Necking up or down velocity change?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by midwesthunter, Jul 27, 2010.

  1. midwesthunter

    midwesthunter Well-Known Member

    Feb 28, 2008
    I was wondering if you neck a cartrige down can you still get same ballistics for same weight bullet? Or does the smaller neck size restrict this?
  2. Varminator 911

    Varminator 911 Well-Known Member

    Dec 7, 2007
    Generally you're going to get less velocity because there is less area for the gas pressure to push on. Pressure in the barrel would be about the same using optimum powder. But the bullet has less cross sectional area for that pressure to act on. The difference won't be much if you compare something like 7mm to 6.5 mm. But if you compare 224 or 6mm to 7mm or 308, the difference begins to add up.

    For long range you also need to factor in bullet SD and effects on BC of the bullet. That gets more complicated. But in general I still think you generally come out ahead with the larger bore unless you are talking a small case. For long range you need to factor in caliber, bullet weight, case size, and available bullets.

    If you could give some idea what two calibers and case size you are considering, you might get a better answer.
    Last edited: Jul 27, 2010