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The Helical Feed Magazine (9mm)
This is informative and , in it's own way, rather interesting reading, but it is a bit dry, and perhaps more detailed than the casual reader might want. The patent is a general description of the workings of the magazine, and it may be noted that the patent covers the use of this design for cartridges, as well as paint balls.
These magazines are constructed of fiberglass reinforced plastic, will
not rust, and are surprisingly light and sturdy. The magazines may be stored
loaded without shortening the life of the magazine spring, by releasing the
spring tension. Disassembly is fairly simple, though the magazines should
rarely need cleaning. The above diagram would seem to suggest that taking
these magazines apart is is a non-trivial task, and that those wishing to
avoid disaster might want to give this a second thought. Loading may be accomplished
by simply inserting the cartridges one by one, or through the use of a special
crank wound tool sold for rapid reloading. There is a winding crank with
a folding handle located at the rear of the magazine housing. It may be necessary
to turn the crank a couple of times, putting some tension on the spring,
to bring the magazine follower up to the feed lips. Once this is done, the
rounds may be loaded against the slight pressure of the follower. As the tension
of the spring increases, it may be released by pushing on a small button
located in the center of the winding crank. Once the magazine is completely
loaded, this button may be depressed to completely remove tension from the
spring, for long term storage, while loaded. With the tension completely
removed from the spring, these magazines must be wound like the old Thompson
style drums. The correct tension is:
If the worst should happen, and you damage your magazine, or it wears out, there is a repair service affiliated with the "unofficial Calico web page" given in my links. As of this writing, the charge is $30 plus the cost of shipping and parts. This will likely put the total cost at around $50-$100, cheap compared to the cost of replacement magazines, when they can be found. Parts are still available from Calico, though they will no longer sell a civilian one of their magazines. There are magazine repair kits available for the adventurous (or the cheapskate, who does not wish to part with an extra $30) The repair kits contain the internal workings of the magazines. There is also an outer shell kit, which contains the external parts. So restrictive are the provisions of the magazine ban, that these parts must not be shipped, or even stored, together. Doing so would constitute a contraband magazine in the eyes of the B.A.T.F. The total cost of the parts required to construct a 100 round magazine would be around $170. This cost does not include legal fees, the cost of your confiscated gun collection, and jail time, if you are ever caught with it. Possession of all of these parts, assembled or not, would also make you a felon, and would prevent you from ever legally owning a gun again. If only real crime were taken this seriously, and actual criminals treated this harshly. This situation will end in 2004, unless the powers that be vote the ban into permanence. In the meantime treat these magazines as if they are gold; ounce for ounce they are about as valuable.
The photo shows a modification of the original snail shell magazine, made for use with the AK-47 series of assault rifles. It is shown in company with the 50 and the 100 round versions of the Calico magazines, for size comparison. The AK drum holds 75 rounds, and it can be seen that it is much larger than the Calico mags. I can personally vouch for the fact that it is also much heavier, and, despite it's weight, much more delicate. These AK mags are a direct development of the Soviet PPSH mag, one of which is shown with it's cover removed, in the next photo. There is a variation of the AK drum magazine which will fit on an M-16 rifle, and has been modified to feed the .223 round. All of these drums owe their design to the 32 round "snail shell" magazine in 9mm, for the Luger pistol. This was a development for World War One, and was an attempt to give the trench bound soldier greater firepower in a smaller package. tactically, this was the precursor to the submachine gun. This same magazine was used on the German MP 18 submachine gun, though it was later replaced with a more conventional box type magazine. The 9x19 round of the Calico, and the 7x39mm round of the AK are also shown for comparison.
The drum mag of the Thompson works on similar principles, but is modified somewhat. The Thompson drum has no feeder column, and so can only be fired in the 1928 model Thompson, and others designed specifically for it. These weapons do not have magazine wells in the traditional sense, but use a cut out in the frame instead, with multiple locking lugs for the magazine instead of a single catch. The Thompson drum will not fit on the later "M-1" Thompsons produced for use during World War Two, because this model lacks the cut out in the frame. Drums for the Thompson were typically of the 50 round capacity, though there was a large, heavy, and cumbersome version which held 100 rounds available.
In addition to the "true" drum magazines, a number of drum style magazines have been produced. The more common versions of these tend to be simple ammunition carriers, rather than actual magazines. These ammunition carriers function as storage boxes for belts on belt fed guns. Guns using these systems, generally feed from the bottom, in the fashion of a magazine fed weapon, rather than from the side, which is the more common method used by belt fed weapons. The old Stoner system, along with the Soviet RPK light machine gun used "magazines" of this type. The other type of "drum style" magazine is actually a standard box magazine which has been curved sideways into a complete circle. The only advantage to this type of magazine is that it does not protrude as far from the magazine well as a straight version would. I am aware of only one example of this type of magazine. It was produced for the AR-15/M-16 series of rifles, and was of molded plastic.
Compared to the simple elegance of the helical design used in the Calico magazines, the other drums seem quite primitive, and crude. These other magazines are also considerably more complicated, and delicate internally. They are also all, much harder to load, needing to be opened for loading, and then loaded in stages. The Calico magazines, particularly with the addition of the rapid loading tool, are quite simple to charge. In addition, the more traditional drums are heavy, and their stamped metal bodies are easily dented, and damaged, and susceptible to the effects of corrosion.