Barrel length & speed

GoatHerder

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Jul 23, 2017
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How much bullet speed is gained or lost per inch of barrel? Also is the gain or loss equal? Example if it were 50 ft./s per inch of barrel would you lose 50 feet with an inch shorter barrel and would you gain 50 feet with an inch longer barrel?
 

Mikecr

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Loss/gain here is not fully linear.
Once barrel length drops below some point loss rate increases, and once beyond some point gain rate decreases
Blength.jpg
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A mid point would be an abstract summation of all load attributes.
 

MagnumManiac

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Feb 25, 2008
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In some cartridges as little as 20fps is lost with 2” less barrel.
There really is no set amount per inch gained or lost as Mikecr said.

Cheers.
 

Mikecr

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There is more to choosing barrel length than muzzle velocity, as there are prices for everything.
There are powder nodes, and barrel nodes, which are different things -combining to result.
Barrel nodes favor shorter/stiff barrels.
Powder nodes favor barrels long enough to well burn the powder.
You might reach for best balance.

A 6.5x284 pushes heavy for cal bullets using a lot of slow burning powder. With a long barrel, let's say 30", a little variance in powder burn has barrel time to normalize. If the barrel is short, say 24", variances in powder burn will likely plague results. You're also producing way different muzzle pressures here, which can affect quality of bullet release.
That's not to suggest short barreled 6.5x284s won't be accurate, but I wonder how forgiving this would be.
How reliable will the cold bore single shot accuracy be?
Considering his, I would go at least 28", ~heavy palma contour.

For a 260AI capacity with 140gr bullets, 28" has been as perfect as QuickLoad predicts.
For a 6.5x47L with 130gr bullets, I would go 26" barrel.
'Perfect' for me is the fastest powder that fills the case, producing SAAMI max, with muzzle pressure <8kpsi.
This standard has led me nearly directly to best loads in 22, 24, and 26cal.
 

WItoOR6637

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Dec 26, 2020
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so by this example a 160 grn @ 2950 out of a 280AI 24" would only loose 50-70fps by cutting down to 22"?
 

longestrange

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Dec 26, 2013
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The GSC website has published load data for their SP VLD bullets that includes both % burn and fps/in along with %case fill. Their bullets can be loaded faster than regular bullets due to the drive-band technology so beware! In the individual bullet description tables they have min/max seating depth, barrel twist rate vs. stability, G1/G7 BC's etc. For a 24" class bbl they list most 26 cal loads as around 25 fps/in. My experience has been that you can get more velocity at equivalent pressures with these bullets.
 
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