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Barrel Length and Bullet Velocity Ratio

 
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  #8  
Old 05-08-2013, 10:34 AM
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Re: Barrel Length and Bullet Velocity Ratio

Quote:
Originally Posted by CB11WYO View Post
Just too many variables to work with, too many gun "personalities" in the mix I guess.
CB11WYO,

No, that's not what I was saying. You can get some very good ideas about what will happen in specific instances, when you're talking about a given caliber, a particular bullet weight and a certain powder. In your original post, the question you asked was just asked too broadly. You CAN get a pretty good idea of what barrel length variations will do to a load, but you need to be very specific about the components involved in that particular instance. Simply saying that an increase of X will increase or decrease velocity Y fps (regardless of caliber, bullet weight, etc., etc.,) just can't be answered accurately.

Hope that clarifies it a bit, and didn't mean to discourage you from asking.
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  #9  
Old 05-08-2013, 11:02 AM
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Re: Barrel Length and Bullet Velocity Ratio

This is a good read for those that haven't.

Lilja Precision Rifle Barrels - Articles: Barrel Lenghts and Velocities in the 338/378 Weatherby Magnum
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  #10  
Old 05-08-2013, 03:13 PM
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Re: Barrel Length and Bullet Velocity Ratio

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Originally Posted by Kevin Thomas View Post
CB11WYO,

No, that's not what I was saying. You can get some very good ideas about what will happen in specific instances, when you're talking about a given caliber, a particular bullet weight and a certain powder...
That's a little more what I was after...

Like say I'm loading for a 7mm Rem Mag, using 180 gr bergers and Retumbo. Say reloading manual brand "X" says my load will do 2900 fps from a 26" barrel, but I'm shooting a 28" tube... what kind of increase should I be looking for? Etc, etc...

(yes in the end I can just validate my velocity using trajectory anyway...)
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  #11  
Old 05-08-2013, 03:29 PM
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Re: Barrel Length and Bullet Velocity Ratio

Like we said before that is a totally variable question. Logic says a 80-100 fps increase but there is no way to say for sure. It may be no velocity change at all.
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  #12  
Old 05-08-2013, 04:12 PM
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Re: Barrel Length and Bullet Velocity Ratio

Another example I have for you is my wifes 7mm rem mag. It is a tikka with a 24" barrel. According to my book the load she shoots should be around 29-2950 with a 162sst. That gun bearly breaks 2800fps. The same load in my old savage shot nearly 3100 with the same length barrel. Not sure how exactly it works but there are fast barrels and slow barrels. Hope this is helpful. But probably not.
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  #13  
Old 05-09-2013, 06:32 AM
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Re: Barrel Length and Bullet Velocity Ratio

Quote:
Originally Posted by CB11WYO View Post
That's a little more what I was after...

Like say I'm loading for a 7mm Rem Mag, using 180 gr bergers and Retumbo. Say reloading manual brand "X" says my load will do 2900 fps from a 26" barrel, but I'm shooting a 28" tube... what kind of increase should I be looking for? Etc, etc...

(yes in the end I can just validate my velocity using trajectory anyway...)
I shoot longer barrel than the loading data I'm using. Working up my loads I see an increase in velocity with my start loads and most times I'm at published velocity gr or two under max load.

Nosler start load for the 280AI with 26" long barrel was 57.5gr/IMR-7828 @ 2856fps with 160gr AB that same start load in my 27" long barrel was @ 2916fps which was gain of 60fps with 1" more barrel.

One of my 30-06 was playing around with some of Hodgdon data using H-4350 and 150gr E-Tip their barrel was 24" long mine was 25". their max load was 57.8gr/H-4350 @2927fps and my max load was 58gr @ 2998fps. Another 30-06 with 26" long barrel with 180gr Partition max in Nolser data is 2825fps I can run that easy 100fps more with varies loads.

I build a 300WSM with 26.5" long barrel and it's easy getting that extra velocity. I have pretty good list on gains with some of my barrels but in the end I stay pretty close to max velocity and nice to know don't need max powder. 30yrs ago when I was in my 40 looked at velocity little different. Well good luck
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  #14  
Old 05-09-2013, 04:07 PM
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Re: Barrel Length and Bullet Velocity Ratio

CB11WYO,

Okay, I an this on QuickLoad, with the component combination you cited; Retumbo, Berger 180s in a 7mm Mag with a 26" and a 28" barrel. It showed a difference of about another 50 fps in the longer barrel, or about 25 fps per inch. This is about what I would have figured, but it could well change a bit with a different powder, different charge weights, etc.. As I said, it isn't linear, and will change with the variables in play. Ballpark figures of 20-40 fps per inch is usually the figure that gets bandied about, and it's roughly correct.

Bottom line is, no matter what an interior program like QL says, it's the chronograph that will give you the final answer. Hope that helps.
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