I think my wife is getting me a stripped lower for Christmas (and even if she doesn't, I plan on getting one afterwards) and I want to build a pistol. I also know these questions have been asked before, but most of the questions are about ballistic effectiveness.

Last Sat, at qualifications for my PD, a guy brought am AR pistol with an 8" or so barrel. This is the first time I have ever gotten to play with one, or any short barrelled AR for that matter. Seems VERY handy compared to my 16" carbine, considering my primary use for an AR will likely be in and around vehicles and buildings. He had some kind of muzzle brake on it (he couldn't remember which brand or model it was) and, when fired, it was like a flash bang going off every time. HUGE muzzle flash, LOUD and obnoxious muzzle blast, even when wearing muffs. It was so bad on an outdoor range that I can't even imagine what it would be like if shot inside a building. I know the brake contributed to this, but how much? I realize that the short barrel combined with a high pressure rifle cartridge doesn't help, either. I realize that, even with a 16" barrel, an AR isn't anywhere near hearing safe, and that if I ever have to use it, hearing damage would not be real high up on my list of problems, but I don't want to blow out my ear drums or stun myself stupid on the first shot, if possible. I also know that the short barrel will have more muzzle flash as a result of the short barrel with the rifle cartridge.

When I took my rifle instructor's class last month, one of the instructors had an SBR issued from his Department. It was either 11 1/2" or 12 1/2" barrel, based on how much barrel was exposed past the front sight base, and had an A2 flash hider. I was going to ask him which it was but didn't get a chance to. It didn't seem much, of any, louder than the rest of us with 16" barrels, on the outdoor range, anyway. He didn't shoot it at the night shoot, so I wasn't able to gauge how bad the muzzle flash was.

My plan is either an 11 1/2" or 12 1/2" barrel in 5.56 with a flash hider, not a brake, and an SBA3 brace. Barrel will likely have a carbine gas system, if it matters, with a fixed front sight tower. I'd like a pencil or light profile barrel because the gun is a LOT more likely to be carried a lot than shot and the weight savings would be wonderful for a beat up, broken down old man. For those with experience with them, how bad is the blast/flash with a flash hider? Is the extra 1" of barrel length between the two worth it? I'm not as worried about ballistic effectiveness since we are using Speer 55gr Gold Dots as a duty load at the PD, but I am curious about this as well. Since this will be my only AR for the time being, besides a 20" HBAR (my carbine started out as a pre-ban Colt Sporter Match HBAR and I'd like to restore it to this configuration), it will be my "do all" gun. If the mythical "SHTF" ever happens, can I expect the shorter barrel to work at a reasonable distance (meaning what is the approximate range the ammo will reliably fragment) with M193 spec ammo? Also, if anyone knows, what would be the approximate distance that I could expect the Gold Dots to reliably expand? That's not a real big concern for me, I have other rifles I can use for longer range if it ever comes to that, but I'm curious.

Muzzle device is likely to be an A2 flash hider, unless there are suggestions for a better flash hider that doesn't cost an arm and a leg. It's probably never going to be suppressed unless suppressors are removed from the NFA, so compatibility with a suppressor isn't necessary, just a decent quality, reasonably effective flash hider.

Also, one other question. I have read a lot about it, but there doesn't seem to be any real good answers. Since cost is always a concern for me (I make a street cop's wages, decent but not great), is there a real big difference in performance and longevity between Melonited/nitrided barrels and traditional chrome lined? I have read and seen videos that nitrided seems just fine and just as durable for semi-auto use and I really like the corrosion resistant properties of the nitrided barrels, especially for a gun that will likely spend a lot of it's life kicking around inside a marked police cruiser. On the other hand, I have also read that chrome lined is superior to nitrided, so who is right? Reasonably long life is more important to me than the corrosion resistance, however, so if the chrome lined is that much better, chrome lined it is. The vast majority of the ammo fired will be reasonably rapid semi auto, possibly long strings in training, heating the barrel up quite a bit, although not as much as full auto. Since we are able to actually carry ARs now any my PD, I plan on shooting and training as much as I can, although probably not as much as a lot here do due to cost of ammo.

