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Thread: 7.5 vs. 10.5

  1. #1
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    7.5 vs. 10.5

    I've decided my next purchase will be a SBR. Is there much of a reliability issue with the 7.5? I've bought Noveske in the past and have spoken with them about this issue but would like to hear from someone who shoots one. I've also chronoed 20, 16, 14.5, and 10.5. How much more loss would you expect with the 7.5? I've considered just buying the stripped lower and submitting my own paperwork and then buying the upper. For those that have done that can you include the various lenghts on the form without actually owning them yet so you can put whatever you want on the lower?

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    Cool Shorty SBR's...

    Quote Originally Posted by seb5 View Post
    I've decided my next purchase will be a SBR. Is there much of a reliability issue with the 7.5? I've bought Noveske in the past and have spoken with them about this issue but would like to hear from someone who shoots one. I've also chronoed 20, 16, 14.5, and 10.5. How much more loss would you expect with the 7.5? I've considered just buying the stripped lower and submitting my own paperwork and then buying the upper. For those that have done that can you include the various lenghts on the form without actually owning them yet so you can put whatever you want on the lower?
    I have always turned in my papers for SBR's w/ the shortest length barrel I ever intend to install...
    You can have that length or longer mounted, legally, w/ your document...

    ('Also, the shorter the barrel/ system, the better for headaches w/ a gas impingement system...)
    I use piston drive; solves that 100%

    E!

    PS - I do installs/ builds w/ Adams Arms systems...
    Drop me a note if you need something built, or just say Hi...

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  3. #3
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    Steve Troy built me a 7.5" M7A1 this past January. It's perfectly reliable and fun to shoot. Steve uses nothing but the best. I had the honor and privelage to assist him assemble it at his shop.

    Believe it or not, against all adversity, there are still some great manufacturers, gun dealers and 2nd Amendment supporters in the Peoples Republic of Massachusetts.

    http://www.troyind.com/m7a1.html




    Mike Butler

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    A good friend of mine had a Noveske 7.5" and it ran like a top with even the cheapest of ammo. It was a hell of a lot of fun and didn't appear to be any louder or concussive than my 10.5".

    On one hand you'll catch a lot of flak about how "it doesn't get enough velocity to fragment" but I'd recently heard that it only barely stabilizes most bullets so that may have a positive effect on ballistics.

    The only medium I'd shot it into was pumpkins with wolf ammo and it ripped a nice sized chunk out of the back ends.


    As for lengths on forms, I've heard that once short barreled you can run practically anything. I've also heard that you REALLY want to insure that you're within the law and send the ATF a fax stating that you're changing lengths permanently. I'll get you the lengths I put down on my 10.5" when I get home today.

  5. #5
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    Quote Originally Posted by erh View Post
    I have always turned in my papers for SBR's w/ the shortest length barrel I ever intend to install...
    You can have that length or longer mounted, legally, w/ your document...
    There is nothing in the NFA that states what you have stated above. As far as the letter of the law goes, you can have whatever length barrel you want on any registered SBR. The ATF asks that you notify them if you permanently change the configuration but it is not required. Any advice to the contrary is your opinion and while it may be prudent it is also not necessary.

  6. #6
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    Question

    So does anyone have any velocity stats on a 7.5" setup with some of the more popular ammo choices (M855, M193, etc)?

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    Both my SBRs are listed as having 10.5-inch barrels. But when I talked to the ATF NFA Branch they recommended that I send them a letter informing them of any changes or additional caliber or configurations (i.e.: barrel length). FWIW.
    We must not believe the Evil One when he tells us that there is nothing we can do in the face of violence, injustice and sin. - Pope Francis I

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    Quote Originally Posted by 9mmkungfu View Post
    So does anyone have any velocity stats on a 7.5" setup with some of the more popular ammo choices (M855, M193, etc)?
    Here's some velocity data published by MSTN on another forum. The date ranges from 7.5" to 20" for comparison:

