SBR opinions

Discussion in 'AR-15 Discussion' started by Tenderribbs, May 29, 2012.

  1. Tenderribbs

    Tenderribbs New Member

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    I have noticesd myself giving the SBR a little more attention than usual . I'm really liking the look of the rifle. I have a 11 1/2 in on my DPMS with a 5 1/2 FS . Would you cut and rethread the barrel or just get new barrell .Are mist SBR flat top At15? And of course get your tax stamp before any of the above happend.
     
  2. Sniper03

    Sniper03 Supporting Member Supporter

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    I would just get a new barrel. I am sure that you are aware that once it becomes a registered SBR it is always an SBR!

    03
     

  3. Tenderribbs

    Tenderribbs New Member

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    Yes but is that Bad thing ?do you think it's devaluing the gun?
     
  4. JonM

    JonM Moderator

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    its not a bad thing in and of itself but it does revalue the lower receiver to 0$. there is no resale value of a sbr lower. its engraved(federal requirment) with your information. it cannot be resold.

    even if you could no one is going to pay 200$ (nfa transfer tax) + the cost for a used lower. they are just going to register their own new one.

    going shorter than 14.5 on a 556/223 rapidly drops that cartridge somewhere around 22magnum levels. if your going to go shorter than 14.5 i would go 9mm 40sw or 45acp
     
    Last edited: May 29, 2012
  5. AgentTikki

    AgentTikki New Member

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    Or 6.8 spc or 300 aac blackout.
     
  6. xRacerX75x

    xRacerX75x New Member

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    I guess I'm not understanding what you mean by it "rapidly drops the cartridge somewhere around 22magnum levels", please explain.
     
  7. pagj17

    pagj17 New Member

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    Because of the short length of the barrel the powder doesn't burn completely reducing pressure and therefore velocity. It may look cool but it's ineffective past 100 yards or so.
     
  8. xRacerX75x

    xRacerX75x New Member

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    Ok makes sense but for a patrol rifle application? Clearing houses and buildings which create distances from point blank to maybe 10 or 15 yards(in a small warehouse) a 5.56 SBR would fill the roll well right?
     
  9. JonM

    JonM Moderator

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    Your better off with a 12ga shotgun and a sidearm. But yeah it would work ok at that range
     
  10. Tenderribbs

    Tenderribbs New Member

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    My barrell is already 11 1/2 in iit
    Has a 41/2 FS are you saying it has the lethality of. 22 magnum?
     
  11. triggerjob

    triggerjob New Member

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    Yes thats what he is saying. Basically, any powder that burns after the bullit leaves the barrel is wasted. The shorter the barrel the less time for the powder to burn. Conversly, any barrel lenth added past the point of powder expansion, slows the bullit down. So the trick to maximising bullit energy is to have the bullit exit the barrel at the instant before, max pressure.

    You can clock your round, using diferent barrel lenths and as you shorten a barrel, velocity will drop off, conversly as you lenthen a barrel to far velocity will drop off.
     
  12. AgentTikki

    AgentTikki New Member

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    I think a 12 in barrel will be adequately long enough to keep velocities above the optimum fragmentation speed for 5.56 at cqb distances. If you are going to rebarrel, look into .300 blackout.
     
  13. Tenderribbs

    Tenderribbs New Member

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    That seems to be the thing these days is the 300 BO. Haven't checked the price difference on the ammo .
     
  14. MikeJK

    MikeJK New Member

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    I need to get the BLK out again. Ammo is down to $10.99 a box which is good for what it is.
     
  15. AgentTikki

    AgentTikki New Member

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    where? link! link!
     
  16. purehavoc

    purehavoc New Member

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    I wouldnt say its at .22 mag levels the difference between a 7.5" barrel and a 20", both .223 is roughly 430 fps at the barrel and roughly 600 fps at 80 M, sighted in at 50 yards still hits 10" steel plates at 100 yards . Now further than that its lost a ton of velocity and falls off pretty quick . I need to run it thru my chrono with some 5.56 and see how much difference there is between it and the standard .223 FMJ ammo on the velocity. Shortys have their special place of use and most cant justify the need or the want to spend the $200 for the stamp when they can get basically the same thing in a pistol with out jumping through the hooplah and the wait
     
  17. KingTiger

    KingTiger Member

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  18. MikeJK

    MikeJK New Member

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    The .300 BLK guys posted some 125gr for $10.50 on FaceBook a couple days ago as well. I thought it was from CTD but can't find it now. I'll check FB.
     
  19. AgentTikki

    AgentTikki New Member

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    I'm not really agreeing with the numbers you are posting here.
    Optimally fragmentation occurs at velocities above 2700 fps.
    Muzzle velocity for M193 55 gr fmj is in the 3200 fps range with a full length barrel.

    430 fps is a really fast paintball.
    250-1000+ for pellet guns.
    230 gr fmj .45 acp shoots in about the 900 to 1000 fps depending on barrel length.

    Um here you go....
    http://www.ar15.com/content/page.html?id=213

    Once you go under 2700fps, fragmentation gets really spotty so for the most part you are just punching holes. But much deeper holes than a .22 magnum. :rolleyes:
     
  20. MikeJK

    MikeJK New Member

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    They have developed 300 BLK that is designed to work at subsonic levels.