Formula help - caliber x from barrel length y?

This is a discussion on Formula help - caliber x from barrel length y? within the Rifles forums, part of the Sniping Related category; Ok ballistics and math gurus, school me. Is there a forumula for figuring out a best guess if you plug in a caliber and weight ...

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  1. #1
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    Formula help - caliber x from barrel length y?

    Ok ballistics and math gurus, school me. Is there a forumula for figuring out a best guess if you plug in a caliber and weight given a certain barrel length to get an approximate velocity? Field tests with a chronic will always be better than a guess on paper. I know each barrel will have its own personality.

    The reason I'm asking is that I have a 300 wm, 308 and 30-06. I would like to hunt with an AR, because I can. I want to know the velocity and energy of a .338 federal out of the DPMS Lite Hunter now that they increased the barrel length to 20". It was 18". I don't want to get into an AR vs bolt gun discussion. I don't want to get into a .338 federal vs something else.

    Any experience with the .338 federal caliber, the DPMS Lite Hunter, or help figuring out what velocity to expect from that rifle is appreciative.

    I called DPMS and the rep I got said to look it up. Nice. Factory ammo velocities are usually a little inflated and probably done from a longer bolt gun barrel. I'd like to get as much info as possible before I commit to a new caliber.
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  2. #2
    Senior Member gsmithplm's Avatar
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    Re: Formula help - caliber x from barrel length y?

    Velocity is mainly a function of the bullet weight and the powder. Depending on how fast the powder burns and how much you use, your velocity will vary. Barrel length will effect it to some degree but that, again, depends on the powder and the charge.

    There's no pat formula. If you know what the approximate velocity for a given load is in a 26" barrel, you can guestimate what it will be in a shorter barrel. There are some studies that have been done but I don't have the numbers at hand.

    Ultimately, the only way you will know what it's going to do in your gun is to run it over a chronograph. And remember, temperature and pressure will effect velocity as well.
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  3. #3
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    Re: Formula help - caliber x from barrel length y?

    I guess that's what I figured, just hopeful. I know the best bet is to run the load I want over a chrony but I wanted to find out if, due to velocity, a given bullet would have the energy at range for elk.

    A friend of mine killed 4 bull elk over the years with an original SR-25, all 15 lbs of it. He was shooting a 165 Nosler Partition so I bet a .338 Federal will do just fine for elk out to 300 or so. Got to chrono it to make sure.

    I wanted the info so I could determine prior to buying a DPMS .338 Federal Hunter if it would work. I don't need another deer gun. I've got a Savage 06' for a wide range and .300 Blackout rifles for deer.

    Just wanted another AR, wanted a light AR for hunting, and wanted the best caliber for elk from an AR. The guy at DPMS said there was barely more recoil than the .308, and you had to know it was a .338 Federal to feel it. Like, more in your head than shoulder. I know the numbers say it's more, but I don't know how to properly calibrate my shoulder to duplicate the numbers.

    I think I can keep the rifle under 10 lbs with scope and rings. Hopefully!
    Ecclesiastes 10:2- The heart of the wise inclines to the right, but the heart of the fool to the left.

    Rights are what you have the freedom to do, not what you can GET FOR FREE!

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