An outstanding article I read on AR15.com (arfcom). It has no author, so I cannot give credit other than to AR15.com. I wanted to share it here with my fellow Canadians. The AR15.com site is predominantly american, so many of you may not venture there to find this. Its a great site nonetheless.
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AR15.com said:All right, after reading the 1000 th “I just found this site, and my friend has a Vulcan AR 15 for sale, is it a good deal” thread, I though about putting this together for the newbie. This is a compilation of a lot of the stuff I have learned from spending way too much time around here. Its also a lot of stuff I wish I had known before I started putting money into rifles. I am far from an expert, so if you see errors (in facts not opinions) please let me know. I also could use help with details on the different brands and what they offer. Please share your knowledge. I am still working on this and will edit as I have time:
So you want to buy an AR15:
First you should decide on what format you want, lets take it one piece at a time:
BARREL:
This is probably the most important decision you have to make, as it is the heart of the rifle.
Length:
The original M16 had a 20” long barrel. As the platform has evolved, all kinds of lengths have developed. The 20” barrel has some advantages- including greater velocity and longer sight radius than shorter barrels. The increased velocity is important if you are going to be shooting long range (say over 300-600 yards) or if you are going to be shooting at something which can shoot back at you. The latter is true because some military ammunition relies on fragmentation, (the bullet yawing and then breaking up inside the body) in order to cause damage and stop a person/animal. The faster the bullet is traveling, the farther out it will have enough velocity for the bullet to fragment. Look at the "Ammo Oracle" to learn more about this, as well as more than you could possibly ever remember about AR ammunition. The increased velocity has another advantage, in that the bullet will have a flatter trajectory, and thus hitting objects at unknown distance will be slightly easier, as errors in estimating the distance, or correcting for bullet drop or wind drift become slightly less important. The increased sight radius is useful, as it improves the shooter’s ability to shoot accurately. Because the front and rear sights are farther apart, any error in misalignment at the time of firing will be smaller as it is extrapolated out to the target. Note that the longer barrel is not more accurate, the sight radius simply makes it easier for the shooter to shoot accurately. This advantage disappears as soon as a telescopic or red dot sight is added to the equation. If you want to shoot at very long distances, for example long range target shooting, varmint hunting or sniping you might consider a 24” barrel. This increases your velocity, and adds to all of the advantages noted above except sight radius. Most 24” barrels use the same sight radius as the 20” rifle, unless they are specifically set up as a “race gun” for long range target shooting.
The next common shorter length is the 18”. I believe this length either evolved, or was made popular due to the SPR “Special Purpose Rifle” concept. The idea here is to have a rifle used by someone who is a better than average shot in a sniper type role, without going to a full blown sniper rifle. The goal is accuracy at long range, and the 18” is seen as a good compromise between the 14.5” M4 and the full 20” rifle.
The next common length is 16” which has evolved because of our laws in the US. The Army (feel free to correct me if I am wrong, I am not in the military, nor do I claim to be an expert on this) has decided that for the most part a shorter barrel is more useful. They have gone to the M4 which has a 14.5” long barrel. In the US it is illegal to own a rifle with a barrel shorter than 16” unless it is registered as a “short barreled rifle” which requires special paperwork and some extra $ to the .gov folks. Thus evolved the 16” barrel. The advantage to this is that you have a barrel which is handier to move around with, swings easier, is lighter, and you don’t have to register it and pay extra dough to the government. Probably the 16” is the most common length these days, most shooters having agreed with the army’s assessment that you don’t gain that much with the extra 4”, and the compromises are worth it to have a quicker handling gun. This is especially true for civilians who are not limited to FMJ ammo, and can select an ammunition which is not as dependent on fragmentation and velocity for self defense. It should be noted that the original 16” barrels used the “carbine length” gas system. This means that the distance from the chamber to the gas block (front sight base in most cases) on the 16” barrel is the same as what the military uses on a 14.5”. This distance is significantly shorter than the distance on a 20” barrel, because the gas pressure forcing the carrier and bolt backward only exists while the bullet is in the barrel. This pressure has to be present for a critical length of time, and thus with a shorter barrel, that time has to start sooner in the cycle. This results in a harsher recoil than one sees with a rifle length gas system, and potentially more problems with extracting the bullet from the chamber, as the rifle is now trying to do this while the pressure in the chamber is higher. The smart folks at Armalite came up with the idea of moving the gas system in the 16” rifle down the barrel a ways from where it would be on the 14.5” design, and they invented the “midlength gas system” (middy for short). This design is slightly easier on the components involved, as there is slightly less pressure in the chamber when the rifle is trying to extract the bullet, and there is less force transmitted to the carrier. This design also gives a slightly longer sight radius, and also allows the attachment of a normal designed ever important bayonet.
