7.5" Barrel AR-15s

[Tirod]

There is a practical purpose.

First, self defense. The shorter barrels offer plenty of ballistic power - rifle power - which is much higher than most pistols. Since the barrel is so much shorter it then offers more maneuverability in urban construction and exiting from vehicles. This is why the DOD moved from 20" to 14.5", and why smaller special units use the 10.5" Mk18. Shipboarding and urban townhouse assault, for example.

The Army has been using 10.5" barreled AR's since the 1960's - It's now a 50 year old concept and well proven.

So, sorry if some haven't got the memo.

As for 7.5", 5.56 isn't optimal. Go .300BO or 6.8SPC and the ballistics step up significantly, but the ammo costs don't go down for practice. That's why so many stick with 5.56.

In civilian life, what happens on a range might be one users toy, but hunters are another matter. In MO, the AR pistol is - a pistol. It can be used in rifle season as well as it's own Alternative season, for a total of 4 weeks. A 10.5" barreled pistol can be expected to have 1,000 foot pounds well beyond 125m - which is a common limit to hunting whitetails in broken Ozark woodlands. Using 77 gran OTM or TMK, there is plenty of ethical power and range, plus the advantage of light weight and a significant reduction in weapon length while trying to move quietlyn thru dense underbrush - where I've staked out a hotspot for deer laying up after leaf fall.

I could take the 6.8 again, but building another AR needed a purpose - another reason for the shorter barreled pistols.

And as a reminder, some of us build them because they are legal. Complaints about that are just disarmament fodder for antigunners. I don't need anyone's permission to do what is my right.

As for the muzzle blast, there are things like electronic muffs, silencers, and ear plugs. An AR pistol with linear brake is no worse than a 16" AR with side exiting muzzle brake - and in most cases, a lot better. One shooter took his to a carbine course over a weekend, shot over a thousand rounds on the line with RO's in close proximity, and when he asked "does the blast bother you?" he kept getting quizzical looks. They didn't get the point of the question. It wasn't as bad as the compensators and brakes we've seen marketed that run the guys in the next lane off.

As for accuracy and range, they have been known in the hands of decent shooters to hit targets out to 400m - with lethal results on humans.

All this, of course, is documented on the internet, which is where I found it over the last three years. If the first someone bumps up against it is loud noisy shortbarrels deliberately built to make noise on the range, I'm going to suggest you are only seeing those who built a range gun. Those with more serious intent know how to configure them properly and when and where they are used - not on a sunny Saturday afternoon showing off to their buddies and all.

 

[Olympus]

Again, I'm not interested in 300blk or 6.8. Also not interested in 10.5" ballistics. I'm interested in purely 5.56 from a 7.5" barrel. That's info that I haven't asking about from the beginning.

 

[MachIVshooter]

Sure I do, hydrostatic shock and all that

Hydrostatic shock is a misnomer (static = motionless). But yes, hydraulic shock that is sufficient to stretch tissue beyond a temporary cavity, creating a permanent cavity much larger than the projectile. This phenomenon begins to occur around 2,000 FPS, factors more and more as velocity increases.

It's not an end all be all, and just doesn't come into play here.
The .223 or 5.56 fmj's are not effective at speeds under the velocity needed to fragment, which is about 2700+ fps. Repeating that term doesn't change physics, millions of dollars worth of govt. number crunching and field studies, or make a death ray out of an otherwise underperforming round.

I never said it was a "death ray", but fragmentation is not required for a larger-than-projectile permanent cavity, and 2,300-2,400 FPS rounds do create such a cavity, albeit not as nasty as the same bullet 800-1,000 FPS faster.

Is there? If a .223 bullet fails to expand or fragment at 2400fps, is it going to be a significantly different wound pattern than an identical bullet that doesn't expand or fragment at 1700fps?

Yes. That's what I've been trying to explain.

I don't think you yourself understand what you are referring to.
The "2000fps threshold" isn't the point when animals get blown inside out from the sheer velocity of a projectile.

Never asserted such a claim. Stop making strawmen.

Its when a projectile designed to expand or fragment at rifle velocities starts behaving differently upon impact, by expansion or fragmentation. If the projectile fails to expand or fragment at 2400fps, the "2000fps threshold" won't make it more effective than one going 1700fps.

