Your Custom AR-15 Build
With the amount of cheap AR-15 parts available on the market, it’s become extremely easy and cheap to build an AR-15 rifle. This is great for anyone who wants to own a custom AR-15 built rifle without paying the high price of buying a completely custom-built AR-15.
For those who are new to owning an AR-15 rifle or who have never built one, for themselves. The task of knowing what to buy, what you need, and where’s the best place to spend your money on your custom AR-15 build. There are so many manufacturers selling AR-15 parts, it’s hard to know what is worth the extra money or what is just overpriced and unnecessary. As you read on you will learn what parts to spend extra on and what cheap AR-15 parts you can buy without worry.
Tools Needed to Build Your Custom AR-15
Before you plan on picking parts for your custom AR-15 build you need to make sure you have a few tools to make the build easier. Brownells has great videos on how to build an AR-15 and the tools you need.
They get very specific on what each tool is used for. While they are correct on everything. A few of these tools are more for ease of installation as opposed to being a necessity. When it comes to building a custom AR-15 on the cheap it is possible to get your rifles assembled without all of these tools. Here’s the list of tools you’ll definitely want to have to assemble your custom AR-15 build:
Must-Have Tools
- A set of small punches
- Roll Pin Punches
- A plastic or brass mallet
- Barrel Wrench if you building your own upper
- A Torque Wrench (if installing your own barrel)
- Small knife or small flat head screwdriver
- Access to books, or YouTube
Nice to Have Tools
- Vise
- Armor’s Lower Receiver Block
- Armor’s Upper Receiver Block
- Various Wrenches
- Allen Wrenches
Parts of an AR 15
When you look at a parts diagram of an AR-15 it looks very complicated. It’s not as bad as it looks. There are lots of little springs and other pieces. However, when you get down to putting together your AR-15 it won’t be as hard as it looks. Putting together a custom AR-15 build isn’t as hard as it looks.
Build an Upper
Building an AR-15 upper takes a little bit more care than when you put together the lower. However, it’s not as precise as most rifles because Eugene Stoner designed it to have interchangeable bolt carrier groups and be easily re-barreled without a lot of work.
Stripped Upper
The stripped upper is where you can save some money on your custom AR-15 build. You can buy the cheapest stripped upper you can find from a reputable company and be fine. Most uppers are manufactured by a few companies that put different names on them.
While you can buy beautiful billet uppers, or matched upper and lower receivers. They aren’t necessary for your gun to function well, or last a long time.
The only thing to consider with a custom AR-15 build. Does your stripped upper comes with the dust cover and forward assist pre-installed. The kit for the dust cover and forward assist is only $15. So this is a matter of time more than saving money.
Barrel
The barrel is one of the most important components of your custom AR-15 build. Do not go cheap on the barrel. There are a few basic things to consider when looking at barrels. The style of barrel and the twist rate are the most important. What caliber it’s rated for and the length are things to consider also, not to mention gas system length.
Barrel Profile
The style of barrel is really the most important thing to consider. The generally on barrels you have three basic options for the profile.
The gunner profile barrel or pencil barrel gives you a lightweight barrel saving you weight on your rifle. The downside to these barrels is that they can get warm if you shoot too many rounds too quickly. When they get hot they can warp slightly. Which in turn can throw off your aim and affect your rifle’s accuracy. This especially true on cheap barrels.
Next is the HBAR profile. This is a heavier profiled barrel that has some change in the diameter of the barrel past the gas block. For the most part, it’s a thick straight barrel. This extra thickness gives the barrel the ability to handle faster shooting and more shoots without any deflection of the barrel. With all the extra metal it takes more shooting to heat up the barrel. Of course, they are heavier so it will add weight to your gun, but nothing like a full-on heavy barrel or bull barrel. The HBAR is pretty much the great compromise on barrel profiles.
The heavy barrel, better known as a bull barrel is designed to be extremely accurate. With the barrel being the same diameter the whole length. This gives you plenty of material to dissipate heat and keep the barrel from flexing. Sometimes these barrels are fluted. These grooves are cut into them the length of the barrel to relieve possible stress points and reduce weight. They are the most accurate barrels you can get.
