The first time you finish an AR 15 80% lower receiver you get this feeling of accomplishment and joy. I did it, this is mine, and I made it. I didn’t even scratch the finish. Alrighty, you now have your lower receiver, where do we go from here? Your overall goal is to finish your build, but your next goal should be to fill that lower receiver with all the parts it needs to grow into a full sized AR 15.
The Must-Have Components for your AR 15
Lower Parts Kit
A Lower parts kit contains all the necessary good to complete your AR 15 lower receiver. This includes a very wide variety of parts. The following are all required to form a complete lower receiver.
Miscellaneous Small Parts
These small parts include all the necessary springs and pins to complete your AR lower receiver. They are included with any basics lower parts kit. Their primary function is to hold the lower receiver together.
Trigger and Fire control Group
A trigger and for control group are several parts that allow the trigger to be pulled, and the hammer to fall. Trigger kits can be one piece drop in units or pieces that require the user to fully build and install. The complete fire control group includes.
Two control pins to hold it all together.
Often known as the selector, this is the device that allows the user to swap from safe to fire. This part can be a ’short’ throw variant, or an ambidextrous or left hand only variant. Included in an LPK.
The bolt catch acts as a break for the bolt when the magazine is empty. The follower in the empty magazine will lift the bolt catch and stops the bolt. Bolt catch will also allow to manually send the bolt home, or manually lock the bolt to the rear of the weapon. Is included in an LPK.
The magazine release is a small button on the side of the receiver. It releases the magazine from the weapon. Magazine releases can vary in size and style to suit the user. Is included in an LPK.
Buffer / Buffer Spring / Buffer Tube
These three parts must match for your rifle to function correctly. The buffer slows down the bolt and reduces felt recoil from the weapon. There are four different weights and the heaviest weight that will function in the rifle should be used. Calibers other than 5.56/223 may also have an effect on your choice of buffer.
The Buffer Spring returns the buffer to its original position and aids in pushing the bolt forward. The size of the spring is determined by buffer tube. The Buffer tube houses the buffer and spring and determines what kind of stock you use. A full-length A2 buffer tube will house a fixed rifle stock, a carbine length will accommodate a collapsible stock, and a pistol length will not accommodate a stock. Springs come in rifle, carbine, and pistol length and will accommodate their respective tubes.
The pistol grip makes comfortable shooting on the AR possible and houses an important spring that allows the safety to function. There are a wide variety of different grips for different hands available, and LPK’s typically come with one.
The stock allows the shooter to maintain a stable platform while shooting a rifle. The stock fits over the buffer tube. There are a wide variety of stocks available to accommodate different shooters. Stocks can be collapsible or fixed.
Bullet Button (CA residents only)
A bullet button replaces a typical magazine release and necessitates a tool to release the magazine. California requires this on traditional AR 15s to avoid making ‘assault’ weapons.
That will fill your Lower receiver, to complete the top half of your gun, you’ll need the following.
Like the lower receiver, the upper acts as the housing for all the parts necessary to make the weapon function. The small notch behind the ejection port prevents brass from hitting the shooter.
Upper Receiver Miscellaneous Small Parts
Like the lower receiver, there are a variety of small parts necessary to complete the weapon.
A forward assist allows the user to manually shove the bolt home. Occasionally a dirty AR 15 may have issues with the bolt going full home or the user may need to silently load an AR 15.
Ejection Port Cover
The ejection port cover is to protect the insides of the weapon from dirt and debris when not in use.
Bolt Carrier Group
The bolt carrier group holds the bolt, firing pin, and gas key. It performs the necessary function to fire the weapon and extract and eject the empty case. It also resets the hammer. BCGs come in a variety of different finishes for different performance levels.
The charging handle fits over the bolt and facilitates manually loading the weapon and pulling the bolt to the rear of the upper receiver.
The Barrel stabilizes the pressure from the round and is rifled to spin the bullet. You can select your twist rate to stabilize different weight projectiles. Available in a variety of sizes.
The barrel nut ensures the barrel is secured to the upper receiver.
The gas block intercepts the gas created by burning powder and sends it down the gas tube. The gas block can also be a combined front sight.
The gas tube takes the gas intercepted by the gas block and allows sends it rearward to cycle the bolt. Gas tubes come in different sizes to match different size weapons.
Handguards protect your hands from the heat of the barrel and give you something to grip with the forward when firing the rifle. If you are using Non-free float handguards, like keymod or MLOK you’ll also need a;
- Delta Ring Assembly
- Handguard Cap
Once your AR is built and you have a functional gun you can look at accessorizing. You can go crazy here and Barbie doll your rifle to high heaven. There are three accessories I always suggest.
A good set of sights made by a reputable company will ensure you can hit your target. Magpul, Yankee Hill, LPA, Troy, and tons of others make excellent sights for AR 15 rifles.
For hunters, a sling is absolutely necessary. It makes climbing, ducking, or crawling possible. A good sling will bear the weight of your weapon well, and actually, make it easier to shoot.
I always recommend having a few extra mags laying around. This ensures that if one breaks you have a go to. Also, some states require magazine limits, or limits when hunting. Magazines are affordable, and a worthwhile investment.DISCLAIMER: If you are new to the world of DIY AR-15 building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. We are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.