Using your logic, a .50 BMG FMJ round is no more effective than a .50AE FMJ round. Because velocity doesn't matter in the absence of expansion or fragmentation, right?

From the book
Wound ballistics; basics and application...chapter 4.3, page 213.
https://books.google.com/books?id=q4...eshold&f=false

"There is currently no evidence for the existence of a velocity or energy threshold for conventional designs of handgun or rifle bullets above which different wound ballistics phenomenon would occur.
However, there is a velocity threshold at which the behavior of a bullet changes. Full metal jacketed bullets remained shape stable on impacting water or gelatin at velocities up to 500 to 600m/s. At higher velocities they begin to deform or fragment."

Thousands of trauma surgeons and coroners disagree about the velocity aspect, as do other reputable experts, such as Dr. Martin Fackler.

Kinetic energy in and of itself means nothing, though. So no, there is no energy threshold.

And no, it's not like you get a handgun wound at 1,999 FPS and a rifle wound at 2,000; As I've said repeatedly, the phenomenon begins to occur around 2,000 FPS.

Ok, so you got an M193 to go 320fps UNDER the effective velocity of the round.

Again, I don't use ball ammo outside of practice and plinking. Why do you have it in your head that the performance of ball ammo is all that matters?

I go by what Ballistics by the Inch gives me in real world numbers.
http://www.ballisticsbytheinch.com/223rifle.html

Of which they used only one load; UMC, like PMC, is on the weak side. Lake City/Federal is who actually makes M193.

50 grain Vmax handloads?

Did I s-s-s-stutter? Yes, 50 gr. boat tail Hornady V-max bullets loaded into 5.56x45mm NATO cases with CCI400 primers and a variety of differnt powders. Clear enough?

http://www.hornady.com/store/22-Cal-.224-50-gr-V-MAX/

you'd better have boutique bullets to get any kind of expansion.
Sounds pretty boutique to me
Regardless, they are completely irrelevant to the discussion as they cannot be obtained by anyone other than you.
"50 grain vmax handloads (that only I have)" is pretty vague and unverifiable.
On a lighter note however,
A Vmax might just be the ticket though, at that lower speed it might retain enough weight to get through into vitals.
I know after seeing what it did to a coyote at closer to 3100fps, I wouldn't trust my life to it stopping a large, enraged bad guy. Basically made a really nasty flesh wound and left me with one wounded 40lb coyote.

One anecdotal coyote hit is the basis of your entire analysis of the V-max, then? Brilliant. By that measure, I can deem my .17 Rem with 20 gr. V-Max loads the end-all, be-all, since the last coyote I shot with it dropped with not even a twitch.

Also, they certainly are not a hand loader only proposition:

http://www.midwayusa.com/product/18...3-remington-50-grain-hornady-v-max-ammunition

http://www.cabelas.com/product/Hornady-Superformance-Varmint-Ammo/1139898.uts

And a cheaper option (not V-max, but a 50 gr. poly tip varmint pill):

http://palmettostatearmory.com/index.php/catalog/product/view/id/4550/category/53/

And you really need to learn what boutique means.

Glad you like it, I'm sure it will serve you well in that regard, as long as you don't need to hear or see after the fact.

You make a lot of assumptions. Have I ever said I'd shoot it unsuppressed, bare muzzle, or without ear protection?

As it were, I do not run a suppressor on it, but a Noveske KX3, which does a phenomenal job of reducing flash and directing blast forward. I also have ear pro hanging on the gun. A Glock 20 is my primary, but if I have time to get the ears on and get the rifle into action, it is a far more effective weapon than any handgun.

Do I feel the need to pick a 7.5" AR15 for home defense over other weapons I have? No.

Your prerogative.

 

[wally]

A 7" carbine in my front passenger seat gear bag beats

Have you ever shot a 7.5" 5.56 AR?

I'd not want to be in a vehicle shooting one! The muzzle blast and flash is impressive, certainly a part of their attraction, but limits the practicality of them. I like the way they handle, but the blast and noise, not so much.

 

[Hookeye]

Hmmmm, I thought the terms to be different,
Hydrostatic shock was the secondary wound cavity stuff.
Hydraulic shock was the old theory that such a wound would also pull on fluids in a network.

I do find it funny, how folks use ball ammo for hunting.

It might work, but I'd go with something designed for game. Wounding isn't an acceptable option when nuking critters.

