There has already been a lot of good advice given. However, until you tell us what you want to do with this rifle, we can’t really advise you. Best advice given so far is to come out and shoot with us. You can shoot FALs and ARs in different configurations until you find what you really want. Then go from there.
Before going too much further about the build, I need to ask some basic questions.
What is the primary intended purpose of this rifle? Plinking, home defense, a cool toy, a hunting tool, three-gun competition, all of the above?
At what ranges will you primarily be shooting this rifle?
Do you have any thoughts on optics?
I’ve never built an FAL or an AR upper. However, I have built several AR lowers and have researched complete FAL and AR upper builds.
The FAL build will be more difficult and generally requires more tools. Around here, many of us consider P806 the FAL build expert. If you have questions, he’s the man. Building an FAL will require “timing” the barrel. Attaching an AR barrel is a lot more straightforward.
Building a complete (upper and lower) AR requires some special tools, such as the barrel wrenches, vice blocks, etc. Building an AR lower is quite easy and requires few specialized tools. The only tools maybe not considered common are the roll-pin punches. You can do it without these punches, but they make the job much easier and help make sure you don’t mar the receiver. The razor blade “trick” chainshaw mentions is indeed the way to go. I’ve never lost a spring.
I think building the AR lower and purchasing a complete upper is really the way to go. Building an upper doesn’t really save you a lot of money, especially if you have to buy any of the special tools. If you know someone with the tools and knowledge, you will save some money. I just don’t think the few dollars you save is worth the time to build one and the opportunity to screw up something. Just my opinion.
I saved money by building lowers because I waited until I found good deals on the Equipment Exchange for things like buttstocks. If you buy a buttstock kit and lower parts kit from Bushmaster, you won’t save anything.
I only use RRA lower parts kits for my builds. I strongly agree with the advice to use quality parts. I also agree chrome-lined bores are preferable. However, depending on the rifle’s intended use, chrome lining might not be that big of a deal to you.
Many people have built rifles from kits and they seem very happy with them. Companies like Model 1 Sales, J&T Distributing and others offer kits, which include a completely assembled and head spaced upper, a lower parts kit and a buttstock assembly. It is everything you need, except the stripped lower. In fact, I am planning to build a kit gun in the near future to use as a “truck gun.” For some reason, I don’t have a problem leaving a kit AR in the car, but can’t imagine doing that with a complete Bushmaster or RRA. Maybe that says something.
Bottom line, if you’re just looking for something cheap to shoot at the range, a kit AR might be okay. If you want something that has a little better resale value and perhaps better quality, build a lower with RRA parts and buy a quality complete upper assembly.
If you want something with which you can tinker, go for the FAL.
Then again, if you really are just looking for something cheap to shoot at empty cans, an SKS might be just the thing. Plus, ammo is dirt-cheap.
Whatever you decide, we’re here to help you.