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7.5" Barrel AR-15s

Discussion in 'Rifle Country' started by Olympus, Aug 30, 2015.

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  1. Tirod

    Tirod Member

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    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.
     
  2. Olympus

    Olympus Member

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    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.
     
  3. MachIVshooter

    MachIVshooter Member

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    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.

    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.



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

    Never asserted such a claim. Stop making strawmen.

    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? :rolleyes:

    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.


    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?

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


    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/

    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.

    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.

    Your prerogative.
     
    Last edited: Aug 31, 2015
  4. wally

    wally Member

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    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.
     
  5. Hookeye

    Hookeye Member

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    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.
     
  6. Hookeye

    Hookeye Member

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    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!
     
  7. MachIVshooter

    MachIVshooter Member

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    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.
     
  8. silicosys4

    silicosys4 Member

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    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.
     
    Last edited: Aug 31, 2015
  9. gotigers

    gotigers Member

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

    MachIVshooter Member

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    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.

    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.......

    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

    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.
     
    Last edited: Aug 31, 2015
  11. Olympus

    Olympus Member

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

    gotigers Member

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    they are fun flamethrowers at night or in indoor ranges.

    otherwise useless.
     
  13. MachIVshooter

    MachIVshooter Member

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    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.
     
  14. jmorris

    jmorris Member

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    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.

    jeepm.jpg

    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.
     
  15. Tirod

    Tirod Member

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    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.
     
  16. jmorris

    jmorris Member

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

    benEzra Moderator Emeritus

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

    .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.

    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.
     
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