Firearms Stack Exchange Archive

Building AR-15 from kit

I’m looking at building an AR-15 from a kit plus a stripped lower receiver, both ordered online. I know nothing about guns, this will be my first firearm (I’ve looked and it’s legal in my state). Is this crazy? I’m assuming I can just assemble it, get some ammunition and it should be fine right?

Answer 1007

Ok... where to begin. You have a couple questions here, and many implied questions as well.

The Lower Receiver & Kit:

Lets start with the "kit". What kind is it? Where did you order it from (links would be good)? Typically, when you build an AR, you look at an upper receiver and lower receiver. You will need a lower parts kit (sometimes called an LPK). It contains the small components that fit into the trigger assembly and lower receiver (Safety, etc), and you will definitely need it. Here is one from a reputable seller online:

http://palmettostatearmory.com/index.php/palmetto-state-armory-gen-2-moe-lpk.html LPK from Palmetto State Armory retailer

That covers most of the Lower Receiver. I'm glossing over a lot here, but the basics hold.


The Upper Receiver:

Familiarize yourself with the Bolt Carrier Group and upper receiver portions of your AR. AR's come in two variants: Piston-driven and Direct Impingement (sometimes called "DI"). Essentially, the two differ in how to handle the hot gas that your gun uses when it discharges a cartridge. Without complicating things further in this thread, here is a quick and short video showing how the two operate: http://www.youtube.com/watch?v=M7GTZ0DixqA

This sort of information (knowing your Lower, Upper, LPK and DI or Piston) are sort of the basics you'll need to know at some point. The most common AR build is chambered in 5.56/.223 Rem. I've seen some that are 7.62/.308 Win as well. Your's is likely .223 or 5.56.

Before you even consider firing a round in the rifle, make sure you know the gun inside and out (you'll have to know most of it, since you'll be assembling it). Not all uppers can fire 5.56 NATO cartridges when they are stamped .223 Remington. This is due to the pressure differences the rifle will undergo on a 5.56 NATO cartridge vs the .223 Remington round. However, if your rifle is stamped for 5.56 you can shoot any .223 and not have to worry. I could go off on a tangent about the Throat leade in a .223 vs 5.56 rifle, but I'll refer you to this article first: http://www.freerepublic.com/focus/f-news/2677734/posts

Suffice to say, stick with whatever ammunition your upper tells you to use. Read the manual :-).

Finally, I learned most of what I know by browsing the forums of a well respected gun-community called CalGuns (http://www.calguns.net/calgunforum/index.php). There are tons of "how tos" posted there, as well as deep information on ARs, components, parts, etc. I'll plug them here since they've been a positive force in the gun ownership community, and taught me basically everything I know.

I wouldn't recommend building an AR from scratch if this is your first gun. Don't get me wrong, they're great rifles and work well when properly maintained, but to have never owned a gun and jump into it by building an AR might be a bit overwhelming, and you do not want to make mistakes. If you can, friend a local gun shop (buy your ammo from them or any accessories, the AR is the barbie doll of the gun world, with a million and one useless accessories ;-)). Friend the gun shop, then go in and discuss your AR, questions you have, etc. If it's a good shop, they'll help you out because they realize you'll be in later to buy items for it.

Hopefully this helps, and congratulations on becoming a gun owner!

Answer 1010

About the only thing that can go wrong (and it very rarely will) in an AR build is headspace. The reason in can go wrong is because headspace is a function of the bolt and barrel (actually barrel, with barrel extension - the part the bolt locks into). Modern manufacturing is accurate enough the under normal circumstances a new bolt will fit a new barrel correctly, but there is no guarantee. Any of the firearms parts companies (Brownell’s, Midway, Numrich, etc) will have go / no-go gauges you can use to test your assembly.

Assembling your own AR can be fun but it is also likely to be more expensive than buying an assembled rifle, so if you’re looking to save money, it’s not the right way to go.

Answer 1013

Make sure you have a few punches, (preferably brass) pliers and electric tape. You’ll need a torque wrench and you may want to consider an “Upper Vise Block” if you’re installing your own barrel. Assembling the lower is pretty simple. You can find some good resources at AR15.com especially here. Headspace can be a concern if you’re completely assembling the upper from various parts, but a good upper kit will already be headspaced to either .223 or 5.56. (See previous discussions on ammunition compatibility here.) and headspace is really set by the bolt and chamber being cut to spec. Buying as a kit will make assembly a lot easier, the only thing you really need to worry about is matching your buffer to your gas tube (and it’s not too hard. Full length rifle/gas tube = rifle buffer and rifle buffer tube, carbine length = carbine buffer and carbine stock tube) Make sure you perform a “Function Check” when you’re done assembling.

Answer 1078

An easy first step if you plan to have more than one AR15 is to buy a complete upper and build your lower from a lower parts kit and a stripped lower. I did this with my first AR several years ago. I’m working on a second AR now. I have a stripped lower and the lower parts kit is on the way. I’m still debating whether or not I will build the upper or buy another complete upper.

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