Twist Rate
The twist rate of a barrel is simply how tight the rifling is in the barrel. So a 1:9 means that the rifling makes one whole twist in 9″ of barrel. This is important because it tells you how fast the bullet will be spinning when it leaves the end of the barrel. As a general rule of thumb, heavier bullets require a faster twist rate to stabilize the bullet. Think of it like a football. The faster you spiral the football when you throw it the straighter it flys.
If you want to know more about twist rate, Pew Pew Tactical does a good job of explaining. As a rule of thumb the heavier the bullet you want to shoot the faster the twist rate you’ll want in your barrel, and likewise, if you want to shoot light bullets you’ll want a slower twist rate.
Flash Hider/ Compensator
Since most AR-15 barrels come threaded at the end you’ll need either a flash hider or compensator (muzzle brake) to protect the threads. There are lots of different style flash hiders. Heck SeaHag Munitions even sells one that looks like a hog head on the end of your gun. However, a simples A2 style flash hider is the cheapest and honestly all you need.
Compensators can help eliminate felt recoil. They are loud to anyone shooting next to you. They bounce sound off ceilings and walls around you. The benefit from the reduction of recoil is more than made up for by the extra noise to everyone around you.
Barrel Length
Barrel length is required by law to be a minimum of 16″. However, you can go longer. The longer the barrel the more accuracy and speed of bullet you’ll get, to a point. There are lots of trade-offs on the length. If you are concerned do some research. Most likely you’ll either get a 16″ barrel or if you want to do long range shooting with accuracy get a 20″ barrel.
Gas System Length
The gas system length, you don’t really get a choice on. The barrel length dictates the gas system length. If you do happen to get a choose the gas system length. The longer the gas system the lighter the felt recoil will be.
Caliber
The most common barrels for an AR-15 are .223 or 5.56 and there is a difference between them. If you want to understand all of its differences The Truth About Guns has a great article explaining them. What you really need to know is that the best bang for the buck is to either buy a .233 Wylde barrel or a 5.56 barrel. Either one of these barrels will let you shoot both .233 and 5.56 rounds. This option can save you money on ammo.
Handguard
Your handguard is another place you can save money on your custom AR-15 build. It’s best if you get a handguard that free-floats your barrel, one that only attaches to the barrel nut. Make sure you check the length of your handguard and match it to your barrel length. So, don’t buy a 17″ handguard for a 16″ barrel. Likewise, buying a 13″ handguard for a 24″ barrel will look a little funny.
A handguard that has a rail the full length so you can mount any type of optic on your rail, is pretty nice. If you want iron sights it will be a necessity to be able to mount the front post as far out as possible. The other nice thing is for it to have some sort of mounting system built into it. This will be either a keymod or M-lok style. That’s a personal choice on which works for you, and the accessories you want to mount to your rifle.
There are all sorts of places to buy handguards. However, I’ll admit I love the ultralight slim keymod handguard from 223HandGuard. If you have bigger hands this might not be to your liking. You’ll have to find a handguard that works for what you want from your custom AR-15 build. Just remember the handguard doesn’t have to expensive it’s just there to keep your hand off a hot barrel.
Bolt Carrier Group
Your Bolt Carrier Group (BCG) is another place you can save money on your AR-15 custom build. Most of BCG’s are the same. The biggest differences are full-auto and standard with a few being ultra-lightweight. You’ll want to buy a full-auto BCG. They are slightly heavier and stronger. A Full Auto BCG won’t turn your AR into a full-auto nor are they illegal to have in your rifle.
There are plenty of different coatings for BCG’s. The standard Mil-Spec is a phosphate. It works and you’ll never have any major problems. They are also the cheapest.
However, there are lots of other coatings that claim to be longer-lasting and easier to clean. It’s my experience that the only thing that really makes a BCG easier to clean is a smooth surface. This is where a Nitride coating is really nice. It’s a smoother finish and holds up better. Plus you can usually still find a Nitrided BCG for around $100 or less. Well worth the money. Other coatings like Nickel Boron and Titanium Nitride add a lot of extra expense without adding an equal amount of function. They do look nice and shiny though.