Obviously, the 14.5” is next. There is actually a way around the law noted above concerning SBRs that we should note here. If you attach an “extended” flash hider (Smith Vortex, SDI Extended A2, YHM Phantom, VLTOR Compensator, etc.) flash hider to the barrel in a “permanent” manner (for example by threading it on and then drilling a hole off center and driving a pin through it to keep someone from removing it) and the overall length of the combination is 16” or more, you have met the requirements. These barrels are usually referred to as 14.5” with pinned flash hiders. The down side to this is it makes things a little more difficult to remove the barrel and install most free float tubes, as with most the flash hider (FH) and front sight base (FSB) have to come off to install them. There are two piece free float rails which can be used to get around this as well. Again, the gains are maneuverability and portability, with the trade off of shorter sight radius and less muzzle velocity.
Once you get shorter than 14.5, you can go as far as you want. These rifles are designed mostly for shooting things in cramped quarters, and for easy maneuverability. The trade off is again lower velocity, and now significantly increased muzzle blast. These guns tend to be more particular about type of ammunition used, gas port location and size and need to be set up exactly right to run well. This is a fairly specialized area of ARs in my mind, and I have limited knowledge in this area so maybe someone else will come along to supplement my knowledge.
Material:
There are three common materials used in making barrels: 4140, 4150, and stainless steel (I believe 416 is the most common). Each has advantages and disadvantages. 4150 is the spec (as I understand it) for the military. There have also been discussions of 4150vs CMV which are over my head. Some companies use these terms interchangeably, and others do not, some will list their barrels as “4150 CMV“ while others will use one term or the other. In my mind these terms are interchangeable, but if someone wants to straighten me out, have at it Regardless, 4150 is apparently somewhat better than 4140 in standing up to the heat and abuse from full auto firing. I am not a metallurgist, but the folks who seem to know on page two say that the "40" vs. "50" has to do with an amount of carbon in the steel. More carbon gives a stronger steel, which is slightly harder to machine, but also more durable. The consensus seems to be that 4150 slightly better, slightly more expensive, and possibly a little harder to work with, but the differences may not be detectable in a rifle which is not used to shoot full auto.
Either of these materials can be chrome lined. Chrome lining is a process which bonds chrome to the inside of the chamber and or barrel in a very thin layer. This is advantageous in that the chrome lining is harder and has more “lubricity” or “slipperiness” than the underlying chrome moly steel (4140 or 4150). This extends the life of the barrel (possibly 2-3 times as long) as well as making it easier to clean. Some companies offer only chrome lined barrels, some offer both, and some offer only non chrome lined. The general consensus seems to be that chrome lining is easily worth the few extra dollars you pay for it. It does have one down side, however. The process of bonding the chrome to the inside of the barrel is not as exact as the process of cutting the barrel in the first place, thus overall chrome lined barrels are SLIGHTLY less accurate than non chrome lined barrels. This is a generalization (as evidenced by the impressive accuracy of the FN SPR series which usually shows incredible accuracy in spite of having a chrome lined barrel). Most shooters will never notice the decrease in accuracy seen due to chrome lining, but if you are that good, and it is that important to you, then think about getting a rifle without it. Many say that the amount of accuracy lost is less than or equal to ½” at 100 yards, so if you shoot Wolf like me, you will never see it.
