18'' barrel velocity loss

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by okie man, Jan 3, 2014.

  1. okie man

    okie man Well-Known Member

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    I have a model 7 243win with a 18'' barrel. loaded up some 58 gr vmax bullets with 42 gr varget,cci primers. groups are well under a inch at 100 yards but have no idea of velocity. book quotes velocity with 24'' barrel. any way to get a idea on actual velocity without a chronograph?
     
  2. comfisherman

    comfisherman Well-Known Member

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    Well, if you trust the BC of the 58g v max as posted on the box. You could shoot at 100 yards, them move farther out and measure the drop at say 300 yards, compared to 100. Then pull up a web based ballistics calculator, and reverse calculate velocity. Handloads.com has one that would probably work for that, might take a little trial and error.

    I'd hazard 200-250 fps loss in an 18 inch tube. I have cut a 24 to a 18.5 in 243 and lost the low 200s on the light for caliber bullets like the 58.
     
  3. RT2506

    RT2506 Well-Known Member

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    My Sierra manual in the single shot pistol section list the 243 Win with a 15" barrel and gives 55 to 60 gr bullet with 41.7 grs Varget 3000 fps and with 43 grs 3100 fps.
    In the rifle section with the same bullets from a 22" barrel it gives Varget 41.9 grs 3500 fps and with 43 grs 3600 fps. So do the math and split the difference and it will get you close.
     
  4. jfseaman

    jfseaman Well-Known Member

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    ~25 FPS per inch but it starts go go up when you get shorter.

    There are articles on this.

    A Chrony is less than $100 and is a great tool to have.
     
  5. okie man

    okie man Well-Known Member

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    start adding up 100 dollar this and 100 dollar that and pretty soon it's a do I need it or like to have it thing. was trying to get a educated guess to put in the calculater. looking for something with less wind drift than my 223 . might not be worth burning 40+ grains of powder for a 58 grain 243 bullet.
     
  6. Dano1

    Dano1 Well-Known Member

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    If you're wanting a good varmit bullet for the .243 go to a 70-75g bullet, otherwise stick to the .223. I've shot quite a few 55g v-maxes and Nosler Ballistic tips out of my .243 Win Rem 700 VLS and the wind seems to slap them around for shots further than 300yds anyway.

    Velocity loss is quite a bit when dealing with a shorter bbl as the others have already stated. You can actually load a 55g bullet to 4000fps out of a 26"bbl, but I'd dare say that you're probably around 3100-3150fps with 42g of Varget, you can get it to 3350fps with 45g if it still will shoot....

    H4895 will get them to 3500fps with 44.5g out of your rifle, if you are willing to shoot that much powder.

    Hope this helps,

    Dan

    P.S. Hodgdon.com has data for the .243 Win for pistol loads, look them up. They are usually figured for a 16" or less bbl....