“they don’t always go bang”
if you intend to acquire a firearm as a personal defense weapon, you should be aware that just as any other machine a firearm may fail to function as intended, and even finely made firearms don’t always “go bang” if you haven’t taken steps to assure proper function.
in this regard the ar-15 series of rifles is no exception. and, even though the rifle has benefited from some 40 years of development and refinement dedicated towards making it dependable, it does possess several design weaknesses centered on the function and reliability of the bolt. these weaknesses are not so serious as to compromise the integrity of the weapon, and to this day, further semi-automatic combat rifle development still copies the basic design features discussed below, so the system must have continuing attractiveness and viability to weapons’ designers. still in all, the prudent owner of a weapon will keep certain function issues in mind, learn how to deal with the mechanical and physical steps to deal with them, and take the proper precautions in terms of maintenance and parts kept on hand for repair.
the heart of an ar-15 is a rotating and reciprocating bolt, whose movements are imparted to it by a bolt carrier which moves it back and forth, and which rotates the bolt into battery, or locks it, by means steel rod cut through a helical cam in the shaft of the bolt. it all sounds very complicated, but a visual inspection of the bolt and carrier upon disassembly of the rifle reveals the logic of the system in a glance.
when the rifle is fired, propellant gases from the barrel are siphoned off and travel in a tube back to the bolt carrier and bolt, and push the bolt carrier rearward. as it travels rearward, the steel rod in the bolt carrier operates on the angled surface of the cam, causes the bolt to rotate. when the bolt rotates, the lugs projecting from its surface move away from contacting corresponding projections in the barrel extension, and into line with slots in the barrel extension, and past them to the rear as they are carried away by the bolt carriers rearward movement. the spent case is held against the face of the bolt by a lipped piece of metal mortised into the bolt face, the lip on the extractor holding onto the rim of the case as the lip projects into a recess in the milled into the case ahead of the rim. as the tip of the spent case clears the confines of the receiver past a hole milled in its side, the case is ejected from the firearm by the pressure of a small plunger milled into the bolt face, the cartridge pivoted outward around the point where the extractor has held onto it from the chamber. the ejector and extractor work in tandem to achieve the ejection of the case as described. the bolt is pulled back until it is behind the magazine which holds the next round to be fired at its top. the bolt moves forward, a lower lug passing through a slot cut into the back of the magazine where it contact the rear portion of the next round, and shoves that round forward and into the chamber of the rifle, but not until the extractor has a chance to pivot on a hinge, allowing the round to come fully into contact with the bolt face as the lip of the extractor slips into the grove cut into the shell casing.
this happens at great speed, and the whole process is subject to great mechanical stresses. the gun powder, a controlled burn rate propellant, generates nearly 60,000 pounds of pressure very quickly as it turns into hot incandescent gas, expelling a bullet from the ar-15 in .223 caliber at anywhere from 3200 feet per second to 3400 feet per second, depending upon the weight of the bullet in the round. this force pushes against the bolt face while the bolt is held in battery, and though it is largely dissipated by the time the bolt cycles, you can imagine the heat and the battering to which the rifle mechanism is subjected to each time a round is fired.
enter the first design flaw.
one of the locking lugs is not quite as strong as some of the others, given its placement upon the bolt in an area where because of cuts in the bolt not as much metal exists to support that lug as the other lugs. this lug is subjected to a predictable rate of failure, usually in the form of cracking, deformation or even chipping or breakage. this has become so well understood, that some manufacturers have simply fallen upon the manufacturing expedient of omitting that lug from the bolt: the bolt is sufficiently strong as built that it is not weakened structurally by the omission, and the bolts ability to withstand and contain the pressures of the powders ignition is not compromised in the slightest.
it is therefore quite common, and entirely a proper expedient, for users of ar-15’s which are going to be subjected to heavy use to have on hand, in a parts kit, a spare bolt for field replacement should the bolt fail during combat, or should such failure be discovered during routine maintenance after combat operations if the failure did not lead to the weapon ceasing function.
enter the next design flaw. to which i was subjected.
i owned an ar-180b, a designed somewhat different from the ar-15, but which has a bolt nearly identical to the ar-15, and absolutely identical in the design feature which “failed.” this rifle began to fail to eject, and then to operate, after prolonged use. upon inspection upon disassembly, it was found that the ejector, the little spring powered plunger fitted in a cylindrical hole milled into the face of the bolt, was “frozen” in place, projecting from the face of the bolt. in such condition, the ejector caused the operational cycle of the weapon to jam, either not allowing a cartridge to present in a straight line to the chamber as it was not flush with the bolt face, or so as to cause an empty case not to eject as the plunger was imparting no motion to pivot it around the extractor.