The final common material is stainless steel. Again, this seems to be a material which become more popular due to competition as well as the REECE/ SPR/ DMR evolution. Most stainless barrels are designed for accuracy. Obviously the alloy of stainless is designed to be less susceptible to corrosion, something which the chrome lining of a chrome moly barrel offers, but without the downside of decreased accuracy. Stainless is not as corrosion resistant, nor as durable as chrome lining, but is used where one decides the trade off for better accuracy is worth it. As I pointed out above, most shooters will not benefit significantly form using stainless, as either they or their ammunition is not accurate to see the difference. There have been some recent threads about the durability of stainless which have been fairly impressive, and obviously it has been meeting the needs of the military for a while now, so if accuracy is your main concern, consider stainless. Stainless is not usually chrome lined, but there have been a few custom runs of chrome lined stainless.
How long do these materials last? Good question. I have seen numbers tossed around concerning a chrome lined barrel lasting around 20,000 rounds (lets see: $200 for 1000 rounds of wolf... ?$4000 worth of cheap ammo?). There was a thread by one of the industry sponsors outlining a SBR with a stainless Wilson barrel with 16,000 rounds through it which still had decent accuracy. A non chrome lined non stainless barrel is often said to last half as long as a chrome lined one. Remember, that the military definition of "accurate enough" is no where near the same as someone who shoots high power rifle, and regularly goes out to 600 or more yards. Also, you bumpfiring fools, or full auto guys will get less life out of a barrel because as the barrel heats up, it becomes more susceptible to wear by continued firing. Thus, YYMV (Your Yardage May Vary).
Profile
The profile of the barrel is the shape it was turned to on a lathe. This can range from a barrel designed specifically for accuracy which is 1” diameter, down to a “pencil barrel” which is designed to be light weight and handy to maneuver with. A great resource for learning about profiles can be found on Randall’s “AR15barrels.com” website here: Barrel Profiles. He shows all the common profiles, and I believe even has a chart showing differences in weights here: Barrel weight PDF link.
Of minor note. The finish used on most non stainless barrels is called “Parkerizing”. Some companies parkerize the barrel before placing the front sight base on, and some after, which results in much wringing of hands and slinging of mud when their respective fans (known affectionately as “kool aid drinkers) defend their favorite brand.
The barrel can be lightened further by adding "flutes" which are usually grooves added to a barrel to lighten it. This not only removes material to make the barrel lighter, but also increases surface area to assist in cooling the barrel. Occasionally you will see someone say that fluting a barrel will make it stronger. This is not true, as I understand it. The strength of a barrel is determined by its cross sectional area, and any time you remove material this will decrease. What you gain is lighter weight and more surface area.
Chamber First you have to know that there is 223 ammunition, and 5.56. The 5.56 is loaded to higher pressures for the military. When a barrel is manufactured the maker cuts the chamber he wants for it. A 223 chamber is slightly shorter in, and provides slightly more accuracy when used with 223 ammunition. This can cause a build up of too much pressure in the barrel if 5.56 ammunition is fired in a barrel with a 223 chamber. If you expect to shoot any kind of surplus ammo, you should make sure you buy a rifle with a barrel chambered to shoot it. This is slightly complicated by the "wylde" chamber. This is a compromise between the 223 and 5.56 chambers. It is intended to allow the user to fire 5.56 ammunition and yet improve on the accuracy of the 5.56 chamber. This is another option if you intend to shoot surplus ammo. Want to see the specs on different chambers? Go here: Link to AR15barrels tech page
Twist So, rifle barrels have "rifling" in them. These are lands (high spots) and grooves (low spots) which run the length of the barrel. The lands engage a bullet and give it spin as it travels down the barrel, just like a quarterback puts spin on a football. The rate at which the bullet spins is determined by its speed as it travels down the barrel, and the rate at which the lands twist in the barrel. The twist is listed as "one in x" were x is the number of inches the bullet must travel down the barrel to complete a single revolution. Early ARs had 1:12 twist (1 revolution every 12 inches). However, as bullet design evolved, bullets became heavier and longer. Longer, heavier projectiles require faster twists in order to stabilize them. If they do not spin fast enough, they wobble as they go downrange, and you lose accuracy. If all you want to do is launch 45 grain bullets at prairie dogs with your rifle, you can get away with a 1:12 twist. Actually, the 1:12 will probably work up to 55 grain bullets. Most ARs sold these days are 1:9 or faster twists. The 1:9 will stabilize 55-69 grain bullets, and may sometimes stabilize 75s depending on the rifle. A 1:8 or 1:7 will stabilize 77 grain and up bullets. This is important if you intend to shoot at very long ranges where the ballistic coefficient of these bullets is really needed, or if you want to shoot the heavier Black Hills or Hornady ammunition which performs near or at the top for self defense. You need to decide what you want to do with your rifle from the start so you know what twist you will need.
