AR basics

I'm far from an expert, but Bob has a post up asking for AR advice. I threw in my nickel as follows; if you have any insight please feel free to put it in comments here or there or both.

Barrel:
1/7 and 1/9 are the most commonly found, although you’ll find some 1/8 and even as high as 1/12 in some applications. Roughly speaking, faster twist means heavier bullets stabilize better. That said, the 1/8 on my A2 shoots 45gr nicely. Every barrel has an ideal, but my rule of thumb is 1/9 for 50-62gr, 1/8 for 55-72gr, and 1/7 for 62+. If you’re planning to use 55-62gr surplus ammo, a 1/9 is just fine.
16″ is a good utility barrel length; handy enough to move with and long enough to keep blast down some. Chrome lining will be a good thing for your described purpose; it can degrade accuracy some but not enough to matter at home distances. We’re talking changing a 1.5MOA barrel to a 3MOA barrel.

Gas:
The AR was designed as a DI rifle. Don’t bother fighting that. Gas length… on a 16″ barrel, a carbine gas system is standard. If you’re using a front-sight gas block, it’s a pretty short radius. Putting a rifle-length system on a carbine barrel ends up with what’s called a “dissipator”, which I think looks freaking stupid but does give you a rifle sight radius. If you’re going with optics, go carbine.

BCG:
Matter of preference. I’ve got standard parkerized BCGs in all three of my current ARs, but I’m putting a Nickel-Boron plated group in my 300BLK build. If you intend to use it for hard use, it might be worth getting a MPI bolt group.

Upper:
Yes, what upper you get defines the gas length. For optics, I’d put on a decent set of irons to start and save a few bucks for an AimpointPRO or Eotech 512; they both run $400ish new. The forward assist is part of the upper, not the lower, and most rifles in your budget will have one.

Lower:
Get a mil-spec lower. Pick a rollmark you like and get that one. Avoid cast lowers. Spikes, Palmetto State, York Arms, (the list goes on) are good lowers. I’ve got one from Anvil Arms (since out of business), two from Territorial Arms (out of business), one from York Arms and another York on the way. They’re all solid. A generic lower parts kit includes a single-stage trigger that may or may not be decent. It’ll take you an hour and a few basic tools to assemble a lower. Worth doing just to understand how the rifle works. An upgraded trigger like a Timney or Geissele is a nice-to-have investment but not necessary. (And on a defensive rifle, I’m not sure a 3# match trigger is necessarily a good thing.)

In your budget, here’s my recommendation:
- pick a lower; any lower. Get a lower parts kit. Assemble. ($125 lower, $60 LPK)
- get a stock you like; a collapsible M4-style stock with buffer etc is a good bet. ($60)
- get an assembled upper from someplace like Stag Arms. I have this one on two rifles and love it. Spend the $75 for the “plus pack” for the 1/7 and MPI bolt if you want, but it’s fine without. ($465/540)
- buy an optic you like; start with a budget red dot (TruGlo is a good bet) if you can’t swing an Eotech yet. ($50-400)
- buy a pile of PMags ($15/ea)

Total: $760+ without magazines.