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.223: Velocity loss going from 20" to 18"?

Discussion in 'Rifle Country' started by Mylhouse, Aug 14, 2003.

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  1. Mylhouse

    Mylhouse Member

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    I'm sure this has been discussed before, but my search skills are lacking.

    I'm thinking of a 1 in 8" twist .223 AR bull barrel upper with a 18" tube for prairie doggin and target.

    For those of you that have spent some time behind a chrono, what kind of velocity loss does the 18" AR15 barrel suffer when compared to a 20" tube with 55gr, 62gr, and 75gr loads?

    Reason I ask is I can get an 18" upper NOW, or if I hold out for a few weeks, then I can get the 20" if the difference is significant.

    Thanks
     
  2. Kharn

    Kharn Member

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    I think its about 50fps less per 1" of barrel lopped off for 62 and 55gr loads.

    Kharn
     
  3. geekWithA.45

    geekWithA.45 Moderator Emeritus

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  4. Mylhouse

    Mylhouse Member

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    Thanks guys!
     
  5. Art Eatman

    Art Eatman Administrator Staff Member

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    Yeah, Kharn's sure close enough for government work.

    :), Art
     
  6. larryw

    larryw Member

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    Quickload's a pretty handy bit of software. This is what it came up with:

    223 Rem
    55gr SPBT
    26gr of 748
    18" bbl 2896fps
    20" bbl 2980fps

    223 Rem
    62gr FMJ
    24gr of 748
    18" bbl 2735fps
    20" bbl 2811fps

    223 Rem
    75gr BTHP
    23gr of 748
    18" bbl 2560fps
    20" bbl 2628fps

    Refer to loading manuals. DO NOT USE THESE LOADS!!! They are software simulations for velocity comparisons only.
     
  7. Mylhouse

    Mylhouse Member

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    I appreciate you running those figures through your software program for me, Larry.

    So are those numbers from the 55gr bullet enough to disintegrate prairie dogs?:evil:

    Thanks again, everyone.
     
  8. WonderNine

    WonderNine member

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    From what I understand the 55gr .223 bullet reliably fragments at anything above 2500 fps (or was it 2700?), so using the lighter stuff should work.

    I used to want a Romanian SAR-3 (.223 AK), but I think the velocity loss out of the 16" barrel (compared to a normal 20") is just too much to make it anything other than a glorified .22 magnum.
     
  9. Zak Smith

    Zak Smith Moderator Emeritus

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    These numbers seem a bit low for a 20" barrel.

    Modulo the 5.56 vs. .223 chamber issue, standard M193 (55gr FMJ) shoots about 3200-3250fps from a 20", and M855 (aka SS-109, 62gr FMJ/Penetrator) shoots about 3100fps from a 20".

    -z
     
  10. Poodleshooter

    Poodleshooter Member

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    I know it's not what you asked, but I love butting in....
    A 1 in 8" twist isn't the best for shooting lightly constructed 40-55gr hollow point bullets. Many 1x7"s will blow varmint bullets up (mine destroys any non-Vmax soft or hollow point bullet that exceeds 2800fps , and I know of at least 1- 1x8"twist barrel owned by a fellow at my range which refuses to shoot softpoints.
    It's often not an option for the lower priced barreled uppers unfortunately, but a 1x9",1x10" or even 1x12" would better serve a varmint hunter.
    That said, I'd wait and get the 20", or even longer (my personal preference will be for a 22" or 24" barrel when I get around to buying a new upper.
     
  11. WonderNine

    WonderNine member

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    What would a .223 do out of a 16" barrel?
     
  12. Zak Smith

    Zak Smith Moderator Emeritus

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    WonderNine,

    Here's some actual chrono data from my RRA 16" (1-in-9):

    Black Hills 68gr "blue box": 2670fps
    South African M193 55gr surplus: 3060fps
    Hornady TAP 60gr: 2914 fps
    IMI M855 62gr: 2958fps
    Black Hills 55gr "blue box" was about 2870fps

    -z
     
  13. WonderNine

    WonderNine member

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    I love the SA surplus stuff for cheap plinking and it's been totally reliable, I'd load it into a self defense rifle. I don't know if it's the most accurate round in the world though if you know what I mean.... What has been your experience with it as far as accuracy?

    Btw, I was guessing that it was doing about 3400 fps out of my father's 20" bolt action .223 Winchester 70, I think I was right....they sure are loud and loaded hot.

    3060 fps is not bad at all...maybe I will get that SAR-3....I can't decide...

    Are the 30 round mags for the SAR-3 smaller and lighter than the SAR-1? That would make it easy to carry more ammo. I understand Interordinance has the correct mags for it.
     
  14. larryw

    larryw Member

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    Zak, like I said, these aren't actual loads, these are computer simulations for the sole purpose to compare muzzle length velocity losses. I chose a "223" powder from a pulldown menu, grabbed a couple bullet profiles from a menu and "added" powder until I got to similar lowish pressures (because I know someone may ignore the warning and use this as load data. ;) ).
     
  15. Zak Smith

    Zak Smith Moderator Emeritus

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    At 200 yards, I get about 2 - 2.5 MOA with the SA surplus, from a 16" AR. I'm not sure how much of that is me, except that I have shot 0.5MOA groups at 100 yards with different ammo.

    -z
     
  16. WonderNine

    WonderNine member

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    Hmm, I was probably just having a crappy day at the range then or the scope was off, I dunno.

    I was getting 3" @ 100 yards with the SA surplus in the Winchester model 70 while the Black Hills ammo easily did sub 1". Maybe I was getting tired, I shot the SA at the end.
     
  17. Zak Smith

    Zak Smith Moderator Emeritus

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    3" @ 100 yards isn't so far off from the 2.5 MOA I mentioned.

    -z
     
  18. WonderNine

    WonderNine member

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    Oh, for some reason I thought you had said 2-2.5 @ 200 yards..
     
  19. WonderNine

    WonderNine member

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    Oh wait, you did...
     
  20. Mylhouse

    Mylhouse Member

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    Thanks for butting in, Poodleshooter. I'll take all that into account...
     
  21. Rattler

    Rattler Member

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  22. Zak Smith

    Zak Smith Moderator Emeritus

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    MOA/Inch confusion?

    I mentioned 2 - 2.5 MOA at 200 yards, which is about 2-2.5" at 100yards, or about 5-6" groups at 200 yards - which is the result I got. So I figure the SA surplus is good for "minute of pie plate" at 200 yards.

    -z
     
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