Muzzle velocity
- Thread starter kodiak
- Start date
Is there a rule of thumb regarding the change in muzzle
Art Eatman
Staff in Memoriam
About every ten years or so, somebody goes to chopping barrels and chronographing the result.
As near as I can tell, cartridges of the .220 Swift, the .30-'06 sort and the bigger magnums do a bit worse than such as the .308 or .243.
I'd go along with the 25 ft/sec per inch of barrel cut back from the used-to-be "standardmeasurement" of 26 inches, for the .243/.308, etc. For the '06 and others, it's around 50 ft/sec and in a few cases up to 70 ft/sec per inch.
FWIW,
Art
"One chronograph test beats a thousand expert opinions."
As near as I can tell, cartridges of the .220 Swift, the .30-'06 sort and the bigger magnums do a bit worse than such as the .308 or .243.
I'd go along with the 25 ft/sec per inch of barrel cut back from the used-to-be "standardmeasurement" of 26 inches, for the .243/.308, etc. For the '06 and others, it's around 50 ft/sec and in a few cases up to 70 ft/sec per inch.
FWIW,
Art
"One chronograph test beats a thousand expert opinions."
I couldn't tell you what kinda calibers do what when you cut em. But I can tell you that I know four guys including myself who have cut there mod 70 .375's from 24 to 20 inches and as far as I can tell haven't lost a darn thing in muzzle velocity. I'm pushing 285gr grand slams at just over 2700 fps with factory Nitrex loads. Same as it was with a 24 inch tube. I don't think it has much affect on .308's or 06's either. I'd be interested to see what it does to something like a .300 win or weatherby mag. A few years ago I cut a 26'' .338 win mag to 20 inches. That didn't work out to well. I never chronographed it but the thing was blowing unburned and fizziling powder out the muzzle. Oh well live and learn.
Barrel length
One thing seems kinda obvious if you think about it....if you have a lot of powder to burn it usually takes a longer barrel. A Weatherby with a 16" barrel would be kinda silly. There was a pretty extensive article in Handloader a few issues back.
If you look in the revolver forum there's a link to an article in Sixgunner about the 45LC in pistols and rifles. Seems like the little old Colt 45 is pretty impressive with some of the handloads (260 grain bullets at 1750 fps).
One thing seems kinda obvious if you think about it....if you have a lot of powder to burn it usually takes a longer barrel. A Weatherby with a 16" barrel would be kinda silly. There was a pretty extensive article in Handloader a few issues back.
If you look in the revolver forum there's a link to an article in Sixgunner about the 45LC in pistols and rifles. Seems like the little old Colt 45 is pretty impressive with some of the handloads (260 grain bullets at 1750 fps).
According to tests Tactical Operations performed (BARREL LENGTH AND THE PRECISION RIFLE, Why shorter barrels may often be better by Eugene Nielsen, SWAT Magazine, Dec. 2000):
"During the development of the Tango 51, Tac Ops took a standard 26-inch barrel and cut it down to 18 inches in one-inch increments. Between 10 to 20 rounds were fired at each invrement. They found that a 20-inch barrel provides for a complete propellant burn and no velocity loss when using Federal Match 168-grain BTHP, a cartridge that has become something of a law enforcement standard. Going to an 18-inch barrel only resulted in a loss of 32 feet per second (fps)."
"According to Tac Ops, there isn't any need to go to the 26-inch barrel unless you want to go to a heavier bullet or push the round to higher velocity using more powder or use a slower burning powder."
"Tac Ops took a 26-inch barreled .300 Win. Mag. and chopped the barrel down in one-inch increments as they previously did with the .308 Winchester. Ten rounds of Federal Match 190-grain BTHP Gold Medal were fired from each increment. No velocity was lost from 26 inches to 22 inches. Velocity loss started to occur only after they went below 22 inches"
"As a result of their tests, Tac Ops decided not to go below 22 inches on their .300 Win. Mag. tactical precision rifle, the Alpha 66. According to Mike Rescigno, President of Tac Ops, the 22-inch barrel is ideal for the tactical shooters that are going to use the 190-grain Federal Match ammo. There isn't any loss of performance by going to the 22-inch barrel and this round. The Alpha 66 still provides 1/4-MOA or better accuracy."
A copy of this article can be viewed on their website, www.tacticaloperations.com.
Very interesting....Anyone have any other info that would support this?
"During the development of the Tango 51, Tac Ops took a standard 26-inch barrel and cut it down to 18 inches in one-inch increments. Between 10 to 20 rounds were fired at each invrement. They found that a 20-inch barrel provides for a complete propellant burn and no velocity loss when using Federal Match 168-grain BTHP, a cartridge that has become something of a law enforcement standard. Going to an 18-inch barrel only resulted in a loss of 32 feet per second (fps)."
"According to Tac Ops, there isn't any need to go to the 26-inch barrel unless you want to go to a heavier bullet or push the round to higher velocity using more powder or use a slower burning powder."
"Tac Ops took a 26-inch barreled .300 Win. Mag. and chopped the barrel down in one-inch increments as they previously did with the .308 Winchester. Ten rounds of Federal Match 190-grain BTHP Gold Medal were fired from each increment. No velocity was lost from 26 inches to 22 inches. Velocity loss started to occur only after they went below 22 inches"
"As a result of their tests, Tac Ops decided not to go below 22 inches on their .300 Win. Mag. tactical precision rifle, the Alpha 66. According to Mike Rescigno, President of Tac Ops, the 22-inch barrel is ideal for the tactical shooters that are going to use the 190-grain Federal Match ammo. There isn't any loss of performance by going to the 22-inch barrel and this round. The Alpha 66 still provides 1/4-MOA or better accuracy."
A copy of this article can be viewed on their website, www.tacticaloperations.com.
Very interesting....Anyone have any other info that would support this?
With all due respect to redneck2 the amount of powder in the case doesn't seem to be all that realative to barrel length vs velocity. Case in point is my example of the .375. That case holds quite abit of powder wouldn't you say? In fact looking at the last Barnes manual a .375 has a case capacity of 96.37 grains of water vs a .300 weatherby's 100.36. I beleive that it has a lot more to due with peak pressure curve rate in the barrel it self. The old theory of longer barrel equals more velocity and accuarcy stems from low pressure black powder rifles that needed a longer barrel for sight radius & accuarcy. Obvously there is a point of diminshing returns on all calibers as far as lentgh goes in both directions the example of a 16 inch weatherby is entirely correct however it may also be a fact that a 26 inch tube on the same gun has 4 inches of wasted barrel. That extra four inches can be a hassel when manuvering in and out of a tight space like the back seat of an airplane.
Barrel length and velocity are related
by what is called "Expantion Ratio".
The volume of the chamber and interior of the barrel compared to the volume of the chamber is the Expantion Ratio. The bigger the ratio, the more velocity (all else being equal). It is also why cutting off a 22lr barrel looses less velocity than cutting off a 300 Weatherby.
See if you can find an online version of the "Powley Computer". It really explains the concept in a graphic manner.
by what is called "Expantion Ratio".
The volume of the chamber and interior of the barrel compared to the volume of the chamber is the Expantion Ratio. The bigger the ratio, the more velocity (all else being equal). It is also why cutting off a 22lr barrel looses less velocity than cutting off a 300 Weatherby.
See if you can find an online version of the "Powley Computer". It really explains the concept in a graphic manner.