    MK 262 VELOCITY DATA
    __________________________________


    7.5" 2053 FPS ... 10.5" 2363 FPS
    DIFFERENCE 310 FPS
    DIFFERENCE/INCH 103 FPS

    10.5" 2363 FPS ... 14.5" 2576 FPS
    DIFFERENCE 213 FPS
    DIFFERENCE/INCH 53 FPS

    14.5" 2576 FPS ... 16" 2669 FPS
    DIFFERENCE 93 FPS
    DIFFERENCE/INCH 62 FPS

    16" 2669 FPS ... 18" 2769 FPS
    DIFFERENCE 100 FPS
    DIFFERENCE/INCH 50 FPS

    18" 2769 FPS ... 20" 2818 FPS
    DIFFERENCE 49 FPS
    DIFFERENCE/INCH 25 FPS



    M855 VELOCITY DATA
    __________________________

    7.5" 2244 FPS ... 10.5" 2639 FPS
    DIFFERENCE 395 FPS
    DIFFERENCE/INCH 132 FPS

    10.5" 2639 FPS ... 14.5" 2861 FPS
    DIFFERENCE 222 FPS
    DIFFERENCE/INCH 56 FPS

    14.5" 2861 FPS ... 16" 2938 FPS
    DIFFERENCE 77 FPS
    DIFFERENCE/INCH 51 FPS

    16" 2938 FPS ... 18" 3046 FPS
    DIFFERENCE 108 FPS
    DIFFERENCE/INCH 54 FPS

    18" 3046 FPS ... 20" 3061 FPS
    DIFFERENCE 15 FPS
    DIFFERENCE/INCH 7.5 FPS


    XM193 VELOCITY DATA
    _________________________________


    7.5" 2364 FPS ... 10.5" 2755 FPS
    DIFFERENCE 391 FPS
    DIFFERENCE/INCH 130 FPS PER INCH

    10.5" 2755 FPS ... 14.5" 2984 FPS
    DIFFERENCE 229 FPS
    DIFFERENCE/INCH 57 FPS PER INCH

    14.5" 2984 FPS ... 16" 3075 FPS
    DIFFERENCE 91 FPS
    DIFFERENCE/INCH 61 FPS

    16" 3075 FPS ... 18" 3245 FPS
    DIFFERENCE 170 FPS
    DIFFERENCE/INCH 85 FPS

    18" 3245 ... 20" 3254 FPS
    DIFFERENCE 9 FPS
    DIFFERENCE/INCH 4.5 FPS
    Last edited by No Bananas; 11-29-08 at 17:10.
    Have Fun, Be Safe

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    You may want to examine what you will actually be using this rifle for. There are several very reliable manufactures as stated above that can build you very reliable firearms in 7.5" configurations. That being said, this short of a barrel is not well suited for engaging targets at even a moderate range that may be shooting back. Bullets need at least 2000 fps to reliably fragment and that does not leave much room for error in this length configuration. Once you introduce the issue of barrier penetration as well you are limited even further. 10-10.5" is the shortest recommended length for duty use and then with the understanding that your real world effective range is 100 yards or less. Two way ranges change things. Good luck.
    Last edited by Broadway; 12-02-08 at 21:08.

  10. #10
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    Wink

    Quote Originally Posted by b_saan View Post
    There is nothing in the NFA that states what you have stated above. As far as the letter of the law goes, you can have whatever length barrel you want on any registered SBR. The ATF asks that you notify them if you permanently change the configuration but it is not required. Any advice to the contrary is your opinion and while it may be prudent it is also not necessary.
    I wasn't aware that I sounded as though I was quoting anything...
    But... I've been known to try to be the Master of the obvious upon occasion as well Bud...

    E!
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  11. #11
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    One other thing to consider (I'm going to stay out of the velocity/effectiveness discussion for now) is that many suppressor companies won't warranty their 5.56 cans when installed on a barrel less than 10.5". Not sure if that is a concern for you, I've just seen too many posts on Silencertalk from owners that bought the gun first and THEN discovered the warranty issue.

    Personally, I'd go 9mm for a 7.5" and 5.56 for a 10.5".