Misc AR-15 Upper Parts
The last couple of things you’ll need to complete your upper is a gas block, gas tube, and charging handle. Make sure your gas tube length matches your barrel. Your charging handle is a personal preference, buy cheap if you want. If you plan on having a left-handed person shoot your rifle look into spending a little extra on an ambidextrous handle. If you have larger hands an extended handle may be a good idea.
As far as your gas block, make sure it matches your handguard. If your handguard is going to go over your gas block you’ll need a low profile gas block. You can buy an adjustable gas block but most of the time you don’t need it.
To save yourself a huge headache later make sure whatever gas block you buy it’s made of steel. They sell aluminum gas blocks for cheap. These are bad. Aluminum expands at a different rate than steel so as your barrel and gas block heat up during shooting the block can get let gases bypass your gas tube causing cycling issues.
Buy a Complete Upper
The easiest way to build a custom AR-15 is to buy the upper already completely built. That way you don’t have to install the barrel, handguard, or anything. Just put it on top of your lower and you’re done.
If you do choose to buy a complete upper there are a few things to consider. First, you can buy them online and have them shipped directly to your door.
You’ll still need to look at the barrel first. Just like with choosing a barrel you have to look at the barrel on a complete upper. Many of the complete uppers have cheap pencil barrels and really expensive handguards. Which do look nice, but don’t play much into how the rifle shoots. The whole reason for a custom AR build is so you can have a nice shooting rifle. If you just wanted a good looking rifle you’d buy a complete custom AR-15 for whatever it costs.
The last thing to look at when you start looking at complete uppers is, do they come with the BCG? This will change the overall cost of an upper. Most places like Palmetto State Armory and Brownells don’t always sell the complete upper with the BCG. So when pricing out a complete upper remember you’ll have to add in the cost of a BCG.
Complete Lower
Once you have your upper you’ll need a lower to attach it to. The cheapest way to get a lower is to buy a complete lower. The downfall is that the lower is considered by the ATF to be the firearm. Thus you need a background check to buy it and it must be shipped to an FFL dealer if purchased online. Which means it may be cheaper to buy the lower locally. Especially if you are buying a stripper lower.
That all said, you can pick a complete lower from Palmetto State Armory with Magpul buttstock and grip. This is a good deal as you will spend more than that on a lower parts kit, buffer tube, springs, buttstock, and stripped lower most days.
In fact that only reason to put together a stripped lower is because you want a better trigger than basic mil-spec. At which point you will have more money into your lower, but it will be a more customized AR-15 build. Not to mention it will save you from replacing parts on your rifle in the future when you want to upgrade your trigger or maybe your buttstock.
Stripped Lower
If you decide to build your own stripped lower instead of buying a complete one, the best place to buy a stripped lower locally. Most times when you add shipping and FFL transfer fees you won’t save a lot of money compared to buying one online. Of course, there are some pretty cool stripped lowers that aren’t always available locally. You’ll have to decide what you want to spend your money on. Anything above a basic stripped lower isn’t a necessity.
If you are just looking for a simple lower. Remember many lowers are made in the same place with different companies logos stamped on them. Unless you are buying a custom lower or a billet lower any metal stripped lower will work.
Lower Parts Kit
What comes in a lower parts kit (LPK) really depends on what you need. If you plan on putting in a custom trigger group, buy an LPK without the trigger group. If you don’t care about a Mil-Spec trigger or you want to polish your own trigger group. Buy the LPK with everything in it. Some will come with buffer tube spring, and buffer, along with the furniture. Other kits will only come the springs, detents and trigger group. It’s all a matter of how much you want to bundle together to save a few dollars and the quality of lower parts you want.
The biggest thing to think about with an LPK is making sure you don’t end up buying the same thing more than once. So if you want a custom trigger don’t buy an LPK with a trigger group included.
