Monday, January 31, 2005
Cold War Manufacturing
Probably the best-known military rifle is the AK-47, of which at least fifty million were built (some say closer to twice that many) since being invented by a survivor of Russia's struggle against the Nazis in WWII. And while never used by the United States and thus somewhat less familiar, the FN-FAL was the most proliferic rifle used in the free world in the 40 years following WWII.
Starting with the foundation of any rifle, the receiver also yields the most obvious clues as to the differences between these two weapons, and indeed, the cultures that produced them. While the first AKs used a milled receiver, a stamped-steel sheetmetal part was implemented relatively quickly, with small milled inserts ("trunnions") riveted-in to provide attachment for the barrel and stock. Even in the milled form, the receiver is exceedingly simple, consisting of relatively few features and certainly none that could be considered "delicate". The bolt rails are smaller stampings that are riveted in place. The bolt locks into the front trunnion, meaning that the receiver has no impact on headspacing, nor does it have to withstand the forces generated by the cartridge. The recoil spring loads are dumped into the rear trunnion, and from there directly into the stock and the shooter's shoulder. As such, the receiver does little except to roughly locate the barrel assembly, stock, and FCG in the same general vicinity.
On the other hand, the FAL employed a two-piece receiver. While the lower half is stamped from sheetmetal, it's of a considerably heavier gauge than that used for an AK, requiring disproportionally heavier machinery. The upper receiver was milled from a solid forged block for the first 20-some years of production, up until the substitution of an investment cast part near the end of the rifle's production run. DS Arms claims that their milled receivers start with a 19-lb block of billet. Compare that to the 4 ounces or so of sheetmetal used for a stamped AK receiver. The rails for the bolt and carrier are milled into the inner walls of the upper receiver. The bolt locks into the receiver, meaning that the loads caused by firing of a catridge (around 50,000 PSI in the 7.62x51 NATO, or about 12,500 pounds of force at the bolt face) are dumped into the receiver, which needless to say requires some considerable "beef" between the barrel and the locking lug. Since there's such a span between those two areas, the headspace must be set via locking lugs of varying thickness. Where as the magazine well on the AK receiver is nothing more than a hole and a couple of stamped bumps, it's an extension of the upper receiver forging on the FAL.
The AK uses a very simple bolt and bolt carrier. As mentioned before, they ride together on stamped rails, with relatively large clearances (a lateral clearance of 0.100" would not impair function). The rotary bolt generates substantial force via camming action to remove the spent cartridge casing, and the gas piston follows the bolt assembly all the way through the stroke to make sure the carrier completes its intended travel. The gas system is unadjustable, and presumably is set to operate with an absolute minimum of pressure.
The tilting-bolt action of the FAL requires that the gas system provide the extraction force directly, with no mechanical advantage (of course, with the 5,000 PSI or so acting on the piston, the job usually gets done). The bolt carrier rides in the aforementioned machined cuts, with clearances of perhaps 0.010" or so (certainly less than the typical grain of sand). The adjustable gas system is great for those using a variety of ammunition, but that's not all that likely in a combat situation, and thus simply adds additional complexity and yet another way for the operation to impair function.
The fire control group of both rifles is substationally different not in design, but rather in execution. The FAL FCG has a number of small features, providing relatively crisp feel but also increasing the difficulty of manufacture and additional susceptability to failure. On the other hand, the AK FCG has features perhaps 2-5x larger, and thus is not only less sensitive to manufacturing tolerances, but also to environmental contamination.
Springs are essential to the function of any firearm, and are certainly among the more difficult parts to control in even a modern manufacturing setting. The FAL uses 19 springs, many of which work through plungers and so on. The AK uses a total of six springs (seven if you count the plunger for the muzzle brake on some variants), and the design of the recoil and FCG springs show particularly exceptional simplicity.
So what's the result of all this? Well, if I had to go set up some in some third-world country a few decades ago, there's little doubt which one would be more feasible to produce - and if you haven't been paying much attention, that's the AK. But having built examples of both, I can safely say that the AK also takes far more time to assemble from individual components. If you've got more manpower than equipment, then the AK is the way to go. And if this rifle is going to be used in any environment, it's also a safe bet that the extremely loose tolerances of the AK will allow it to function where the "tighter" FAL simply will not. But the combination of those fine tolerances with a substationally more-powerful cartridge means that the FAL allows a rifleman to engage targets at a far longer range (the 7.62x39 cartridge of the AK is useful to perhaps 200 yards but not much further, where as the 7.62 NATO cartridge, with its heavier bullet and much higher muzzle velocity remains lethal out past 600 yards). That's a further clue to the doctrine of the two participants in the Cold War, and the relative value one can infer that each placed on its soldiers.