UPPER RECEIVER
The next thing to think about is the upper receiver. This is the piece of aluminum that the barrel threads into. The original design was the M16 which incorporated a “carry handle” with the rear sight mounted at the read of the handle. This was followed by the “A1” variant which incorporated the forward assist. The M16 and A1 rear sights require a “tool” (the tip of a bullet will suffice) in order to adjust windage, as a small pin must be pushed down in order to rotate the wheel which adjusts the sight. Many still prefer this design, as if one is involved in strenuous and harried activity he is not likely to inadvertently move the adjustment. In addition, this sight was not adjustable for elevation, as the adjustment for sighting in the rifle is made a the front sight post. The “A2” version is easier to adjust, requiring simply turning the windage knob, but also more likely to be accidentally moved out of place. In addition, it also incorporates a wheel which lies horizontally below the sight which allows adjustment for longer ranges by turning the wheel and thereby elevating the rear sight. The “A3” variant is called the “flat top” and is now probably the most common and most versatile. This has a mounting system milled into the top of the receiver which allows attachment of almost anything you could imagine- including a carry handle, optical sights, back up iron sights, or any air soft junk you could dream of. In my opinion, unless you are intending to spec out a rifle for a specific “look” there is little reason not to go with an A3 or flat top upper. The “M4 upper is similar to the A3, but it has “M4 cuts” milled into it. As I understand it, when firing full auto (particularly with a carbine length gas system) it is possible for the carrier to cycle quickly enough to try to strip a round from the top of the magazine before the magazine spring has had time to push the round fully up to be picked up. This results in the tip of the bullet jamming into the front of the receiver below the barrel’s feed ramps. The M4 cuts are basically a continuation of the barrel’s feed ramps which extend down into the upper receiver below the bottom edge of the barrel. They provide a slanted surface which helps start the tip of the bullet in the right direction. Again, this is primarily a concern if one is shooting full auto, and most would say that M4 feed ramps are not necessary on a semi gun, but this does not stop folks from spending hours extolling their virtues, or getting in heated arguments about them. Again, Randall has a good thread which shows pictures of these, and what you can and cannot do (basically don’t try to match up a barrel with rifle cuts with a receiver with M4 ramps and you won’t get into trouble) here is a link where you can see Randall's pics of the ramps.
FRONT SIGHT BASE
There is a lot of confusing info out there on this one. I think I have it right, but feel free to correct me if you know better. The front sight base (FSB) is an important part of the AR for several reasons: it serves as the home for the front sight (duh), but it also is the conduit through which the gas is bled off from the barrel to be directed back to the receiver to actuate the bolt and carrier group. In addition, if you don't have a free float rail, it holds the front of your handguards, as well as your front sling attachment. First of all, there are "cast" and "forged" front sight bases. The forged are superior in term of strength, and you will often see this advertised. The second issue is a little more subtle. Originally, the 20" barreled rifle used a front sight base which has a platform for the front sight post to thread into which is 1.94" above the top of the barrel. When the carbine came along, the distance between the rear sight and the front sight (sight radius) became shorter. This occasionally required the front sight post to be threaded farther out of the base to zero. Sometimes it would run out of acceptable amount of travel before zero was obtained. The initial solution was a taller front sight post. However, when the M4 carbine was created, the decision was made to give it a front sight base which was 1.98" above the barrel, and allow the rifle and barrel to use the same front post. These taller FSBs are usually (not always) marked with an "F" forward of the roll pin which holds the gas tube in. This is another selling point which you will see on uppers. For the most part, "forged F marked FSB" is how they are advertised. You will often see people say that the F marked base was designed for "flat top" uppers, but I do not believe this is correct for a couple of reasons. First of all, the resources I checked who seemed to know what they were talking about stated that is was a carbine vs. rifle thing, not a flat top vs. carry handle issue. Secondly, it is intuitive if you visualize the sight radius that a carbine may require a taller FSB. Draw yourself a picture showing a horizontal line through the rear sight, and the front sight. Then draw a second line showing the direction of the barrel. This line is angled up, so that the bullet travels upward and ultimately crosses the line of sight made by the front and rear sights. Now draw a second front sight base which lines up with the same line of sight, but with a shorter sight radius. You will see that the shorter radius requires a taller front sight position in order to achieve the same line of sight, as it is closer to the rear sight.