I'm not so much worried about the rest of the parts. I already know to buy as much quality as I can afford to and stay away from bargain basement parts.

Thanks for any and all assistance. I really appreciate it.

Bub75

I like nitrided barrels, and both my 10.5" barrels with 3 prong flash hiders don't seem excessive shooting indoors.  The same barrels with brakes were ridiculous.  Crowd pleasers, but disorienting to shoot, especially fast.

10.5 is a pretty popular minimum length for 5.56.  Honestly, even out of a 7.5" barrel, you can get reasonably small groups at 100yd and the rounds will penetrate several boards.  I wouldn't use it for hunting, but I also wouldn't want anybody shooting at me with one.  The loudness is also a factor.  If you do order a 5.56 barrel in the 7-8 inch range for self defense, ho ahead and pick up a book on sign language.  Cause if you ever have to fire it without hearing protection, you're looking at permanent hearing loss to some degree.  10.5" 5.56 is loud.  8.5" will shake your teeth.

For finish, nitride is perfectly fine for most shooters.  If you want to use it as a full auto bullet hose, CHF+chrome lined will help it not wear out.  The amount of ammo it takes to shoot out a nitride barrel is many times the cost of a new barrel.  If you can afford to shoot one till it wears out, you can afford to replace it without any trouble.

I have a 10.5" Novekse 5.56 upper that had a Battle Comp 2.0 MB like this one https://battlecomp.com/product/battlecomp-2-1-black-melonite/ and it was crazy loud and concussive.  
If I went to a range Shooters on either side of me would look annoyed and move away.

After I got my cans I replaced them with Surefire Muzzle Brakes, problem solved.

.oops never mind.....lol

5.56 still functions well in penetration and accuracy out of a 10.5" barrel but I would not go smaller than that.  If you do want to drop down to a 8.5 or 7.5" go with 300 BO.  You can fire it subsonic and still get good performance but reduce the gas blowback and recoil.

Also a nitrite barrel should be fine.

As far as an ~11.5'' AR and fragmenting, I think it's somewhere around 100 yards or a bit less. Just because a bullet doesn't fragment doesn't mean it would be ineffective and most shooting takes place at reasonably close ranges anyway.  
An A2 flash hider actually works pretty well. There are better flash hiders but they generally cost far more and are not significantly better. The most effective flash hider I have seen is a Smith Vortex, it is amazing at eliminating flash IMO. A Vortex costs around $50. Unless you really care about as little flash as possible an A2 is a good choice and a better hider than most.
Nitride is superior to a chrome lined bore/parked exterior barrel as far as the finish. Assuming both barrels are equally made and the only difference is nitride vs. chrome lined the nitride will be more accurate, more corrosion resistant, more scratch/ scuff resistant and longer lasting. Chrome lined barrels are also a good choice but a bit redundant with the rise of nitride.  Either will last a lifetime and take a fortune in ammo to wear out anyway.

Thanks, guys. I appreciate the help. Now to go shop and try to figure out what I want. Probably an 11 1/2" barrel, we'll see.

Bub75

Nitride is nice to have. Adds to the expense, and any velocity difference could be made up with a hotter round. My 6.8 is nitride, the 5.56 pistol was just cheap phosphate no chrome. Really not an issue.

"Flash hiders" and "muzzle brakes" are, in that order, loud and louder. What you want is a linear compensator, ie a screw on device with no gas outlets on the outside, they are on the end where the bullet comes out. They direct all the gas forward and it really reduces the noise at the ear when shooting.

Fired four shots with my AR pistol first day of season at the Ozarkius bulletproofus we hunt and barely rang my ears. Really. However, that same pistol under a canopy will blow right past a set of plugs and muffs. Again, how the muzzle blast exits and if it gets redirected is what you hear, ie nobody says shooting inside a building will go easy, regardless of what it is.

As for recoil its 5.56 or similar, what recoil? It's not timed splits in competition. This is where a race comp on a street gun comes into play, it doesn't work any better than target sights on a CCW. Good luck with hearing, good luck with a smooth draw. Don't use race gun parts on a field hunting gun. Or, go deaf. Your choice.