.223 makes a dandy varmint round, there are a lot of "boutique bullets" out there...................geeesh.

From a rifle they do upset at 300 on critters weighing less than 20 lbs.

 

[Hookeye]

You want boom and flash, go SBR and add a "flash enhancer".
Did that on an indoor range.........my lane's "booth" contained much of it.
You feel the heat on your forearms.
Silly!

 

[MachIVshooter]

Hmmmm, I thought the terms to be different,
Hydrostatic shock was the secondary wound cavity stuff.
Hydraulic shock was the old theory that such a wound would also pull on fluids in a network.

https://en.wikipedia.org/wiki/Hydrostatics

Hydraulic is, of course, basically anything relating to fluids. Hydrostatic is the study of fluids at rest, fluid dynamics is the study of fluids in motion.

As it relates to small arms, the hydraulic shock, the fluid dynamics, of a high velocity body impacting a medium that is composed of fluids and tissues with high fluid content causes pressure. That pressure displaces fluids and tissue. It happens even with the lowest velocity rounds, but whit handgun bullets or other bullets traveling at lower velocities, the cavity is mostly temporary, save for inelastic tissues like the liver or brain. Hence, the wounding mechanism of low velocity rounds is mostly direct contact by the projectile or fragments thereof. Once you step into rifle velocities, the more elastic tissues are also stretched beyond their elastic limits, causing them to crush and tear. This is why rifle rounds are so much more devastating. If you use an expanding bullet, the frontal area is increased, displacing that much more fluid and tissue, creating an even larger crush cavity.

The magic 2,000 number is simply where we begin to see the kind of damage associated with rifle rounds. No, there is not going to be much difference in the wound created by a 1,900 FPS bullet and an identical one at 2,100 FPS. But 1,700 vs. 2,400? Yeah, the velocity makes a difference. That's why tiny bullets like the .17 Rem can cause such nasty wounds; it's an itty bitty bullet, but anything hitting you at 4,300 FPS is going to cause significant damage.

Now, there is the Dr. Courtney camp, who believe in remote damage caused by hydraulic shock resulting from bullet impacts, but it's mostly junk science, IMO. Yes, there will be hydraulic pressure effects throughout the body resulting from a ballistic impact, but enough to cause remote damage (such as hemorrhaging in the brain with a leg wound)? No. Sneezing generates more intracranial pressure than a bullet hitting somewhere else on the body.

 

[silicosys4]

https://en.wikipedia.org/wiki/Hydrostatics

Hydraulic is, of course, basically anything relating to fluids. Hydrostatic is the study of fluids at rest, fluid dynamics is the study of fluids in motion.

As it relates to small arms, the hydraulic shock, the fluid dynamics, of a high velocity body impacting a medium that is composed of fluids and tissues with high fluid content causes pressure. That pressure displaces fluids and tissue. It happens even with the lowest velocity rounds, but whit handgun bullets or other bullets traveling at lower velocities, the cavity is mostly temporary, save for inelastic tissues like the liver or brain. Hence, the wounding mechanism of low velocity rounds is mostly direct contact by the projectile or fragments thereof. Once you step into rifle velocities, the more elastic tissues are also stretched beyond their elastic limits, causing them to crush and tear. This is why rifle rounds are so much more devastating. If you use an expanding bullet, the frontal area is increased, displacing that much more fluid and tissue, creating an even larger crush cavity.

The magic 2,000 number is simply where we begin to see the kind of damage associated with rifle rounds. No, there is not going to be much difference in the wound created by a 1,900 FPS bullet and an identical one at 2,100 FPS. But 1,700 vs. 2,400? Yeah, the velocity makes a difference. That's why tiny bullets like the .17 Rem can cause such nasty wounds; it's an itty bitty bullet, but anything hitting you at 4,300 FPS is going to cause significant damage.

Now, there is the Dr. Courtney camp, who believe in remote damage caused by hydraulic shock resulting from bullet impacts, but it's mostly junk science, IMO. Yes, there will be hydraulic pressure effects throughout the body resulting from a ballistic impact, but enough to cause remote damage (such as hemorrhaging in the brain with a leg wound)? No. Sneezing generates more intracranial pressure than a bullet hitting somewhere else on the body.

