I recently received a question, and it’s one I get multiple times a week. The question was specifically about the pros and cons of rail systems. Instead of giving a short reply, I figured I would write up something a bit more encompassing to link back to. If you are looking for a rail, this might not answer all of your questions, but it should be a good start.
I’m going to make these suggestions based off my own experiences in the military, as a current city cop who deploys the rifle at least a few times a week, and as an instructor in a large department who gets a chance to deal with a lot of interesting variables in both training and operational aspects. These are my personal observations, they are what I relay to my friends and guys I deal without outside of just department training. These are the same suggestions I make to my military friends who come back from deployments and are looking to build their own AR15 to have at home, and for training outside that of what they get with the military.
Click the below picture to jump ahead for all the info wanted to know about rails, and maybe some things you haven’t thought about before.
To free float or not to free float. A “Free Floating” (FF) rail takes uneven pressure off the barrel and allows for a more accurate platform. Whether you need this or not is up to you. If you shoot using support, or like to wrap your sling, a free floating rail may make a large difference. Please note that a FF rail does not make the weapon more accurate, but it does allow the weapon to be more accurate. You shouldn’t expect your shooting ability to make a large jump just because of a rail. If you prone out and shoot 14-inch groups at 25 yards, its doubtful you are going to see a return on your FF investment. However, if you find that shooting off sand bags gets you different groups than when you are shooting prone unsupported, this could be your ticket. The other thing a FF rail does is eliminate any play in the rail system. Some guys hate any wobble or movement, especially with they are slapping a grip on their rail. A FF rail eliminates the play. A FF rail also permits zeroing of optics and lasers for precision work.
Lightweight is great, but it’s not the end all, be all. We don’t want a weapon to be unnecessarily heavy, but I’ll accept weight with the right trade offs. For example, my duty carbine would be lighter without my Aimpoint Comp M4 optic, but it’s not worth losing it because of the positive features it brings. My weapon would be lighter without a Gear Sector Handstop, but that works for both the push and pull method with the forward hand, and I use both depending on the tactics I’m using. I could dump the sling for max weight savings, but I don’t see that as realistic. You could save a few ounces going with a bare barrel instead of having a flash suppressor, but I chose to use a Battle Comp 2.0 because of how fast I can place rounds on a threat. All of those things are pretty straight forward, and guys grab onto them right away as common sense items. The next thing causes a bit of a switch in thinking.
Long rails versus short for max weight savings. This becomes the mother of all trade offs, but it really isn’t that hard for me personally once I go over pros and cons. First, lets think about why we are using a rail. Increased rigidity on the overall platform? That might sound like an odd one, but loose gear can get annoying, and I understand that. A creaking rattly car might be reliable, but doesn’t inspire confidence, and I think this becomes more apparent as guys rotate out of holding the magwell and move into shooting with their arm farther out. That also brings us into the idea of a longer rail to grasp it out farther, and there is no doubt that longer rail equals additional weight. Longer rails tend to also be a little more expensive. With this in mind, I would ask LEO reading this to keep a few things in mind. First, this is a weapon that is going to used to save your life, the life of your squad mates, and the live of those we serve. Secondly, this is a tax write off. Lets not forget for a minute that our profession expects us to make purchases, and this is a legit and easy write off, so make sure you save your receipts. Third, if you are buying higher quality gear, you are getting more for your money. It is also my belief that an AR15 purchased, or items purchased for it by a military member would be tax write off if you are using it to train and better your abilities for your career carrying a weapon. I’m not a tax guy, but I wrote off things when I was in the service with the blessings of my tax person. This leads us into the next section, so keep the longer rail idea in your head for another minute.
Barrel shadowing and you, and how to make room clearing a bit brighter. Think about the last time you cleared a room, whether in training or while you were kicking in doors and checking your corners for real. How much attention did you pay to your light? Typically it either works or it doesn’t, and when it doesn’t I switch to harsh language and my backup light. There is more to running a light properly than just fresh batteries, and there are some things that can help when you are mounting your light. A longer rail pushes your light out farther, which reduces barrel shadowing. A light mounted on a carbine rail tends to show some heavy shadow off the barrel. Take that same light and push it out farther on a longer rail, and you can eliminate that for a clean, even cone of light. Notice that none of the RIS II rails, like the short barreled MK18, are using regular carbine length rails anymore. One of the benefits of this is the better light spill they are getting from their weapon mounted lights.
Yes, the cheapest, fattest, heaviest free floating rails you can get “may” work. And they may even work for an extended period of time, but they also have the ability to come loose causing weapon failure. They have the strong possibility of having out of spec rail sections, not to mention the typical sharper edges. Think I’m wrong? Try working as an armorer for a large department or working as an instructor that sees a decent amount of AR15 range time and watch the junk that cops will bring in and try to get approved. Stop buying knockoff crap on ebay, my life is worth more than that and so is yours. If you want to take things off your carbine before you start training so they don’t get damaged, you need to be pimp slapped (twice).
With the right rails, you can get a longer rail that is lighter than many of the cheaper offerings. You will typically pay more for higher quality rails, but the development and increased machine time typically yields a smoother, better machined, lighter rail of higher quality. The longer the rail spends on a CNC machine, the higher the cost. Additional CNC machine time translates out to higher cost to the manufacturer, which obviously gets passed along to the dealer and consumer.
Do you need anti-rotation devices? Many of the free float rails on the market incorporate some form of anti-rotational feature. These can come in many forms, with some looking like a bolted on cheap after thought, and others looking like the seamless design that they were. However, they all work on the same basic principle, which is that if your rail starts to come loose, your barrel is starting to come loose and things are starting to turn very ugly. I’ll point out that a properly installed high quality rail should not find itself coming loose, but a mechanical block in the form of an anti-rotation piece is cheap insurance.
Do I want a one piece or a two piece rail? I don’t know, do you ever plan to clean the barrel under the rail? Most of the two piece rails are pretty straight forward when it comes to removing the bottom rail for cleaning, though it may still require an allen wrench in some cases. Installation of a two piece rail is usually easier, and you most likely won’t need to pull the barrel nut to install a two piece rail. A one piece rail typically requires that you remove the barrel nut, which may be more than someone with a casual skill set wants to take on. Its been commented that a one piece rail is usually stronger, but I’ve never heard of a quality two piece rail being broken unless its something like a weapon being run over. I own both, and use a two piece FF rail currently on my duty weapon.
Folding sights and covering the gas block looks cool, but do you really need it? This is kind of like asking what type of girl (or guy on the chance the fairer sex is reading this) you find attractive. There are pros and cons to each, but it comes down to what you like best for your own needs. A fixed front sight base (FSB) is most common on modern M4s, but if we look at the next generation of M4s in the form of the RIS II, or weapons like the SCAR, we find folding sights are the new norm. A part of this switch is that fixed sights were installed on the M16 because there were no electronic options for sights at time of its development. It wasn’t until the M4 that we saw mainstream acceptance of the Aimpoint within the military. The rear sight was made to fold out of the way for a cleaner view through the optic. With modern optics, the reliability is high enough that having a front sight sticking up all the time is something you may or may not be need. I don’t advocate eliminating iron sights by any stretch, but by going with a longer rail and covering the gas block and front sight base, we are able to get a longer rail. The longer rail space is a blessing not only for mounting equipment, but for some of the more modern shooting techniques in which the forward hand extends out more. The need for the longer rail can be debated, but guys using the MK18 have been using a longer rail and shorter barrel than the M4 users for quite awhile, and I don’t see any of them wanting to switch back.
