hard to beat a 22 caliber machine gun, and I bought a bunch of these links at Knob Creek from Lakeside Arms. Then, I had to have more when I saw Lakeside at the SAR show in Phoenix. If we could just get someone to make a .22 caliber Minigun using a backpack mounted hopper feed, recreational machine gun shooting would achieve new heights.
Two new machine guns grace my personal collection now, and this is a very happy thing. One is a 1909 Colt Benet Mercie variant of the Hotchkiss Light Machine Gun. Robert Segel, Senior Editor SAR, has a pretty good take on this weapon, and I will let him go after it- but this expands the working reference collection on the Hotchkiss guns to seven. I plan on doing an article on how the Hotchkiss guns work soon, so this is a good thing. The other addition is a 1924/29 Chatellerault Light Machine Gun, which I have been saving an AA sight for since the last Great Western Show happened in Vegas. Ah, it’s been a good Christmas.
There are only a couple of questions this month for the newly resurrected Raffica column. One is from an historical machine gun shooter, another from an active operator. I will try to get these answered in the spirit of the end user’s needs.
Q- I found a box of early Browning belts in a can at a gun show. I asked a friend and he said they were probably Potato Digger belts. Can I use Potato Digger belts in my 1919 Browning?
A- This question is sort of backwards. True potato digger belts are hard to find and should be treated with a bit of reverence. So, “Can you use 1919 Browning belts in your Potato Digger?” might be a better question. By the way, if you do, in fact, have a stock of original Potato Digger belts sitting there, I know a whole bunch of motivated individuals who would like to buy or trade you out of them. If you insist on using the Digger belts in a 1919, look at the pictures in this answer and the reverse will be true for your situation.
The pitch was very slightly different between the original cloth belts for the Colt and Marlin Potato Diggers and John Browning’s 1917/1919 series of machine guns. What I mean by “pitch” is the spacing of the cartridges in the belt. Each machine gun model has been designed to function in a manner where the recoiling parts cycle a feed mechanism using energy gained from the expanding propellant gases driving the projectile forward. In the case of the Potato Digger, actual gases bleed out of a hole in the forward portion of the barrel operating a downward cycling lever. If the gun was mounted too close to the front of a trench, it would throw dirt in the air, thus the “Potato Digger” moniker. The action of this lever causes a number of activities inside of the receiver. The bolt carrier assembly moves to the rear, and there is a cartridge feeding wheel (Arrow Figure 1) which is set to properly present the cartridges to the cartridge extractor on rearward motion of the moving parts group. If the cartridges are not presented to the wheel in a manner that matches the “Pitch” of the wheel, then the wheel will crush the cartridge from the side, causing a feed jam. Potato Diggers are notoriously picky to work on, so jamming it up is a “Bad” thing. You can even get to the point of pulling sideplates off if it gets too bad.
The Browning 1917/19 cloth belts are a slightly different pitch from the early Digger belts, but there are two other problems that will immediately present themselves when you use the 1919 belts in a Digger. First, if the belt has a steel lead tab it will be too wide to fit the belt exit hole in the right sideplate. (Brass leads should be fine) You can file the sides of the steel leading tab to make them fit, it won’t hinder the belt being used as intended in the 1919. The second problem is a bit more serious but easily surmountable.
In the photo comparison in Figure 2, I put an original 1914 Potato Digger belt on top of a 1919 Browning belt. The 1914 belt is at “A”, and should illustrate how deeply the cartridge can be seated into the belt, compared to the 1919 belt “B”, where the cartridge is much shallower. This is due to the fact that 1919 series belts are stitched much deeper than the Digger belts. I also used these two belts because there is EmmaGee lore that the Digger belt and the 1919 belt have different amounts of horizontal stripes on them. In this case, both belts only have one black stripe along them. Both belts are original. The multiple stripes ID method is not always true, but according to Bill Vallerand and the late Herbie Woodend, all of the Digger belts are stitched to a short pocket at the top. The net effect of the different seating depths is immediately evident if you try to use one type of belt loader for a different type of belt- they just won’t do a proper job without the operator paying close attention. The arrows on Figure 3 show a proper Potato Digger belt placed into a 1914 Digger, and Figure 4 shows a 1919 Browning belt positioned so that the belt will exit the belt channel on the other side of the receiver. This graphically shows the problem with using a 1919 belt in a Digger. I have had the Digger work with it, no problem. In reality, there is a slight placement problem that can “Kink” the belt as it leaves the belt exit port, and stop a feed. Bill Vallerand’s advice is that when you put the 1919 belt in a digger, give a serious tug on the leader as you charge the gun, thus properly seating the first cartridge and positioning the belt to bend slightly and smoothly come out. It might even be necessary to keep tension on the belt as it comes out.
