Quote:
Originally Posted by HorseSoldier
On the AR, pretty much all the magic happens in the upper receiver, so as long as the sights or optic were pre-zeroed, installation on a lower wouldn't make any real practical difference.
Beat me to it. Upper to lower fit doesn't matter much at all. Even the accu-wedges are more for the OCD portion of the shooting community than anyone trying to get better performance.
The modularity aspect for the individual Big Army troop isn't that great a strength on the AR/M16/M4 for the simple reason that it isn't used as such -- units just don't have additional specialized uppers, etc. However, I know a lot of SF guys, in some cases entire ODAs, that have deployed with multiple uppers for their M4s, and some guys who used SPR uppers on M4 lowers with pretty good success (trigger is not as good as the one on the issue SPR lower . . . but non-match grade M4 triggers never had an army-wide safety warning about match grade triggers failing on the SPRs).
It makes pretty good sense if you're either doing mounted operations and have extra stowage for spare uppers (starts making much less sense when you've hauling a golf bag of gun parts on your back on a ruckmarch) or if your mission set(s) is/are deliberate enough you can preconfigure your weapons -- going into Fallujah, maybe 12" barrel uppers are preferable, patrolling some wide open stretch of nothing in Iraq or Afghanistan, maybe 18" uppers are better.
That said, the bigger show stopper in my experience is ammunition quality rather than optimizing barrel length. With good ammo (Mk 262) and an ACOG, shooting unknown distance targets out to 600 meters gets boring, and (with the aid of a ballistic computer and spotter making wind call) I've seen a guy make a hit on a steel chest plate out around 1200 meters with a 12" upper. With standard issue green tip, you're probably more consistently in the 3-4 MOA (and realistically, anywhere from probably 1.5-6 MOA, depending on lot), which out at 600 which is pretty much just rolling the dice before you even start worrying about things like wind, bullets going transsonic, and such.
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OK, lets dispel one thing right now. The M4 is a pile of shit. It was designed to be a handy rifle for non-combat, support troops. Just like the M-1 carbine was designed for in WWII. A replacement for a pistol. The M-4 jams up after 2, 30 round mags, and over heats. Because it is not meant to be in an extended encounter. You can say well "professionals", and spec ops use it. Yeah, well when your choice for a short barrel rifle is and M4, or an M4. You obviously pick the M4. People seem to think that PMC's, and Spec ops can grab all sorts of neato crazy shit. They get whats in the armory. Whats there? Sig 550? AKSU74? Colt MARS? CZW-438? No, M4s, or an M-16A (whatever.)