Because the FSB routes gas to the upper, and does it through the gas tube, the alignment of the FSB to the upper is very important. If you were to twist your FSB on the barrel, you could decrease the amount of gas going to the upper to actuate the carrier, or you could jam the gas tube in the carrier. Either of these could disable your rifle. Thus, pins are often used to fix the FSB into place so it is unable to rotate. Holes are drilled through the part of the FSB below the barrel, and these holes go through the lower part of the barrel. Two pins are then driven through both the FSB and the barrel. The only way to rotate the FSB is now to either shear these pins, or remove them. The "mil spec" is to use tapered pins. This means the pin (and hole) is not the same diameter all the way down, but is cone shaped. This allows a very snug, repeatable fit when you remove and reinstall the FSB. This is also more difficult to manufacture, so many folks use straight pins. Does this make a difference in the performance of the rifle? Only you can decide. It is very important if you decide to remove your FSB (for example to install a free float forend) that you know if you have taper pins, and you know which way to drive them. As an aside, I have removed a few straight pins, and bent some Craftsman punches doing it, so there is a surprising amount of force required to drive them out.
BOLT AND CARRIER
The bolt is the piece which picks up the cartridge from the magazine, pushes it into the chamber of the barrel, and then rotates to engage it’s teeth with the barrel extension. This contains the pressure from firing the cartridge in the chamber until it has decreased to a safe level. The bolt slides into the carrier, and is held there by the bolt cam pin. The cam pin slides back and forth in the carrier to rotate the bolt in order to engage the teeth as the carrier comes forward, and to disengage them as the carrier is pushed rearward. The bolt is the moving part on the gun which takes the most force, and is the most likely to break. For this reason, after spending most of your money on the barrel, the next place you might consider blowing a few extra bucks is on the bolt. You can increase your odds of getting a good long life out of your bolt by buying a good quality one. This gets into the differences between different brands of rifles and components, which we will eventually explore. Lets say that there was only one company in the world that made bolts, and they sold them to all the different manufacturers. You would assume that all manufacturers would have bolts of the same quality. However, this might not be the case. This is because you can do things to try to find problems with a bolt before it ever leaves your factory. You can fire a higher than normal pressure cartridge using the bolt, and then send it to be “MP inspected” (Magnetic Particle inspected). This means that a charge is place on the bolt and then it is surrounded by metal shavings. The bolt essentially becomes a magnet, and the shavings orient themselves around it. If there is a flaw in the manufacturing of the metal of the bolt, this produces a disturbance in the flow and therefore a disturbance in the pattern of the metal shavings. You can now reject the bolt as defective, and improve the overall reliability of your products. This is one of the main advantages you get from buying products from certain companies. Some companies MP test all of their barrels, some MP test some from each batch of barrels they make, and some don’t MP test any of them. The same is true of bolts and carriers. Obviously this whole process costs money, and thus the more quality control a company does, the more expensive their products become. Is the difference worth it? Well, if you spend your days in Iraq, it is clearly worth it, and you would be a fool not to buy the very best you could afford. If, like me, you spend your days desperately trying to hit that chipmunk which is running around your target 100 yards away it may not be. My goal in writing all of this is to provide information to people who don’t have a lot of background with the AR so that when they go shopping they can make informed and educated decisions, so decide what you need or want and what you can afford and then buy it.