  12. #12
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    OK, I will say, or ask, this much about velocities. Anyone know if these numbers are correct? They look about right to me.

    M193 impact velocity in human tissue for reliable fragmentation 2700 fps
    M855 = 2600 fps
    Mk262 = 2200 fps

  13. #13
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    Quote Originally Posted by rob_s View Post
    One other thing to consider (I'm going to stay out of the velocity/effectiveness discussion for now) is that many suppressor companies won't warranty their 5.56 cans when installed on a barrel less than 10.5". Not sure if that is a concern for you, I've just seen too many posts on Silencertalk from owners that bought the gun first and THEN discovered the warranty issue.

    Personally, I'd go 9mm for a 7.5" and 5.56 for a 10.5".
    I agree. My first foray into short barreled ARs (aside from my M4) was a Mk. 18 I got to try in Iraq. While the muzzle blast is there it was not at all unbearable and kind of fun. I thought the 7.5" would be cool until I fired a co-workers 7.5" AR pistol...I was not amused. Even with a Noveske KX3 the muzzle blast was outrageous. On the other hand a 7.5" 9mm should be very pleasant even without a can.

    I would agree, I think the absolute shortest I would go on a 5.56 barrel is 10.5 (I would prefer 11.5), but a 9mm I would go down to 5.5 even.
    It's an M112 block of C4...

  14. #14
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    I would suggest 12.5 inches. That is a nice length. I would never go under 10.

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    Quote Originally Posted by AJNAC4FL View Post
    Steve Troy built me a 7.5" M7A1 this past January. It's perfectly reliable and fun to shoot. Steve uses nothing but the best. I had the honor and privelage to assist him assemble it at his shop.

    Believe it or not, against all adversity, there are still some great manufacturers, gun dealers and 2nd Amendment supporters in the Peoples Republic of Massachusetts.

    http://www.troyind.com/m7a1.html




    Mike Butler
    I have one of those one it's way to me. I'm excited :-)

  16. #16
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    Would rather have a 10.5 with A2 than a 7.5 with KFH.

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    Just FYI man, I finally got out to the range today with my new BCM 11.5" upper with the DD 10" rail and man-oh-man was it nice!! I really don't think you can go wrong with it at all. VERY nice! Damn good quality and outstanding accuracy too!

    Just order the 11.5" upper, a F/A BCM bolt carrier group and some front and rear back up irons and you're ready to rock!

    My friend recently purchased a 7.5" upper. It was really fun to shoot and all (****ing loud!), but I would ONLY purchase a 7.5" SBR if I ALREADY had one or two other SBRs (and I just might in the future), as the 7.5" is just not as practical, useful, effective or reliable as the other longer length barrels (as others have stated millions of times on this forum).

    This is all just my opinion however, you are completely free to buy whatever you'd like, as it's your $$$ not mine!

    But seriously brother, do yourself a huge favor and just buy a 10.5" LMT or 11.5" BCM or Colt.
    Last edited by RetreatHell; 07-03-09 at 22:13.

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    RyanB: I would rather have a 7.5" with a Smith Vortex then a 7.5" with a KFH. I had a Noveske KFH on my 7.5" for a couple of years and while it does direct the concussive blast forward you still get a big fireball. I now run a Smith Vortex and it has absolutely zero fireball in daylight and has eliminated the same fireball by about 98% at night. Concussive blast feels less to the shooter with the Vortex but I certainly wouldn't want to be standing next to, or to the side of the muzzle.

    MadDog
    Last edited by MadDog; 07-09-09 at 15:12.

  19. #19
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    Quote Originally Posted by rob_s View Post
    Personally, I'd go 9mm for a 7.5" and 5.56 for a 10.5".

    Same here. I think anything shorter than 10.5 in 5.56 is silly nonsense. I really don't even like going as short as 10.5. I'm an 11.5 fan.

  20. #20
    Anyone tried the Norma 55g lead tip? No problems of "fragmentation" this mommy will keep it all together ... and just will tear the sh*t out of your target!
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