Here is something I think you should read. I don't think you are correct in your assumption that rifle velocity equals large permanent wound cavities.
Hence the designs of many military loadings to yaw on impact.

http://www.frfrogspad.com/terminal2.htm

Look at the russian 5.45 round. Over three thousand fps impact speed, and no permanent wound cavity outside of the bullets own physical dimensions.

As for hydrostatic shock....Theory. No govt. agency or military uses "hydrostatic shock" as part of its criteria for small arms effectiveness.

 

[gotigers]

silicosys4

From what I can find, a 7" barrel will put a 55 grain pill out at under 2200 fps.
At that velocity, you'd better have boutique bullets to get any kind of expansion. At 2200 fps you won't have any fragmentation from any of the common fmj loadings.
What rifle bullets offer expansion down to 2200 fps, without blowing up at higher velocities?

Well, the TSX bullets (except the 53gr) and the 62gr Federal Fusion will expand below 2000 fps without blowing apart at higher velocities.

 

[MachIVshooter]

I don't think you are correct in your assumption that rifle velocity equals large permanent wound cavities.

It's not an assumption, and I said much larger, as in larger than handgun bullets of the same caliber. To simply say "large", I would have to include some sort of metric, which I have not. I've never stated that X rifle round at Y velocity produces Z size cavity. There are far, far too many variables to predict what the wound cavity of ANY round will look like in a human body, and it is even more difficult to estimate what the dimensions of the permanent cavity that exists after the temporary cavity has shrunk back down.

You also need to take those illustrations in the manner they're meant; an illustration. If you put a real bullet through real tissue, you will not see such channels in a cross section.

Hence the designs of many military loadings to yaw on impact.

The only one I can think of that is actually designed to yaw is the 7N6 5.45x39mm round, which is also the one you specifically cite as being ineffective. Hmmm.......

http://www.frfrogspad.com/terminal2.htm

Don't think I'd cite some dude's blog with a few C&P'd images from one of Fackler's reports. The report itself would be better, particularly if you read all of it, including sentences like:

Simply considering the dimensions of the human torso exposes the fallacy in bullet performance claims based on shots done in a 15cm block of tissue simulant

http://www.ar15.com/ammo/project/Fackler_Articles/effects_of_small_arms.pdf

As for hydrostatic shock....Theory. No govt. agency or military uses "hydrostatic shock" as part of its criteria for small arms effectiveness.

Again, hydrostatic shock is an oxymoron. And the wounding capacity of a bullet is almost never considered in military criteria; ability to penetrate certain armor at X number of meters always paramount. It was really a happy accident that 5.56mm rounds do what they do in the body. And LE looks primarily at penetration (FBI 12" requirement).

If you have access to the weapons, ammunition and targets, I suggest you have the effects of velocity demonstrated before your own eyes. We have a lot of rabbits out here, and I've shot them with everything from pellet rifles to .30-06, including numerous handguns and 5.56mm with both FMJ and expanding bullets. I can tell you that the destruction you see with M193, even from my 7.5" rifle, far exceeds what the 9mm, .45 ACP and even 10mm hollowpoints do. No, a 4 lb bunny is not a human torso. But it clearly shows in a very profound (and slightly macabre) way just how much more pressure is generated by the high velocity rounds.

Once more, for posterity, I have NEVER claimed that velocity is the only factor, or that expanding/fragmenting bullets don't do more damage. Of course they do, which is why I use them both for hunting and defense. Only a fool would think a bullet that maintains it's dimensions could create a wound comparable to that of an expanding projectile. But you would also be a fool to think that a pistol round, say, 9mm FMJ, could produce anywhere near the devastation that a FMJ rifle round, even a .224 cal at more modest mid-2K FPS velocities, will cause. Likewise for expanding bullets. If they did, our entry teams would still be rockin' MP5's, not Mk 18 10" 5.56mm rifles.

 

[Olympus]

Man, this hasn't been much help....

 

[gotigers]

Old Yesterday, 08:57 AM #1
Olympus

If they hold no practical purpose, why do they seem to prevalent?

they are fun flamethrowers at night or in indoor ranges.

otherwise useless.

 

[MachIVshooter]

Man, this hasn't been much help....

Your question has been answered more than once: Fun toys, and legitimate CQB/HD carbines with pros and cons.

Are you just seeking 50 replies affirming the same thing? If informative tangents bother you, I'm certain you can find a lot of mindless drivel over at arfcom. I would think it more valuable to understand why some of us choose the shorty ARs as HD weapons, rather than us just telling you we have.