One thought is that if you are using it at an intruder why not have all that gas go right into his face? What point is there turning it sideways to mess with you?

BTW the 10.5" barrel has been around since 1965 - the XM177. Colt dun figgered it out a long time ago. Another inch might help, but some claim it's not how long the barrel, it's how you know to use it.

I have a 7 inch barrel with an A2 hider. its loud as hell and throws a pretty big fireball... dont get that...

stick with 10.5 or so.

The XM177 was made in ~9.8' and ~11.5'' labeled E1 and E2. The ~10.3'' came much later as a result of cutting down M4 barrels.

Good point, this is where the Noveske Fire Pig come in...  Directs concussion and blasts forward...

My 10.5" doesnt seem any louder than my 16" when shooting outdoors. Not sure about muzzle flash, never paid attention or shotbat night.

A couple people hinted at 10.5". From my understanding, that length is so popular in 5.56 because any shorter you need to use the less reliable pistol length gas system. IMO, if you want short for manueverability, nonreason to go longer than 10.5. Google "balistics by the inch" to see a chart with velocities from different barrel legths. Then compare that to what velocity a particulr round is effective and you can find the effective range.

If you want to go short and you're concerned about blast to the shooter, just use a linear comp or a muzzle that will allow you to use a blast shield. I have two uppers way shorter than what you're looking at and have no issues with concussion, even indoors.

5" Sports a SLR Linear Comp.
8.5" uses a Strike industries King Comp and Oppressor blast device.

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If you want super short 7.5"-8.5" go with 300 blk, same bolt and magazines as 5.56mm. All ARs are going to cause hearing damage, and given your situation having to use them for patrol I would highly recommend looking into a suppressor. They are not the difficult to get, I know it seems like a lot of work but it's really easy. Get your finger prints done, two passport photos, fill out the form 4, dealer will help with this, send you $200 and your done, wait 6-10 months. I will never go back to shooting ARs without a suppressor.

I would recommend at least an 11.5" and a linear comp to hopefully blow the sound forward. A2s are very obnoxious especially in confined areas, let alone outside.

Your not going to save a ton of wieght when comparing a LW profile to Govt profile, a few ounces at most.

I just bought a complete Ar15 7.5" nitride pistol kit for $239 shipped from PSA. I have not had a chance to shoot it yet. It looks and feels like a top notch  product.
Also added a Sig Sauer Romeo5 red dot ($129 at PSA).

Echo the above. I just copped a few 10.5" 5.56 PSA uppers in different flavors (pistol and carbine gas) and that is definitely the barrel length I would go with in your situation OP.

I have 10.5, 11.5, and 12.5. The 12.5 is my favorite, but I like 11.5, and they tend to be easier to find. The 10.5 is viable, I just like a bit more velocity and dwell time.

Most of my barrels are nitrided. If I shot FA or did mag dumps, I'd go chrome. But, even if the barrel only lasts 10,000 rounds (I think a conservative estimate), you're still looking at a tiny cost compared to the ammo cost. A single case of 5.56 costs at least twice what you can find a decent barrel for.

Nitride and chrome lining are essentially the same in terms of hardness. One is a coating, one is a surface treatment. Either may be slightly harder or softer than the other depending on the base steel and the nitride process. Nitride being as hard as chrome but much thicker, like 20 times thicker, will make it last longer than chrome under semi auto use, (even mag dumps). Chrome lining on a semi auto AR has nothing but disadvantages compared to a properly nitrided barrel.
You mention full auto or mag dumps as a reason to choose chrome.  This has partial justification. Since nitride relies on hardening the base steel, it also relies on the base steel when it comes to the melting point. Chrome remains harder than nitride at a certain temperature because it has a higher melting/ annealing point. The temperature it would take to make nitride begin to wear faster than chrome is far beyond what any semi auto fire could produce, it's somewhere around 1000 rounds in full auto on 4150 steel. If someone was literally going to fire that many rounds in full auto, chrome lining would begin to have a wear advantage after that point. Full auto ARs are not designed or generally capable of shooting that many rounds in a row so even full auto ARs do not benefit from chrome vs. nitride.
Most barrels are ruined from throat erosion and neither chrome or nitride are able to withstand erosion after a certain point. Nitride being much thicker gives it an advantage to throat erosion even at extreme temperatures. After 1500 rounds of full auto a chrome lined barrel will likely be ruined from throat erosion because the chrome was ripped away and the base steel was eroded. A nitride barrel 'may' have more bore wear after 1500 full auto rounds but the nitrided throat may still be intact and leave a usable barrel. So, even after 1500 rounds of sustained full auto ................

