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Estimating Velocities for Changed Loads and Barrel Lengths

Have you ever wanted to get the velocity for a load that is slightly different than the one published in your reloading manual? For example, you’re loading for a 10″ barrel pistol in .223 Remington and are using 52 gr bullets. You would like some idea of the velocity, but the only load data for the bullet weight is for 22″ barrels. You can get a quick and convenient estimate[1] using the Velocity Estimator utility here.

Information you will need for your particular question is:

  • For the load data you have:
    • Bullet weight and diameter,
    • Case length and volume[2] (grs of water completely filling the case),
    • Powder charge weight,
    • Barrel length,
    • Muzzle Velocity.
  • You’ll need only three added pieces of information[3] for your situation:
    • Bullet weight,
    • New charge weight,
    • New Barrel Length.

Choose one of these pre-filled forms to get started. Use the “Change Reference Load Values” button in any of these to enter the starting data for your cartridge if it isn’t in this list.

Start with the 6.5 Grendel
Start with the .223 Remington
Start with the .243 Winchester
Start with the .308 Winchester

Start with the .357 Magnum
Start with the .45 Auto

Remember that a lot of factory ammunition has a standard deviation in velocity of 35 ft/sec and that reloaded ammunition typically runs as much as 50 ft/sec. The results are shown as a range based on the standard deviation of assumed independent measurements for the factory ammunition. (Yes, your reloads are being given credit for being better than average!)

[1] The estimator uses a modified form of the Powley Ballistic Calculator. The modifications permit estimates for less than nominal full loads and using effectively any powder. This is in contrast to the original Powley constraints limiting us to more or less full loads using IMR powders.

[2] Case volume is not available in many, if not most, reloading data sources. has a comprehensive and growing set of reloading data, including the cartridge volume. The site, however, requires being a member to access the portion of database that has case volume. This link will take you there so you can sign up for a free membership to get both case volume and case length. You can also upgrade to a paid subscriber status to access an excellent set of reloading data.

[3] Safety is in your hands, and we cannot take any responsibility for your choices of load. Be aware that the reloading literature tells us there are some instances where severely reduced powder charges can be dangerous to you and your firearm. Be sure to check your powder and cartridge references before using any loads less than any published data.

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