further disassembly revealed the culprit in the form of thousands of tiny little brass filings that had somehow migrated down the cylindrical milled hole, past the very small mechanical tolerances between the ejector and the bolt, to lodge in the space where the ejector spring was housed, completely preventing the spring from imparting any force to the ejector, as the ejector eventually was prevented from moving into that cavity and compressing the spring. i took the rifle to don manning of shooter’s supply in yakima, washington describing the problem to him and showing him the disassembled bolt and ejector, all the while expressing puzzlement as to how this should have come to pass.
he said not a word, but disappeared into the back of the shop and bringing back a small rod of arkansas whetting stone, the end of which was very close to the diameter of the bolt face of the weapon. here, he said, polish the face of the bolt with this, using a circular motion, just “twirl” the stone between your fingers, and using lots of machine oil to clear the grit. polish it until you remove irregularities or roughness from the face of the bolt, especially any machining burrs which may be around the edge of the hole in which the ejector is fitted.
ah, i said … .
not the first one of these i have ever seen, he said, nor the first one ever encountered.
that would explain the fact of the diameter of the rod being the same as the diameter of the bolt face, i said.
not too bad for mostly rock, he said laughing, and not referring to the stone that he handed me, with a big smile on his face.
i took the bolt home, and polished the face, and sure enough, in the process removed a tiny burr around the recess cut for the ejector, a burr on the side of the hole that was the “forward face” of the hole turning into the face of the cartridge head as the bolt rotated in the recoil cycle. keep in mind, that the operational cycle of the bolt does not take place in a leisurely manner as the weapon is fired: i do not know the rotational speed of the bolt, but the bolt face is subjected to many thousands of pounds of pressure by the cartridge brass held against it by the force of the remnant propellant gases, and the bolt face turns very quickly. the irregularity of the bolt face, plus the hardened steel burr, where cutting the tiny shavings every time a round was fired, and the forces involved where forcing the shavings into the milled recess housing the ejector, and packing them in there so tightly that the bolt ceased to function.
enter the next design flaw. a design flaw to which i was also quite recently subjected.
about two years ago i purchased an upper receiver assembly for my ar-15 in 6.8 mm remington spc, which is a little larger caliber cartridge than the .223 remington, the 6.8 mm bullet being about .270 caliber. recently i mounted an eotech 552 night sight capable optic, did some other preparation work, and mated the upper receiver assembly to an ar-15 lower receiver. on the day that i wanted to take the rifle to the range i decided that i had best test some basic functions of the rifle, such as confirming that it would strip a round from the magazine and chamber it properly.
so, a loaded magazine was placed in the rifle, one round, and the bolt pulled back and released, to see if a round would go in the chamber as designed. (yes, the rifle was pointed toward several boxes of old magazines against a concrete wall in the basement of my house, and no way was an errant round ever going to leave that basement.)
and the round would not chamber, and the bolt did not go forward sufficiently to allow the bolt to pass through the slots in the receiver/barrel extension: in short, the bolt did not go forward enough even to begin the rotational motion that ends in locking the bolt into battery: in this situation, the rifle is not capable of firing, a blessing really, because an a cartridge unsupported by the rifle’s chamber walls would surely explode.
the rifle came apart, and inspection revealed that it had not been incorrectly assembled, nor any apparent abnormalities.
well, if something won’t work the first time, try again. so, the rifle was put back together, and the experiment repeated. with the same result. time and again the rifle stripped the cartridge clear of the magazine, guided it into the chamber, and then the whole assembly stopped, just short of the cartridge entering the chamber enough to allow the bolt to close.
after repeated failures the rifle came apart again, and this time the cause was revealed, in the form of brass burnishing upon the face of the rim around the bolt, and upon the face of the lip of the extractor. taking the bolt apart, removing the extractor, and confirming that the bolt face was sufficiently milled to allow the cartridge face to fit within its confines confirmed my suspicions. the extractor was the culprit.
the extractor pivots on a pin driven through the bolt's shaft, and the face of it is pivoted downward relative to the face of the bolt, so that the lip fits snugly into the slot milled circumferentially in the cartridge case so that the empty cartridge is pulled from the gun’s chamber to cycle the action again after firing. well, absent a cartridge case to hold it back, the most forward part of the ejector was projecting too far into the face of the bolt, so far that as the bolt came forward pushing the case before it, the face of the cartridge was resting on a large flat at the front of the ejector, preventing the ejector from pivoting outwards, allowing the rim of the cartridge to slip under it, and move back to the blot face allowing the ejector to snap over the rim and hook it by the rim. the upshot of all of this was that the forward shoulders of the cartridge contacted the forward most dimension of the chamber, preventing it from going any further forward, resulting in the forward motion of the bolt being arrested.
