Velocity loss from shortening a barrel

[bat119]

A question that comes up regularly is how much velocity is lost by barrel length.
I bought a Browning stalker in .338 with a 26" barrel, I decided to shorten to 21" add a Vais brake. Before sending it off to get shortened I made up a medium load with a 225 gr. bullet @ 2635 fps after knocking off 5" of barrel and adding the brake the same load was 2580 fps. the loss was only 55 fps. Maybe because it was a low pressure load?

[elkhunter11]

Were the temperatures the same for the chronographing before and after?

[bat119]

Yes it was about -10 both times I shot 2 3 shot strings both tests

[elkhunter11]

Which chronograph are you using? I have the Chrony units, and they usually don't like to work below 0. I have resorted to placing chemical hand warmers around the electronics.

[Cappy]

Depending on case capacity and burn rate of the powder used. Velocity loss can be more significant or less significant based on the those variables.

If are using a slow powder to drive a light for caliber bullet you generally need a longer barrel. If you use a faster powder for a heavier bullet then the pressure is reached much quicker and a longer barrel, while still making a difference isn't as significant. (obviously these are generalities and lots of variables can come into play)

Just chopped a .308 barrel all the way down to 16" and with factory match ammo from Lapua I'm still getting 2561fps compared to the 2650fps I had in the 20" barrel before.

Chrono used was a Magnetospeed, not light or temp sensitive like mentioned above.

Bottom line is you never know until you do it.

[bat119]

My load was 70 gr. SC H 4831 225 Hornady bullet
Never me or my chorny was outside long enough to reach ambient temp.the range wasn't busy either
The load was 5 gr. under max I'll do some testing in the spring

[Northwinds]

I cut a .358 Norma back from 26" to 20',lost 21fps per inch. The big bores do not lose much velocity with a chop job as bad as .284 and under.

[gitrdun]

Some of that may also depend on which powder you're burning.

[gitrdun]

Some of that may also depend on which powder you're burning. Fast burning = less, Slow burning = more. Theoretically.

[RatFink]

Originally Posted by Cappy

Depending on case capacity and burn rate of the powder used. Velocity loss can be more significant or less significant based on the those variables.

If are using a slow powder to drive a light for caliber bullet you generally need a longer barrel. If you use a faster powder for a heavier bullet then the pressure is reached much quicker and a longer barrel, while still making a difference isn't as significant. (obviously these are generalities and lots of variables can come into play)

Just chopped a .308 barrel all the way down to 16" and with factory match ammo from Lapua I'm still getting 2561fps compared to the 2650fps I had in the 20" barrel before.

Chrono used was a Magnetospeed, not light or temp sensitive like mentioned above.

Bottom line is you never know until you do it.

That's quite an acceptable velocity loss. I once read that .308s lose 50fps/1" loss on a barrel.

[Cappy]

.308 is a relatively small case and most of the powder gets burned pretty quick. I was pretty shocked at how little velocity was lost and was expecting to be down around 2500 even.

[DaleJ]

Some combinations of fast twist long barrels benefit velocity-wise by shortening. The M96 Swedes with their original 29" 1:7 (?) barrels would gain velocity by shortening to 24".
If a custom build is in the works a fast twist shorter barrel may produce better velocity than a long slow twist barrel, by lengthening high pressure span. Burning powder produces pressure proportional to its temperature and pressure.
I have a few RKS gain twist barrels. The short ones produce better velocity than the long barrels. I had a 30" 18-9:1 7mm RKS chambered 7 Rem Mag that would not get 2800 fps with 168 gr bullets. Have a 22" RKS 16-8:1 chambered 7 WSM that easily does 3000 fps with 168 gr. Not scientific but interesting.

Just another angle on barrel length and velocity