This is my take after much research on the subject. Now, does any of this matter when you consider either barrel may last 30,000 rounds and never see sustained full auto? Even a 4150 non lined barrel will last more rounds than most people will ever shoot in a couple lifetimes.

I'd like to see thermal imaging comparisons, but I believe that chrome reflects heat much more effectively (similar to one of those thin mylar emergency blankets trapping heat).

Also, I think the quoted surface hardness of nitrided barrels tends to be exaggerated- while you can nitride steel to insane hardnesses, I think barrel companies shy away from it (dunno if you lose toughness by going that hard). Whenever I've seen hardness tests done, the steel tdnds to be very hard, but not near the quoted values.

I have a 7.5" 5.56 AR pistol with Kaw Valley Precision linear compensator and outdoors,
I don't find it to be any louder than 16" rifles next to it.

OP, are you limited to 5.56?
I also have a 5.5" 9mm AR pistol with dedicated glock magazine lower,
Spartan lower and upper from Joebob's (NFA) with an SBA3 brace very compact and fast handling.
Uses any 9mm Glock magazine, with you being LEO, you may already have magazine interchangeability.
Here is a photo of the two together:
(Plan on replacing the CAA buffer tube cover with SBA3 brace as soon as finances allow.)
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To the poster that asked, yes, I am restricted to .223/5.56. Looks like it’s gonna be 11 1/2”. Now, to find someone who has an 11 1/2” with fixed front sight base in stock. Thanks for the help all. I appreciate it.

Bub75

Colt 11.5" HRT/FBI HBAR $250 w/ FSB

I'd say go 7.5-8" with a linear comp or a 10.5-11.5" with the A2.

Here are a couple:
https://palmettostatearmory.com/psa-10-5-carbine-length-5-56-nato-1-7-nitride-classic-shockwave-pistol-kit-olive-drab-green-5165449225.html

https://palmettostatearmory.com/psa-10-5-5-56-nato-1-7-nitride-moe-ept-shockwave-pistol-kit-black-5165449862.html

If budget allows includes SBA3; fde, black oos currently
https://palmettostatearmory.com/psa-10-5-carbine-length-5-56-nato-1-7-phosphate-9-lightweight-m-lok-moe-ept-sba3-pistol-kit-flat-dark-earth-5165449772.html

The low priced, yet lightweight and high quality KAK flash cans work very well on short AR pistols in reducing blast and noise to the shooter.  It redirects it downrange.  Stainless barrels work very well also and clean up as easy as a chrome lined barrel.  This is a 7.5" with he KAK flash can and while I don't shoot without ear protection, it isn't as loud as my 10.5" pistol with the A2 flash hider/brake.  The pistol below is set up for home defense and works very well and highly accurate.




I built this one with a PSA upper with a chrome lined hammer forged FN barrel and also works great and is a simpler more utilitarian set up.  I built it to be as close to the Commando style carbines used by the military.  It is a bit louder than my shorter barrelled pistol.  Both pistols have the SBA3 brace which is the best pistol brace out there at the moment.

Since this is going to be an all purpose gun, I think I've pretty much decided on the 11 1/2" barrel. 11 1/2" seems to be the best compromise between having a handy length while still maintaining decent velocity. If I can swing it, barrel will be a Ballistic Advantage with a QPQ finish, if it is in stock when I'm ready to buy. There are a few places to buy them with an "F" front sight base, barrel nut, delta ring and all the rest already installed for not much more than the PSA barrels and, from what I have read, they are universally very highly rated. For a little more, I can also get it directly from Ballistic Advantage, if the others are out of stock. I'll check out the KAK flash can. I already plan on an SBA3 brace, it seems to be the best option and is adjustable. Due to Christmas coming up, it will probably be late Feb or March till I can buy some of the high dollar parts and get the build done. When I do, I'll post pics. Again, thanks for all the help.