Another term you will see in reference to bolts is "shot peened". As I understand it, this is pretty much just what it sounds like. The bolt is basted in a process very similar to sand or bead blasting, but instead tiny metal spheres are used. These impact the surface at a high speed and actually microscopically deform the metal. The result is like hammering the surface all over. This results in a bolt which has a very thin surface which is harder and more wear resistant without changing the underlying characteristics of the metal.
Of note, those smart people at Armalite have also figured out another way to increase the reliability of the bolt. They realized that because the extractor essentially takes the place of one of the bolt lugs, this creates a situation where the force on the bolt is not balanced. The two lugs next to the extractor take most of the force, because the bolt tilts under the strain from the pressure in the chamber. For this reason, these two lugs will almost always be the ones which fail. They figured out that if you shave down the lug directly opposite the extractor so it does not engage the barrel extension, you have again balanced the forces on the remaining lugs. The say that by doing this, they decrease the force on the two most susceptible lugs by 40% and dramatically increase reliability. They have, I believe, applied for a patent on this, so they are the only ones who do it.
Now to the lowly carrier. The carrier is not subjected to the same force as the bolt, and thus is not nearly as likely to break. The problem you see with carriers involves the extension which comes off the top (the carrier key). This engages the end of the gas tube. When the rifle is fired gas is bled off under pressure by the gas block (usually the FSB) and carried rearward by the gas tube. It is then directed into the key of the carrier to force the carrier rearward. Unfortunately the carrier key is held onto the carrier by two bolts. These can easily work loose from all of the constant slamming forward and backward which the carrier does. For this reason, after they are threaded in, the are “staked”. This means that they are struck with a punch or chisel in such a way that parts of metal from the carrier key are pushed into indentations made in the heads of the bolts themselves. This basically deforms and jams the two pieces of metal together in order to prevent the bolts from backing out. Here again is a source of hours of internet discussion concerning who does a better job staking than everyone else. Suffice it to say, when you pay more money for your carrier, one of the things you are paying for is someone who should know what he is doing, and has enough attention to detail to do this job right. This is also something you should inspect when you buy your new rifle to see that it was done correctly.
FIRE CONTROL GROUP (Hammer trigger sear)
Briefly, the standard trigger for an AR is a single stage. This means that you pull back until the hammer drops, without a significant change in the amount of force you need to apply as you pull back. This is a fairly simple and bomb proof design. However, if you really want to be as accurate as you can, you want to hold the rifle perfectly still as you pull the trigger. The more force it takes to move the trigger, the more difficult it is to hold the rifle still, thus other trigger designs were developed. The first to consider is a two stage trigger. This trigger has a small amount of travel which gets taken up with fairly light pressure, and then one hit’s the second stage of the trigger. Here the force required to move the trigger the remainder of the way to fire increases slightly. Essentially, you have applied much of the force and accomplished much of the travel of the trigger and you come to an easily recognizable spot in the pull when you know the hammer is about to come down with just a little more force. This allows you to most of the work in pulling the trigger and then focus on being perfectly still and have the best possible alignment of you sights before pulling the trigger. Probably the most common two stage trigger is made by Rock River Arms (RRA) and can be had for just under $90 on the Equipment Exchange (EE). These are fairly good, and can be tuned by a company called WOA to be even better. There have been some problems with them as they wear in- something involving one of the engagement angles and them going from a two stage to a single stage. Apparently this can be corrected by someone who knows what he is doing, but that’s all I can tell you about that. In addition, Bushmaster has I believe recently come out with a two stage trigger, and I believe LMT has as well. Another option is the Geiselle trigger, which costs considerably more (around $250), and is a bit more complex, but apparently has a great feel and is very high quality. Supposedly a lot of the high speed low drag (HSLD) guys are going with this trigger and it has a very good reputation. There is apparently also a new version of the Giselle according to ADCO which is about to be released which will be cheaper and simpler (still around $150 if I remember right). Also on the high end to consider are triggers by Jewel and Chip McCormick which can be adjusted to release the hammer with very little pressure on the trigger at all. The older McCormick had a reputation for doubling after a while, but supposedly they have now fixed this.