Browning metallic links can also be used in the Digger, but you need a small piece of sheet metal around the sprocket to guide the links out of the receiver. This is called the “Dutchman’s Britches”, and is already in the Marling guns. Early Colts won’t have it.
For those of you who are working on making new 1919 belts, think about making some digger belts. Oh, and while you are at it, try and make some spaced for the 7.62x54R Russian 1917 Diggers; we have never found a belt to feed these!
Speaking of using 1919 belts in other guns, while we were doing the last Maxim / Vickers class at LMO, Dolf Goldsmith insisted that 1919 belts would work in the Maxim MG08 and MG08/15 series guns. We were all looking at each other, wondering what Dolf was talking about. Much hubbub ensued. Dr. Ed Weitzman tried to bring a modicum of reality to the discussion, but Dolf was insistent and grabbed an old used belt from my pile, then loaded it with 8mm. On range day, Dolf put it into Tony Dee’s 08/15 and it ran like a champ with no stoppages. We gleefully ran over and put it into an 08; with the same result. I hid the belt from everyone, hoping to still have it later for myself. Discussions flourished about how to “age” Browning belts so they would be loose enough to use in Maxims, but Dr. Ed Weitzman clarified the issues for us that we should be using the proper belts at all times. However, I am still going through my Browning belt pile and looking them over very carefully
Q- I have been looking for a way to shorten my M16A2 barrel- it is M4 style and I am doing door to door work and would like to have more leeway on entry. I read that if you shorten the barrel, you have to change the timing. How do I do this? – email from Iraq
A- This is really more of a training issue than a mechanical one, but this is the age old “Shorty” question and perhaps it needs another shot at addressing it. First, since you are in combat, I would caution you on altering your issue weapon. The barrel length and twist are designed for certain ammunition, to achieve certain results when hitting your targeted bad guy. The terminal ballistics have been addressed very well by Dr. Martin Fackler and the International Wound Ballistics Association and are not really relevant to our discussion of mechanics, but they truly are relevant to your use. I urge you to consider the differences should you have to use your M4 at longer ranges than just in clearing ops. Personally, I would stick with the 14.5 inch barrel.
All too often, a problem gets misstated and is therefore incorrectly answered. Since the inception of the AR15/M16 system, people have been trying to change it. Many times this has led to success, but all too often to dismal failure. Most of us are familiar with the story of the initial problem in field use in Vietnam; the rifle was designed to use a certain type of ammunition, and the government OK’d the change of propellant type. In the field this equaled disaster. Gene Stoner once said that people have been trying to fix the system ever since, instead of going back to what the original propellant was.
It is the same thing with shortening the barrel. Stoner explained this once to me, and Reed Knight and Doug Olson did a lot of work to clarify this issue. At first, a group of us had been trying to retard the timing of the release of the hammer during full auto fire, with a ten inch barrel on the M16. (These were notoriously unreliable). We did this by heating the auto sear and bending it forward just under five degrees. This was a “Timing” issue. The bolt carrier would strike the autosear tripping the hammer just a millisecond later than normal. In many cases this “Fix” worked.
However, it does not address the real issue as stated by Stoner. This is an issue of time under pressurization for the gas system.
Gas 1 As the projectile moves down the barrel being pushed by the expanding propellant gases, eventually it reaches the gas port under the front sight. As soon as it passes the gas port hole (A), the propellant gases expand to fill the gas tube (D). The system is now pressurized. As soon as the projectile exits the bore (B), the pressure drops off. The time that the projectile takes to travel that distance (C), is the “Time under pressurization” for the system. In the photo example here, this is a Colt Model 605a Cutaway, and the distance is very short compared to the distance in a standard M16 barrel.
