Back story: Before my father passed away he gave me a SHITLOAD of parts kits. AK/ Krinkovs, MP34, Sten, Beretta (models 38/42 and the AR70!), Suomi, FAL, PM63, you get the idea. Lots more I can't even remember right now. So I wanted to build one of them into an operable gun and did a lot of research to see which one would be the easiest for someone who'd never "built" a gun. Research told me FAL is a fairly straightforward home build.
I sold every last one of those kits besides one of the FAL's. The upper was STG-58 (with a mint barrel) and the lower was Imbel. I bought a barrel vise and receiver wrench, pin gauges, Go/No Go gauges, and had to find the correct locking shoulder, for proper headspace. I got a complete kit of new springs from Falcon Arms. The receiver (on the FAL, the upper is the "gun") came from DSA, transferred to me through FFL, and yes I FA10'd it once I was done building. On the barrel, it had to be removed from the old torch-cut upper. That meant using a cut-off wheel VERY CAREFULLY and split the forward section of the receiver so it can be removed from the barrel threads without doing any damage. Then to time the barrel to the new receiver required repeatedly sanding down the face of the receiver, and mock-fitting the barrel until the barrel would tighten to the proper torque and be perfectly timed so the sights will line up top-dead-center.
So as far as difficulty goes, that part was the toughest and most time-consuming. When I was done and had a few months to shoot the rifle and make sure everything was good, I sold the barrel vise, receiver wrench, pin gauge set, and Go/No Go gauges and got a little less back than what I had spent on all that stuff.
Everything I learned while building that rifle I found on FALfiles.com, and this link:
Building the FAL at Home, Assembly
I don't remember exactly how much the whole project cost me in the end, but I want to say it was around $700. I have a folder somewhere with all the invoices for the receiver, parts and materials. Of course the parts kit being free was a big help.
The FAL has an adjustable gas system. On mine I had adjusted it so the brass lazily trickles out of the action and plops right down next to the rifle, with average 7.62 NATO at least. With hotter .308, brass would kick out with slightly more force but barely noticeable. None of the brass that I shot through my FAL was every overly beat-up. I ran out of factory .308/7.62 after I got my .308 Garand in a trade last year. I think I had around 300 rounds left of mixed Santa Barbara 7.62 and Federal .308, and I shot the hell out of the Garand when I first got it, giggling like a little girl and immediately in love with that rifle. LOL. So I have neglected my FAL since the Garand came along. But I just recently started reloading .308 and I worked up to a nice mild load that has so far run beautifully in my Garand, with decent accuracy. In fact on my lunch break today I'm gonna hit the range and run my reloads through the FAL for the first time. Since I can't afford to buy factory .308/7.62 for the foreseeable future anyhow, I'll be shooting nothing but reloads through both my FAL and Garand and want to have one load that will work nicely with both. When I get to the range today I'll first open up the gas adjustment 3 or 4 positions and start firing one round at a time from a magazine, and dialing the gas adjustment back up incrementally until the gun consistently locks open the bolt on the empty mag. My reloads are 43.0gr of H4895 under 150gr boat-tail bullets with mixed .308 and 7.62 brass, trim length 2.08 to 2.14.
TLDR: The FAL is a fun rifle.