Trigger Group
The trigger group is where you really start to customize your AR build. There are lots of companies that make trigger groups for the AR-15. Manufactures like Geissele, Hiperfire, Timney offer lots of options. From 2 stage triggers with a slightly higher trigger pull on the first stage and very lightweight breakpoint are very common. Some of these two-stage triggers are 3 lbs and 1.5 lbs for the second stage. There are also single-stage triggers with 3.5 lbs trigger pull weight.
When it comes to buying a trigger for your custom AR build you have to decide if you want a really nice smooth light trigger or is a heavier mil-spec trigger ok. The smoother and lighter your trigger is the more it will cost.
Many of the better triggers come as what is called a drop-in. All you have to do is drop them in and line up the pins. Whereas mil-spec triggers require you to get all the springs and pieces installed in just the right order.
If you are building on a tight budget your trigger group can easily double the cost of your lower build. So consider that. It may be worth your time to polish a cheap trigger group and buy lighter springs. Although it won’t have the feel of a $200 trigger group it will work and save you lots of money.
Furniture
The buttstock and pistol grip are referred to as furniture. While any old mil-spec grip will work the Magpul pistol grips are far more comfortable. For the $20 you can have a nice pistol grip. If you think you’ll have different people shooting your rifle or you want to have different size back straps for your grip Magpul sells a pistol grip that has interchangeable backstraps and a holder for your gun oil for under $40.
When choosing a buttstock yet again it’s a matter of preference. Although if you plan on doing any long-range shooting you may want to choose one with a wider comb for a better cheek weld.
The other thing to remember is that you need to match your buttstock with your buffer tube. Just make sure you get your buttstock and buffer tube in the same size. The best option is to buy them as a set.
Buffer Tube, buffer, and spring
The buffer tube, buffer, and spring is pretty much the last thing you need to complete your custom AR build. If you haven’t bought them in a set with your lower parts kit, or buttstock, you’ll have to buy them separately. There are two different sizes of buffer tubes. Mil-Spec and Commercial. Commercial buffer tubes are larger in diameter. As far as which one is better that’s been a huge debate for a long time. The truth is neither one is better than the other, they are just different. Sort of like the difference between metric and standard measurements.
As far as buffers and springs, they make different weighted buffers. For the most part, you don’t have to concern yourself on the different buffer weights. It’s best to just buy the tube spring and buffer in a set and don’t worry. The main reason to have different buffer weights is to control the rate at which the BCG cycles. Unless you are custom loading your ammo a standard one will normally work just fine.
80% Lowers
Recently it’s become popular for people to buy what is called an 80% lower. These are stripped AR lowers that are only machined to 80% completion. This means they are not considered a legal firearm by the ATF. This is because you can’t drop a trigger into them without machining them. This also means you can buy them and finish them yourself without having to go through an FFL transfer or background check.
While this sounds like a great hassle-free way to build a gun. There is no way to save money on your custom AR build. The 80% lowers are usually about the same price as a full stripped lower. Plus you have to buy a jig and tools to complete the 80% lower. This raises the price of the lower to almost double the cost, not including your time to finish them off.
Final Thoughts
When building a custom AR on the cheap, it’s all about where you can save money and where you need to spend money. Your barrel, trigger group, and to some extent furniture is where you want to make sure you get good quality that fits what you need. The stripped lowers, and stripped uppers is a great place to save money.
Although this would seem counter-intuitive as you want a good strong base for your rifle. The lower and uppers and only really hold the other parts of your rifle. Spending extra on billet matched upper and lowers isn’t necessary. Nor will it make your rifle that much better. Compared to the extra cost. Just like spending extra on parts kits and even custom dust covers, or special flash hiders. These are all things that will add to the cost of your gun but not really add functionality.
If you are on a really tight budget for you custom AR-15 don’t forget to add in the cost of some sort of sights. It would be a shame to spend all your time and effort building the perfect AR-15 just to realize you have not money left over to buy sights. Whether you are buying a scope, a red dot sight or a plain set of irons sights, make sure you budget for some way of aiming your rifle.