Gas 2 At the other end of the gas system, there is work that has to be done to unlock the bolt head. This is done when the still expanding propellant gases fill the gas tube under pressure- and the rear end is against the gas key on the bolt carrier. The bolt carrier is held forward under spring pressure from the return (Recoil) spring, and the gases press against the assembly to the rear (D). As the bolt carrier body (A) travels rearward, the cam pin (B) travels in its cam path on the body, rotating the bolt (C)anti-clockwise (operator’s view) and unlocking the bolt. This is all timed so that when the projectile leaves the bore and pressure drops, the system is unlocked, remaining inertia cycles the bolt carrier rearward, excess gases are vented out the bolt carrier body venting system, the return spring returns the bolt carrier to the locked position after stripping and loading the next round. It is critical that there is enough energy to return the bolt carrier fully to the rear, or short cycles occur. Improper extractions, stovepipes, but more typically rounds jammed against the barrel extension occur. It is a lack of time under pressurization that keeps the system from achieving the final, critical rearward motion of the bolt carrier to an acceptable point.
Gas 3In this sequence, the gas tube/ gas key/ bolt carrier relationship can be seen as the bolt carrier moves to the rear, eventually freeing the gas key from the gas tube end and venting excess gases into the upper receiver area.
Some “Cures” that have been applied have been the change to timing as discussed at the beginning of this answer, increasing the volume of gases as is done with the pigtail gas tubes- longer tubes equals more volume, not more time under pressure, and the age old “Cure” of making a larger gas port hole. The gas tube is thicker at the front to fight the erosion that occurs during the pressurization- extremely hot propellant gases burn the front of the tube. Opening the gas port hole without addressing the front section of the gas tube simply increases the burnout rate of the tube. Over cycling the gun will also do this- and is a frequently occurring problem with “Shorties.” When you fire a carbine a lot and the cyclic rate starts approaching 1200 rpm, this may be either “Fun” or “Lay out a field of fire” depending on where you are, but it is very unhealthy for the gun.
Gas 4 In reality, the best cure is to keep as long a distance as possible between the points where the projectile passes the gas port and where the bullet exits the bore. In this photo, we can compare the original Colt M16A1 barrel length (Bottom) with a full 7 inches of travel for the bullet after passing the gas port hole, to the Colt Model 605A with 2.5 inches of travel (Typical of most “Shorties” from that era) and the final barrel length as used today in the Colt M4 Carbine, where the distance of travel has been returned to a full 7 inches. I hope this answers your question on the barrel length, and why many of us feel that you, especially, should keep the full length of your M4 barrel for reliability’s sake.
Q– What is an RKI? I keep hearing it mentioned in different places, and it is almost always attributed to you.
A- An RKI is a “Reasonably Knowledgeable Individual.” I came up with this term many years ago, (Late 1970s or so) to replace the somewhat uncomfortable term “Expert.” It is an old axiom that many “experts” are boring and tend to fight amongst each other for imaginary positions as to who is the most knowledgeable- and once you are an “Expert,” you are a target for all the other “Experts” and “Wannabe Experts”. This in no way is intended to insult those who have a tremendous amount of knowledge on a subject, and have spent much time and energy to become more than just conversant on a subject. I mean no disrespect by saying RKI. I simply do not like being in a position where I can’t still be learning, where I can’t be incorrect on something, where I can’t just hang with everyone else. I don’t want a private “Expert’s table” to sit at.
Typically with “Experts” and especially in academia, credentials are more important than anything else. Many a time I have sat with someone who was a self styled expert on an issue, and they made a comment and were wrong. Another person would correct the statement, and the “Expert” would attack immediately, demanding credentials. “Where are your credentials?” said in an imperious tone. I have sat and listened and a few times pointed out to the “Expert” that it doesn’t make a difference if the guy is Joe Sh*% the Ragman with a fourth grade education, if he is right he is right and that won’t change because he didn’t go to Harvard and get a PhD.
There are people who are truly experts in our field. Over the years, quite a few of them have taken the time to teach me about the history or technology involved in machine guns or Class 3. I consider that a blessing. It’s nice if we can have an atmosphere of sharing knowledge and experience, and SAR is meant to foster that atmosphere. We hope to continue with that, and to bring many more RKIs to these pages. If you want me to find an answer for you, drop a line with the question. For space reasons I will probably edit it down, and won’t include names unless you request it. – Dan
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|This article first appeared in Small Arms Review V8N6 (March 2005)|
and was posted online on June 7, 2013