I'm looking to build a dedicated SBR for duty use.

What's a good length for a patrol carbine in the urban environment?

This will be a host to a light weight can and ride in a cruiser.

DI or Piston?

I use an LMT 10.5 upper on an SBR lower. I mainly chose it because I was in Narcotics and used it while doing search warrants. Since I have gone back to Patrol I have through about using a title 1 ar like my 14.5 perm but I jst kept using the 10.5. I have two other sbr ar so I figure I might as well keep this on in my patrol unit. I think for me the 10.5 is fine for the ranges I would use it. Ymmv. Make sure it is cool with your dept. to use an sbr... Some are funny about that.

Eta  mine is direct gas, I never got into the pistons. I dont use a can with mine on duty, but I do have a few... I would deff go 10.5 or maybe 11.5 if it is gonna have a can on it to keep the length down. I might form one or buy a micro can for mine one day...

James

DI.

Does the rifle ride next to you or in the trunk?

If it rides next to you, do you have a way to secure the suppressor in case someone decides to smash the window on your cruiser? The rack locks, but what prevents the suppressor from being stolen?

If it's suppressed, a 12.5" with a short, lightweight suppressor like a Gemtech Trek T or a Griffin Armament Spartan 3 would be nice. If it's not suppressed, I'd probably do a 12.5" or even a 14.5" barrel.

11.5-12.5.

For a duty rifle...
Unsuppressed 11.5-12.5
Suppressed 10.5-12.5

The rack unlocks with the flip of a switch. What's to stop someone from doing s smash and grab of the shotguns and/or an AR?

It'll either ride in the rack or cargo area (Explorers).

I'm looking for a short/lighter combo of gun and suppressor.

No policies towards SBRs or cans other than we have to qual with them.

What is your issued ammo? For patrol, do you ever see yourself realistically needing to take a shot farther than 100-200 yards?

Depending on the performance of your ammo, I'd suggest a 10.5" barrel with a "k" style can like the Saker556k or the Specwar556k.

Keep it as short as possible in case you need to use it while seated and out of the window of your truck. YMMV.

In our Crown Vics, the rack would only open with the key in the ignition. If yours unlock with the flip of a switch without any safeguards, that's not a great setup. And since it's an Explorer, there's no real protection in the cargo area either.

So since the whole rifle will be unprotected, I guess you don't have to worry about protecting the can itself. It'll be stolen along with everything else if someone decides to.

A 12.5" with a Spartan 3 would be my choice. It should fit anywhere a 10.5" would with better fragmentation performance.

Since you specifically mentioned using it in your cruiser, I assume rapid deployment is an issue. I have a 10.5" build which is great for range use and competition, but I think it would be difficult to deploy from a seated position in a vehicle. Have you considered a Sig 556 variant with a folding stock? Alternatively, you could do an AR build with a folding stock and add a Faxon upper so that the weapon could be filed while folded if the situation ever necessitated it. Just my 2 cents.

11.5-12.5

This

Yep I agree.

and run some heavy loads like the 77GR SMK OTM stuff.

11.5







11.5" allows the most versatile range of usage with extreme reliability across the board. I have a fullsize can (M4-2000) on mine. Motorpool just fabricated this rack for me on my 29th birthday. We've got a really talented trustee there, Robert, who takes good care of my unit. I don't normally like a single-point sling, but so far it's been the best option for rapid-deployment without getting snagged on anything. I have a kick switch to unlock this one. (I leave my key in the ignition always, and a belt key unlocks the door.) The can cannot be unscrewed while in the lock, but if the can is off, someone could collapse the stock and remove the weapon. Whatever. I used to just lay it against the passenger seat, so this is way better. lol



Oh, and if I know I have to go into a really cramped building where space is tight, I ditch the can. Usually in those instances I have time to don my Peltor Comtac 2 though.

We issue Win 62gr SP.

Sexy!

What are the specs of the rifle?

