A few days ago I bought a stripped AR-15 lower online from Palmetto State Armory when they went on sale for $49.99 plus $7 FFL shipping. I've never built an AR-15, but I've been wanting to for a long time, and knew I had to buy since the price was right. I've been doing a lot of reading online and watching videos on building your own, but still have a few questions. I want to build a decent quality, all-around good rifle. From my reading, here's what I think I want: - 16" barrel, non-fluted, chrome-lined, 4150 - M4 extended feed ramp cuts - chambered in 5.56 NATO - 6-position adjustable stock, mil-spec buffer tube - forged front sight base, f-marked, parkerized, tapered pins - MP tested, pressure tested, shot-peened bolt - flat-top upper receiver, T-marks on rail - staked gas keys - non-staked castle nut (I've heard it's not a big deal and can be a huge pain if you want to remove it) Now here's what I'm still a little hazy on: 1. What's the difference in cost of building a piston gun versus a direct impingement gun? And specifically what parts are different? 2. Is a midlength gas system, with a 16" barrel and 9" handguards the only setup which allows for the attachment of the M9 bayonet? Even if I never use it, it'd be a cool feature to have. And do you have to have a standard A2 front sight base to use it? 3. I've heard about fully shrouded firing pins. What does this feature do, does it cost more, and is it worth it? 4. What are material are collapsible/adjustable M4 stocks available in, and which would you recommend? 5. Should you definitely buy your barrel and bolt-carrier group from the same place and at the same time? I've read this ensures accurate headspace. And how do you know if this is correct otherwise? 6. I'd like to get a chrome-lined barrel for better functioning and longevity, so is there anything else that can be chrome-lined for better quality, and any that you would recommend? 7. Will a barrel with a 1:7 twist rate reliably fire all bullet weights, since it's capable of stabilizing heavy bullets? 8. Somebody told me that since I'm a noob to this, I should buy a lower parts kit and a stock kit to finish up my lower, and just buy a complete upper and pin it on. I'd rather build my rifle one part at a time (or one group at a time), as I browse the internet and find deals, which would also allow more customization and familiarization with my weapon. What do you think? Thanks in advance!