 

[jmorris]

Just a silly question to begin with.

The shortest .223 I have is a 10.5" barrel, that was so I could have a .223 the same OAL as a 16" without all the noise. Why 10.5"? Because anything under 10" would void the warranty on the can.



What price do you pay cutting the barrel down? A round that runs 3200 fps out of a 16" is only going 2800 fps out of a 10.5" barrel, about the same at the muzzle as a round fired from a 16" is at 100 yards.

A 7.5" barrel would have the same round going 2200 fps or what the bullet is doing from a 16" barrel at about 225 yards.

If a .223 is useless at 225 yards out of a 16" barrel then it would be useless right out of the muzzle of a 7.5" gun.

On the other hand, I bet there are fewer "operators" that own AR's in any barrel length than not, so the only practical use one really needs is to make someone happy to own it.

 

[Tirod]

A round that runs 3200 fps out of a 16" is only going 2800 fps out of a 10.5" barrel, about the same at the muzzle as a round fired from a 16" is at 100 yards.

A 7.5" barrel would have the same round going 2200 fps or what the bullet is doing from a 16" barrel at about 225 yards.

There's the ballistics. It's better than a pistol caliber gun.

There are those who remark that the blast of a 7.5" AR would be horrendous in a vehicle. I have to ask, what makes a .45 ACP from a 5" barrel, or a .357 from an 3 1/2" any better? You do what you have to do. Survival first.

Of course, it presupposes that would be the only recourse you have, eliminating all the other options, such as evasion, seeing the situation ahead and avoiding it, etc. You are in a car.

And our soldiers do fire weapons from vehicles every now and then. Try sitting in a M103 with a .50BMG going off on the upper deck. You live thru it. You do suffer hearing loss, but you go home.

When you go home, you can have adequate protection for your family. Any handgun would be just as loud, some even more so. While most of us responding have pointed out 10.5" would be the better option, 7.5" has it's place and if some want to have that, it's their right.

Some like having open headers/no muffler on their Harley, and do it against the law. It's their choice. There's a lot more of them disturbing the peace than 7.5" AR pistols on a range any given day.

Boombox amps blasting away in the parking lot? Illegal in many cases, like the bikes, no enforcement. It's disturbing, it can happen anywhere. The 7.5" AR owners aren't in the lot popping caps, tho.

Give it some perspective. Some people shoot the .500 S&W. Those cost about double, have huge recoil, horrendous noise and blast. Who would go shooting with one of those? Well, youtube is full of videos.

There are a lot worst things than a 7.5" AR, and lacking any other input, I'm beginning to see the complaint is based on the gun - it's an AR.

Even from 7.5", 5.56 doesn't become a minor grade .22, and the noise and blast are not all that based on a level playing field. The numbers are there and the complaints aren't valid.

What was read as a source of information is wrong.

 

[jmorris]

There are those who remark that the blast of a 7.5" AR would be horrendous in a vehicle. I have to ask, what makes a .45 ACP from a 5" barrel, or a .357 from an 3 1/2" any better?

Faster burning powders. Same reason AAC will warranty 300 blk on a 7.5" barrel and not .223, the 300 uses pistol powders.

 

[benEzra]

To the OP's question about 7.5" ballistics, this might be helpful: http://www.sadefensejournal.com/wp/?p=1093

I have to ask, what makes a .45 ACP from a 5" barrel, or a .357 from an 3 1/2" any better?

.45 ACP out of a 5" barrel is about the same dB as a .223 out of an 18"-20" barrel.

A 7.5" .223 has as much or more gas pressure at muzzle exit as a .45 ACP would if the barrel were cut off a half inch in front of the chamber. A 5" .45 is far quieter.

A 7.5" AR is very likely as loud or louder than a .357 snubbie, which is in turn far louder than a 16" AR or a 4" 9mm or .45.

If I had the money I'd get one. A 7" carbine in my front passenger seat gear bag beats trying to unholster a pistol while wearing a seatbelt any day.

Actually, the holstered pistol will be far faster than even a 7.5" AR in a bag, and probably faster than a 7.5" AR lying on the seat, even if the AR were kept in Condition One.

As a gun to travel with, a 7.5" SBR would certainly be super handy to transport, though with a big penalty in blast and low-light muzzle flash.