Musings on Compact AR's (CQB/Home D/Truck/BoB/etc.)
First, please let me note that I'm tossing this in "General" rather than "Pistol" or "NFA" because it touches on both. Also, I'm not trying to present myself as an expert, but as a student I'm trying to distill some things I've picked up from this community into a single piece I'm writing about "General Principles of Compact-AR Building for Non-'Gun People,'" so this is more asking the experts to look over my shoulder and give feedback on what I'm doing right and what wrong. WARNING: WALL O' TEXT AHEAD!
The first question we need to ask is Expected Maximum Engagement Range. If we're looking at a range outside of about 300 yards necessitating magnified optics, fixed front sights become a liability, but for unmagnified use their simplicity as "one less moving part to fight with" becomes an advantage. Whether that fixed sight is a rail-mount on a free-float or a Front Sight Base gas-block is up to user preference, though rail-mount does allow you to place the sight closer to the muzzle using more of the total length for sight-radius.
Second becomes whether or not length is important to you. Under Federal law, 26" OAL is the boundary between "Pistol" and "Title I Other Firearm." State laws differ about what constitutes a "pistol" eligible for CCW or Vehicle Carry, though. If you're under a 26" OAL Cap like Michigan has, Upper and Lower Receivers account for 7-5/8," which reduces your available length to 18-3/8", so you'll want to stick to a Carbine-length buffer tube, ideally as short as possible. The Brownells 7-1/4" at https://www.brownells.com/handgun-pa...34-192451.aspx is a good fit here, leaving 11.25" for the barrel and muzzle device measured from upper receiver front-face. The LAW Tactical sidefolder, which I consider a must-have for any tight-spaces AR, takes another 1.3" bite out of that, capping combined Barrel/MD at 9.95".
If you're unfettered by an OAL Cap, your next concern becomes overall layout--if you like to use the space in front of the folded buffer to carry a spare mag as I do, your buffer/brace length becomes limited by the position of your spare mag and its carrier. As a general rule, though, the Vltor A5 system is *the* way to go unless you physically or legally can't spare the 3/4" of added length, in which case you should use either a Geissele Super 42 or a PWS H2 buffer and Sprinco Blue spring.
Distilling this down to a set of general principles:
1. Less moving parts to fight with is good when deployment speed is of the essence. Stick with a fixed front sight unless you plan to use magnified optics, which are generally more Reach Out & Touch Someone than Close Quarters.
2. Shorter barrels require different buffer systems than normal to operate reliably; depending on length requirements the Vltor A5, Geissele Super 42, or PWS H2+Sprinco Blue buffer systems are your best choices.
3. Barring personal aversion to the contrary, at least one onboard spare magazine mounted right on the gun will give you a guaranteed-ready reload if you don't have time to grab your spares.
4. If building a 10.3"/10.5," start with a barrel made to NSWC-Crane Mk 18 specs. If building a 12.5", start with the specs for the GL/SSC--it's better to start with proven military engineering and adapt it to your needs with new handguards, sights and such than try to reinvent the wheel from scratch. If this is your first build, definitely have a trusted friend who's in the AR community help you with input on selecting parts, or join the forum at M4Carbine.net and ask the SME's there for advice.
5. If there's ANY chance of a low- or no-light engagement, you will want a weapon-mounted light. A tailcap-switched light mounted near the tip of your support-hand thumb will go a long way in both giving you illumination and blinding the threat, without the complications of installing a tape-switch.
6. For speed of acquisition, a compact, lightweight laser is a helpful accessory--usually rail-mount lasers designed for pistols such as the LaserMax Uni-Max fit this pattern, so they're a much better fit than the big, boxy military-grade units.
I'm sure there's more to the puzzle than what I have here, so any jog of my memory, suggestions or refinements on what I have so far would be appreciated--bear in mind, I'm trying to write this for people who generally aren't Gun People, like your typical Word/Excel "computer user" versus a more in-depth "technical user," and the goal is kind of a "Compact AR's For Dummies" general framework while leaving latitude to adjust for individual needs and preferences. Goal is to publish next Wednesday, but I can kick the can down the road as needed until it's ready.