One thing to remember is that as you get more expensive, and more complex the chances of something going wrong increases. If you are running around in a combat zone you do not want a delicate target style trigger that can easily malfunction. The basic trigger is easily the most reliable, and you will find people who have had problems and malfunctions with pretty much all of the upgraded triggers. I have had great luck with having Bill Springfield tune the stock trigger to bring it down around 4 lbs with his $32 trigger job which can be found listed in the EE here. This is easily the best money I have ever spent on upgrading an AR.
So what about all these piston uppers?
In theory the piston upper is a great improvement to the AR design. The AR is one of few rifles which uses the "direct impingement" design. This means that gas is bled off under pressure from the barrel and sent back into the action to work the carrier. This design probably contributes significantly to the accuracy of the rifle, according to many, and keeps the weight down, but has some big downsides. One is the junk which comes with the gas. This causes fouling and carbon build up in the action where the critical moving parts are. In addition it places a lot of heat in this area as well. With a piston design, the gas vents under the handguards and is used to actuate a piston which in turn drives the carrier backward. This keeps the debris and heat which comes with the gas out of the inside of the upper, theoretically significantly improving the system. You hear some folks say that this is the solution to a problem that doesn't exist, but I'll bet if people had a choice between guns with each system and they were equal in reliability, accuracy, and in cost everyone would go for the piston. Apparently attempts to "upgrade" to a piston design have gone on for a long time. There was a drop in design around 20 years ago, which I cannot remember the name of, and there has been a company named ZM weapons making a piston design for quite a while but you don't hear much about them. Recently there has been a resurgence in interest in pistons. Patriot Ordinance ?Factory? (POF) has a design, as well as LWRC, and HK. Ares defense has a drop in modification as well. The POF must be purchased as a complete upper. I believe the LWRC can be installed by LW if you send your upper to them. The HK is for the military only right now (unless you have around $4000 for the one what was in the EE recently). I have seen a few problems noted with the POF design, and many with the Ares design. One of the main concerns is the force which is placed on the carrier key with these designs. This has to be very strong to avoid shearing.
As I said, the theory here is very good, the question is how does the execution work. There is no question that these systems will be cleaner to run, the concerns are reliability, accuracy and weight. We will see if these are the evolution of the AR, a temporary fad, or a small market which will parallel the main market at time goes on.
LOWER RECEIVER
There is a great thread concerning lowers that tells more than I will ever know, so go check it out: All about Lowers
STOCKS
I am not going to get into this too much, but here are a few basics. The original stock was the A1 version, and had a fixed length, and had a relatively short length of pull. The A2 is slightly longer. People usually have a preference of one over the other, so if you can try them both with all your gear on which you expect to use with your rifle and see which fits.
Adjustable stocks run the gamut from the simple and cheap to the sky’s the limit. One thing you need to be aware of is the different sizes of the “receiver extension”, or “buffer tube” which a telescoping stock slides over. There a “mil spec” diameter (which I believe is slightly smaller) and a “commercial” diameter. The threads on the two sizes are formed differently. On the “mil spec” the threads are apparently rolled into the tube, while on the commercial tubes they are cut in. Apparently, the former is superior. If this is important to you, make sure you get the “mil spec” version. I have seen this debated multiple times and have not seen the need to switch all my extensions yet, but I am sure someone will be along to make the case for the milspec version soon. To me the most important issue here is to make sure that the stock you buy is compatible with the extension you intend to use it with.
Good basic telescoping stocks include: RRA, Bushmaster, Stag, and others. More sophisticated versions are made by LMT, Vltor, Magpul, CAA and others. The best advice I can give here is try to get together with folks who have different versions and try them out, or if no one is around spend some time reading in the forums and asking questions.
FREE FLOAT AND RAILED HANDGUARDS
Probably the first question to ask yourself is do you really need one of these. If you want a vertical foregrip, or want to mount multiple things on your rifle you will want one of these to hang them on. Consider, however, that you are adding considerable weight to the rifle, and it is weight which is fairly far from your body. This will make the rifle handle much differently, and will add to fatigue when shooting for extended periods. However, the potential to be cooler than anyone else at the range, and to have more toys than all your friends is often irresistible, so here you go: All about free floats and rails
er the BM catalog carriers are MP inspected, not sure about bolts