the solution. well, if the face of the stone were about the same dimension as the face of the bolt, the outside of the cylindrical stone would be about the same circumference and curvature as the cartridge case, or so it stood to my reason. so, rummaging around in the parts bins, i found the stone, and proceeded to very gradually and very carefully relieve the flat spot on the fact of the extractor so that it would not prevent the rim of the case from sliding under it and allowing normal cycling of the gun’s actions.
i went very slowly at this, not wanting to weaken the strength of the ejector. it is a very small part, subject to enormous stresses, and it makes no sense to render the weapon inoperable by breakage by weakening a crucial part.
there are several lessons to be taken from all this.
first, never presume the operational reliability and function of even a well designed weapon, which the ar-15 rifle most assuredly is. the bolt and bolt carrier system whose weaknesses i have described above serves as the model for an entire generation of weapons systems adopted by the major military forces of the western world, including the germans and the english, no mere sticklers when it comes to weapons reliability.
second, remember the use of the weapon. it is just that, a weapon, and you have obtained it because of your belief that your life may depend upon its use, and its functioning when you may be forced to deploy it upon short notice and under great stress. you want it to work when you want it to work, as you life may depend upon it.
third, you may be placed in a situation someday when you have no choice but to rely upon your own devices. you should learn about the operation and function of your weapon of choice, and you should be capable of taking rudimentary steps at fixing and modifying it as the occasion may demand in order to get and keep the thing up and running. simple maintenance, such as keeping the machine clean and well oiled should be learned. disassembly and study to learn and understand the working and operations of the weapon in fact and theory should also be a priority: you cannot figure out how to repair or make something operate if you haven’t the slightest idea in the world how it functions. and, finally, you should not be averse to performing simple maintenance and repair on the weapon to make it work.
finally, firearms are complicated machines, and like all complicated machines, they have to be made correctly and in conformity with design specs, or they do not work correctly, and, as all machines, they can and do bread and require periodic maintenance and repair. you can be sure that i will watch the extractor for any signs of cracking while i still use it, and that it will be replaced with a part that does not require alteration to make the machine work.
the things i have described above do not rise to the level of genius, either in comprehension or mechanical skills. they do reflect, however, more that a superficial knowledge of the functioning of the weapon, and a willingness to learn about to keep them running and robust.
and, more than anything else, the things related reflect a basis understanding and comprehension of the importance of being familiar with the weapon and how it works, and the import tasks the weapon may be asked to undertake.
one wants the gun to function, as it is to function, when it is needed. there is no time to learn these things, to gain the needed knowledge and familiarity in a situation in which the gun has just refused to go boom, and you are faced by an adversary who has a heightened desire and motivation to kill you.
so, take you gun out, shoot it, and make sure it is reliable and functional, and functioning. perform maintenance and cleaning functions as though you life depended upon it.
because it does.
--john jay @ 06.05.2008
post script.
the m-4 variant of the m-16 military rifle is apparently susceptible to damage to the gas tube due to extreme heat during prolonged operation under automatic fire, this being caused by the very shortness of the carbine’s barrel, requiring that gas be bled from the hot propellant gases in the barrel very close to the receiver, where such gas is very, very hot, not yet having expanded into the length of the barrel and cooling.
i do not favor carbines in the ar-style rifle, finding a full length heavy barrel much more to my liking, as the heavier barrel is more accurate, and more suited to the style of use i envision in combating domestic terrorism. remember, i do not favor combat or fighting, the risk of being killed in such an endeavor far too likely to occur to inadequately trained civilians such as ourselves.
the m-4 is a close order combat variant of the ar-16 rifle, suitable for a style of combat any of us would have to be crazy to engage in at such frequency as to excuse recourse to the weapon. stick to a long barreled gun, as it has greater power, ranging and terminal performance due to increased bullet velocity. it gives a little more “stand off” capability, which i favor.
if you melt your gas tube, you have stayed far too long, fired far too many rounds of ammunition, and are quite likely about to die anyway given the environs in which the use of an ar-15 rifle might prove necessary.
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Posted by: star trek voyager | April 07, 2009 at 12:19 AM