Bub75

bub75, sounds fun like a fun build. I'm squirelling away some things (including $$) for something similar although with a BA 11.3" .625 bbl & going lo-pro rather than traditional FSB.
I've been a really good boy (mostly) so maybe Santa will help out with some of the little odds & ends.
Good luck.

11.5" is an ideal barrel length for 5.56 for most purposes.

I don't know why that 1" difference between a 10.5" and 11.5" is so consequential on concussion, but it is.

I don't really hear or notice that much difference between a 14.5" or 16" and 11.5", so I've always been a big fan of 11.5" barrels in 5.56 NATO.

Plenty of velocity, compact, not too loud like the shorter pipes, and they can be suppressed without creating an overall length that is a huge penalty to maneuverability.

And that's another consideration, although not a big one. I don't own any, but at some point, I'd like to get a suppressor. With an 11 1/2" barrel, once a suppressor is installed (depending on the suppressor, of course), it should work out to be about the same length as a 16" barrelled carbine. As well, once all the out of state family passes away (and I no longer need to worry about paperwork to legally take it out of state), and I retire and there's not anywhere near the possibility of having to use it and having it sit in evidence for a LONG time, I may send in the paperwork to SBR it. That so far in the future, though, that I'm not even worried about it right now.

Bub75

Well, the first part was purchased. Last night, I saw a post in the optics and red dot sub forum about affordable red dots. PA_Mike posted that Primary Arms had FDE variants of their advanced red dots on sale for $99.00. They usually run $169.99 or more. They got great reviews and it would take me a LONG time to save for an Aimpoint or similar, so I fo’ed. I’d rather have a black one but black wasn’t on sale. Should be here next week. It’ll go on my current 16” carbine for now but will go on the pistol when done. Feels good to buy stuff!

Bub75

Bumping this thread to continue the discussion of super-short ARs.

@LRRPF52, I'm planning to build a 9" SBR PDW carbine. Why 9" you ask? Because I want the NT4 MAMS comp as close to the end of the 8" URX 3.1 as I can get it while still being able to get my NT4 suppressor on and off.

My concerns: cycling reliability and the muzzle blast beating the guts of my corncob out. I have zero concerns about muzzle velocity as this will be an exclusive close-quarters blaster.

Thoughts?

I have a Dragon's Head on my 7.5 and it really helps send the noise and flash downrange.  I can even shoot it indoor without my teeth rattling.

https://www.surplusammo.com/products/saa-5-56mm-dragons-head-muzzle-brake-linear-compensator-gen-i.html

There are some videos of ballistics testing done by Arfcom where some loads were proven to work very well from 7" ARs IIRC.

AR15.com ballistics testing

This is my first pistol build I did last fall. I was on the fence for awhile too, deciding between, 10.5” & 11.5”. I went the Faxon 10.5 on a Aero Precision Upper and Lower. I run a Black River Tactical Covert Comp on it an like it a lot.

I’m in the middle of building my 2nd AR Pistol using Aero Precision Upper and Lower with a Ballistic Advantage 11.5” barrel. I plan to put Shorty Smith Vortex on it and run a 1-4 Scope.

I’m already thinking about my 3rd pistol, which will be a 11.5” with fixed front sight and carry handle rear. Probably will use either Spikes or Aero Upper and Lower on it.

Aero Precision Pistol by A B, on Flickr

Thanks. With the use of the M4QD MAMS, you reckon it'll be too abusive on the NT4 can? Those things are built like tanks but it's still a concern of mine.

I have 4.75", 7.5", and 3 10.5". But there is a huge difference in maneuverability in the 3. And they will all put holes in what your shooting at.

Go on the lighter side when you build. Faxon 10.5" pencil barrel, Midwestindustries 10.5" 6oz rail, and a Brownell's low mass BCG. That just did you a big weight loss and at affordable prices.

Lighter the better. Add the SLR adjustable gas block.

Add a lightweight optic and you now have a laser beam.