I'm still thinking a shorter can would be best so it doesn't negate having a short rifle.

If your duty ammo has good terminal performance out to 200 yards from a 10.5" barrel, I'd still consider it a good option.

A few larger agencies just transitioned from a 14.5" to a 10.5" barrel after a comprehensive balistic test with the Federal XM223SP1 (Fusion) 62gr round.

Agreed on the can, keep it short and light as well.

No. Something bonded or monolithic that goes well through autobodies and glass.

Unfortunately we're issued American Eagle 55gr FMJ Boat Tail for duty use.

If that is what his main concerns are then sure.  MK262  is legit stuff from what I have read.  SBRs need a heavier round to be as useful as a full length rifle.

ETA: 55gr duty loads aren't going to cut it

I think 10.5-11.5 is perfect for duty use

Read up on the 50gr TSX.  Or just take some deer hunting.

I was talking about the OPs issued ammo.  That 50gr tsx looks good to go.  

We have to carry department issued ammo.

11.5" is about as good as it gets for ARs IMO.  There is a pretty significant velocity drop off once you drop below 11.5 so it is really as short as you can go without losing too much.  My 11.5" averaged 2907fps (about 15ft from muzzle).  I wish i would have chrono'd the LMT 10.5 I had out there but i didn't .  I felt pretty good about the 2900fps.

Bullet weight matters a lot less than it used to. The 50-70TSX are all good and the 55/62gr bonded bullets from Federal perform very well on auto bodies.

Mk262 is great ammo for long range or exposed targets. It's mediocre for targets in vehicles. This is a serious concern for police more so than military due to the nature of their shootings and the lack of belt fed or high explosive weapons.

Makes sense. I will check out the rounds mentioned.

It's a Colt Commando clone...
Daniel Defense 11.5" LW barrel (from back when they shipped .625" at the FSB)




LMT M16 BCG and gen2 M4 stock + receiver extension (buffer tube)




Colt H2 buffer




Wolff XP action spring




AAC M4-2000 on 51T Blackout FS




PWA Commando lower




EOTech 553.A65



GG&G MAD BUIS



Magpul ASAP sling adapter



generic single-point sling identical to this
Your thinking is sound, regarding keeping the can and barrel shorter. If I didn't already have this setup before becoming LE (or if I was building a dedicated suppressed setup), I would go with a shorter can and probably even a 10.3-10.5" barrel. That's just better for in/out of vehicles, and I'd never have to consider removing the can for a really confined structure.
Mine is setup this way because I want it to work with a wide variety of ammo (anything I grab) both unsuppressed and suppressed, without having to adjust anything about the setup.
When I want suppression, I want maximum suppression. (The flash suppression without the can is also great.)
For LE work, being able to hear/communicate during and after the gunfire is good enough. If you are issued one type of round, you can "set up" the weapon and dedicated can combo strictly for that round with no problems.
I have other hosts for the can, so mine doesn't always live on this one weapon.
Another factor favoring a shorter barrel is that it's less likely the slight increase in max effective range an extra inch buys you is worth the maneuverability handicap, when considering published stats on LE engagement distances. (I DO tend to always assume I may have to be THAT GUY that needs to take a 200(+) yard shot one day. You really never know).
Everything Combat_Jack said about ammo is correct. Our issued 62gr SP ammo isn't a horrible choice, but there are better options available. 55gr FMJ is truly a poor choice, especially with today's options AND American Eagle's weaksauce loading on that stuff, which is manufactured just for plinking/training/messing around.
There are plenty of reports and real-world performance data, testing, etc. which I bet you could get from LE firearms instructors for the asking, that would show why that is a poor choice for issue. I would attempt to steer administration away from that choice, if at all possible.
Dang it, now you've made me want to build a dedicated 10.5" + short can setup using the M16A1 which I was recently issued and a DD Mk18 rail a friend gave me.




Mk18 Block II time?

It would be the most legit "clone" ever. Yeah, gotta do it... lol