Is there a formula?

Wingy

Well-Known Member
Ok I'm sure someone here will know how this works before I go and mess up a rifle.

If I shorten the barrel length then I know the muzzle velocity will be reduced (if the only thing changed is barrel length)

So is there a formula that can be applied to work out the effect?

E.g.
Barrel length (x) = velocity (y)
Barrel length (x-1) = velocity (y-1)
And so on

If feasible then I could possibly play around with load development to regain the lost velocity if required
Wingy
 

nun_hunter

Well-Known Member
There are plenty of articles on the Web charting velocities and barrel length. There are some variables regarding calibre/bullet weight and magnums etc. Generally though they do fall under 50fps/inch with some losing a lot less than that.
 

Wingy

Well-Known Member
From another thread
Thanks for that some interesting reading. I've been thinking of chopping my .243 for a while but didn't want to loose too much accuracy or velocity. Then a mate at work asked as he is considering chopping his air rifle (he's into his targets)
I didn't think there would be a be all end all formula as too many variables.
 

shooternz

Well-Known Member
Formulas are all an educated guess the only way to know is to chop your barrel all barrels are a law unto them selves, chromo your load then work on the biggest loss predicted
the .243 is only just making require energy levels in most cases you may well make it illegal for deer in some places
 

Wingy

Well-Known Member
Formulas are all an educated guess the only way to know is to chop your barrel all barrels are a law unto them selves, chromo your load then work on the biggest loss predicted
the .243 is only just making require energy levels in most cases you may well make it illegal for deer in some places
That's exactly why I wanted to do the calculation before chopping it.
 

JabaliHunter

Well-Known Member
A formula would be based on empirical tests. The problem is that it will vary by powder burn rate and pressure, as well as bullet weight.

I wouldn't expect it to be linear from muzzle to chamber either, although the difference may make no practical difference for us
 

antsa

Well-Known Member
I went through a lot of articles about this and after a bit of scribbling and some amateur statistics settled on 3m/s per cm length change. Good enough for me within the range of lengths I work with - 20 to 24 inches. Too many variables involved here.

Cheers
 

ileso

Well-Known Member
you would have to apply mathematics to figure it out, and then it would vary with different bullet weights, powders, BC etc... theres so many other variables though.
In theory it can be done, but playing with the powders to try to get the same velocities could create excessive pressures in the barrel if not done carefully in my view. this because you are trying to create the same acceleration in the barrel as with a longer barrel. It may even kick more due to the higher acceleration
I think if you chop down a barrel then you have to live with the difference and adjust to the new trajectories that comes with a shorter barrel.
 
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