5.56 is better in the "overpenetration" department of concerns. Pistol caliber carbines suck ballistically and in many designs, the reliability and durability is questionable. I'd much rather my local Sheriff's department brought some quality ARs in 5.56 than some cheesy Sub2000 or an expensive and harder to support MP-5...the AR is a solid all round rifle chambered in a good caliber, especially for police use. Easy to support, affordable, parts widely available, etc, easy to shoot for a wide variety of shooters. It's not about "being cool" it's about choosing the most effective tool for the job. A 16" barrel AR is very usable indoors and out and you've got effectiveness out to several hundred yards if need be (although it will almost never be). No need for .308 with it's added expense.
FTR, I like the AR15 platform. Not love, but like. A like founded on intimate familiarity with lots of examples. After the Current Insanity, I plan on buying two more lowers and building custom serno'ed AR15s for each family member with an opposeable thumb. Suckers are easy to shoot. My primary problem is muzzle blast without earpro in close confines and the cost in $$$/PITA it would take to attenuate that. Not just
my ears I'd be &^%$ing up, either. LEO hearing is not magical and subject to the same physics as mine.
Overpenetration
A definite maybe. Shorty/shorter Ar15s are not going to generate lotsa velocity to get FMJ to bust up on its own too far past bad breath range. And short(er) ARs are all the fashion. Hopefully they are springing for some decent quality HP (or HP-ish) rounds for 5.56. Thing is, quality HPs also attenuate overpenetration effects of pistol rounds. A possible AR advantage, but not an overwhelming one, and not one that is indisputable.
Ballistic Suckage
Terminal, I presume, since urban lines of sight and LEO ROEs/force use policies are not likely to let non-sniper LEOS to take shots beyond where pistol vs intermediate trajectory is going to matter a hoot. Yep, 5.56 is generally more lethal, one for one. My experience with HK MP-5s is that shooting them is sorta like Lay's Tater Chips, can't hardly shoot just one round...especially when you can put an entire burst into a head-sized target at 50m, no sweat. Easier than with any AR 5.56mm carbine. But, yeah, 5.56 at 2700fps is n another league.
Quality
No doubt, the better AR15 assemblers beat KelTec all to hell WRT quality. They don't beat Ruger (discontinued pistol cal carbines), Beretta, HK, & such, some of whom actually designed the guns the assemble and may have
actually manufactured the parts (as odd as that may seem). Thing is, for an AR15 to stay reliable, it needs regular TLC. Probably more than the old Rugers, probably more than the Beretta carbines, and
definitely more than the HKs (I have side-by-side personal experience on that one: M16A2, CAR-15, M4A1, HK MP-5). Sadly, every LEO turn in revolver, pistol, and shotgun I have bought or handled has been filthy and ill-maintained.
I'd not trust the average LEO to keep an AR15 in running order. Recall the photo of NYC's Finest toting an AR15 with the optic on backwards? When Glock crafts a "safe-action" 5.56mm carbine as reliable as the usual Glock Shooting Appliance, then the intermediate caliber carbine will be reliable in LEO Lackadaisy's hands.
Besides, sucker is going to be shot infrequently during its short, ill-maintained service life and won't have to stand up to high round counts in non-SWATtie hands before they off load them to Summit, J&G, or whomever else.
Ergo & Service
AR15 is notoriously ergonomical, yup. HK is pretty good, and my wife liked the Beretta CX4. I'd have to spend more time with it to be sure. New & different. Not a big HK or Beretta fanboi (only bought one Beretta with my own $$$, no HKs), but they might not need service as much as your average AR. I'd like to see some third-party MTBF data, but I'd bet Beretta came out on top by a
wide margin, followed by HK, then any of the better AR15 assemblers (limited by design). I presume any of the big boys would provide adequate service to a LEO agency.
7.62
A rural LEO would likely be better served with a larger cartridge, given the 4-legged critter factor. 5.56 is legal for deer in Texas. Doesn't make it smart.
To sum up, AR15 has a lot going for it, but it has disadvantages that may make it less optimal than other LEO long gun options. Especially if the LEOs like their hearing and lack of tinnitus. An HK MP-5 or UMP in 9mm with a suppressor and 147gr premium JHP would be very easy on the ears and very effective in most urban situations. Same with the UMP in .45ACP. Heck, an AR15 in 9mm (147gr pills) or .45ACP would bring a lot to the table, too.
NFA of 1934 was a lovely little slice of idiocy for making it harder to counter muzzle blast and hearing loss. We hates it.
Using an AR, or other 5.56 capable weapon is not as far fetched as some people think. I currently use an AR180B with a ban era muzzle break on it for my HD gun. I haven't shot it indoors, but now that this thread has come about, I think I will, just so I know what to expect. I have a friend that will let me use his tack room, after all, he has already perforated the walls with #4 buck eradicating a raccoon or 4.
bob
Do it first with earpro doubled up. and get progressively more jiggy. If'n you stop before getting audibly naked, might want to think about why.
Fair warning: you are risking life long tinnitus. My tinnitus ain;t that bad, I hardly notice it most times nowadays. Others are not so fortunate.