12ga muzzle velocity? Barrel length.

Deja vu · March 25, 2014, 11:24 PM

I am wondering if there is a chart some where of muzzle velocity of shot relating to barrel length? How short can a barrel be before you start loosing significant velocity? I have shot a police SBS that was an 870 with a 12 inch barrel and the velocity was very comparable to my 18.5 and 26 inch barrel guns only loosing about 50-70 FPS depending on the round fired.

p.s. purely for academic reasons. Though I may make a NFA SBS some day.

Virginian · March 26, 2014, 05:44 AM

Depends on the load, powder and shot weight make some difference. The general consensus is that you will lose some velocity, maybe 20 to 50 fps for every inch from about 30" on back. And for all the people who will say the powder is burned in the first 18" or so of barrel, that may be true but the gasses generated by the powder are still behind the shot and still pushing. I did some checking years ago with heavy loads in the 26" to 30" range and it verified that. The rate of loss per inch may change when you get a lot shorter, I don't know.

jmr40 · March 26, 2014, 10:45 AM

There has been much more research done with rifles. VERY VERY few rifles lose more than about 15-25 fps/inch when cut shorter. The most I've ever seen documented was 35 fps when a 300 mag barrel was cut. Shotguns as a rule lose even less, and shot speed is less important than bullet speed to perfromance. I'd say that as long as it is the legal length the loss compared to a typical 26-28" barrel won't be enough to matter.

The confusion comes when people start comparing gun "A" with a certain barrel length to gun "B" with a shorter length. The numbers can be all over the place when you make those comparisons. You can have 100 fps difference between 2 individual barrels of equal length. Sometimes a 2" shorter barrel will be 150 fps slower, sometimes 50 fps faster. The only relevant numbers are those you see where someone tested this using the same barrel and cutting it shorter and testing as they progressed. When you look at those numbers the velocity loss is far less than commonly thought.

olddrum1 · April 4, 2014, 03:36 AM

For most store bought shells, that is true, but in reloading there are powders that will still have powder burning at 26 to 30 inches. Winchester 571 and Hodgdons 7 are two of these. Also on these slower powders extreme cold weather (where the shell actually gets cold) will effect the speed of these shells also. Just repeating what VIL posted.

Virginian · April 4, 2014, 05:28 AM

You can add Blue Dot to that list, too olddrum1. I burned a lot of 571, Blue Dot, and 4756 before the curtain finally fell on lead shot.

March 25, 2014, 11:24 PM	#1
Deja vu Senior Member Join Date: March 14, 2010 Location: Border of Idaho & Montana Posts: 2,584	12ga muzzle velocity? Barrel length. I am wondering if there is a chart some where of muzzle velocity of shot relating to barrel length? How short can a barrel be before you start loosing significant velocity? I have shot a police SBS that was an 870 with a 12 inch barrel and the velocity was very comparable to my 18.5 and 26 inch barrel guns only loosing about 50-70 FPS depending on the round fired. p.s. purely for academic reasons. Though I may make a NFA SBS some day. __________________ Shot placement is everything! I would rather take a round of 50BMG to the foot than a 22short to the base of the skull. all 26 of my guns are 45/70 govt, 357 mag, 22 or 12 ga... I believe in keeping it simple. Wish my wife did as well...

March 26, 2014, 05:44 AM	#2
Virginian Senior Member Join Date: February 11, 2012 Location: Williamsburg, Va. Posts: 1,528	Depends on the load, powder and shot weight make some difference. The general consensus is that you will lose some velocity, maybe 20 to 50 fps for every inch from about 30" on back. And for all the people who will say the powder is burned in the first 18" or so of barrel, that may be true but the gasses generated by the powder are still behind the shot and still pushing. I did some checking years ago with heavy loads in the 26" to 30" range and it verified that. The rate of loss per inch may change when you get a lot shorter, I don't know. __________________ What could have happened... did.

April 4, 2014, 05:28 AM	#5
Virginian Senior Member Join Date: February 11, 2012 Location: Williamsburg, Va. Posts: 1,528	You can add Blue Dot to that list, too olddrum1. I burned a lot of 571, Blue Dot, and 4756 before the curtain finally fell on lead shot. __________________ What could have happened... did.

March 26, 2014, 10:45 AM	#3
jmr40 Senior Member Join Date: June 15, 2008 Location: Georgia Posts: 10,805	There has been much more research done with rifles. VERY VERY few rifles lose more than about 15-25 fps/inch when cut shorter. The most I've ever seen documented was 35 fps when a 300 mag barrel was cut. Shotguns as a rule lose even less, and shot speed is less important than bullet speed to perfromance. I'd say that as long as it is the legal length the loss compared to a typical 26-28" barrel won't be enough to matter. The confusion comes when people start comparing gun "A" with a certain barrel length to gun "B" with a shorter length. The numbers can be all over the place when you make those comparisons. You can have 100 fps difference between 2 individual barrels of equal length. Sometimes a 2" shorter barrel will be 150 fps slower, sometimes 50 fps faster. The only relevant numbers are those you see where someone tested this using the same barrel and cutting it shorter and testing as they progressed. When you look at those numbers the velocity loss is far less than commonly thought.

April 4, 2014, 03:36 AM	#4
olddrum1 Senior Member Join Date: March 23, 2008 Location: Mid Missouri Posts: 807	For most store bought shells, that is true, but in reloading there are powders that will still have powder burning at 26 to 30 inches. Winchester 571 and Hodgdons 7 are two of these. Also on these slower powders extreme cold weather (where the shell actually gets cold) will effect the speed of these shells also. Just repeating what VIL posted.