Velocity vs. Barrel length


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ssyoumans
April 21, 2011, 01:24 PM
So, with pistols and rifles it is easy to chrono and see what your velocity is out of different length barrels. What about with shotguns?

For slugs, 00 buckshot and #4,5,6 turkey loads, what is the velocity loss going from a 28" barrel to a 18" barrel? I wish the site, ballistics by the inch tested shotguns.

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jmr40
April 21, 2011, 02:15 PM
In a nutshell the longer barrels on a shotgun will shot faster than shorter barrels just like in rifles and handguns. The difference however will be far less noticeable with shotguns than rifles.

Some folks get all worked up over 2-4" when the difference is hardly noticeable in the field. I don't have any references, or experience chronographing shotgun loads, (rifle yes) but 10" might make a little difference.

Dave McCracken
April 21, 2011, 02:42 PM
The Tech Staff at the NRA a few decades ago took a Marlin Bolt action Goose Gun with a 36" barrel, chronographed it with varied loads and started cutting it in one onch increments. Barrel was cut square and recrowned each time.

IIRC, highest velocities occurred around 24-26". Lowest velocity at the extremes. They stopped at 18".

RaceM
April 21, 2011, 02:51 PM
I did some web research on this very subject. Found an article stating that most of the acceleration of the shot occurs in the first 12-14" of the tube, then the rate of acceleration gain drops (not stops) as the tube gets longer out to 28-30". The main thrust of the article was the effect of lopping several inches off a long tube to make it suitable for home defense purposes. If I recall correctly the drop in velocity cutting a 24" tube back to 18 was only a couple hundred fps. All I can say for definite is that when I cut my 835 Mossy from 28" to 20" it still thumps you hard with heavy loads and the down-range results (as far as impact energy) remain impressive.

smurfman
April 21, 2011, 08:12 PM
In a 12 ga you will lose or gain approximately 5 feet per second in velocity for every 1" change in barrel length when using shot and 7.5 fps for slugs. So, you can expect a change of about 50 fps to 75 fps when cutting back a barrel 10". This is per many different sources, the one I checked with last was Lyman's Shotshell Reloading Manual. That same velocity difference is what one can expect from the extremes in a box of Gold Medal, AA, or STS target loads, you know the ones with the the best quality control, so I would not let it bother me at all.

kozak6
April 21, 2011, 09:13 PM
It doesn't really make a big difference into you are well into NFA territory.

oneounceload
April 21, 2011, 09:54 PM
the difference between 18 and 24 is basically nothing. The difference between 24 and 28 is basically non-existent......

there is not enough difference (unlike pistol or rifle) to be concerned about

Virginian
April 21, 2011, 10:03 PM
Rule of thumb is around 25 fps loss per inch, but powder and payload will have some effect.

oneounceload
April 21, 2011, 10:09 PM
I'll disagree when it comes to shotguns - there ARE losses in metallic, the differences in shotguns is minimal at best and for all intensive purposes, not worth worrying a bout

jmr40
April 21, 2011, 11:11 PM
It would be pretty rare for a rifle to lose 25 fps/inch in velocity. Wouldn't think a shotgun would be anywhere near that. Someone else mentioned 5fps/inch. That seems much more reasonable for a shotgun.

matrem
April 21, 2011, 11:40 PM
Considering the fact that shotgun loads use the same or similar burn rate powder that we load in our 3"- 6" handguns, those inches of bbl length can "run out of steam" rather quickly.

robhof
April 21, 2011, 11:42 PM
The longer barrels aren't for higher velocity, but for tighter relative groups, an 18" with full choke will have a considerably larger group than a 30" at distances greater than 20 yds.

oneounceload
April 22, 2011, 09:56 AM
The longer barrels aren't for higher velocity, but for tighter relative groups, an 18" with full choke will have a considerably larger group than a 30" at distances greater than 20 yds

HUH? Not exactly...........two identical guns, one with a full choke 18" barrel and one with a full choke 30" barrel will have the same pattern density. The choke constriction determines that, not the barrel length. Where the longer barrel has the advantage is on swing dynamics against moving targets - it allows for a steady smooth swing, not a herky-jerky swing that stops too easily resulting in a miss

jmr40
April 22, 2011, 12:17 PM
The longer barrels aren't for higher velocity, but for tighter relative groups, an 18" with full choke will have a considerably larger group than a 30" at distances greater than 20 yds.

Don't tell all my 20" turkey barrels that. With the tighter choke tubes they shoot just as tight as any longer barrel

Virginian
April 22, 2011, 05:02 PM
From my high powered rifle days I seem to recall that relatively high velocity rifles lose a lot more than 25 fps per inch.

jmr40
April 22, 2011, 06:42 PM
If you get into magnum rounds with extremely short barrels that would be the case. With 308 and 30-06 class rounds in barrels longer than 20" I've never lost more than 25fps/inch. Mostly 10-20fps /inch diffference.

There is lots of data out there, but some myths just refuse to die.

Virginian
April 23, 2011, 02:16 PM
Well, y'all made me look, but i can't find my stuff. But, I remember the difference with the same 25-06 117gr. boattail spitzer loads over 4350 powder was 132 chronographed feet per second slower out of a 22" barrel versus a 24", and with a 280 Remington/7mm Express the difference was 110 fps, and i think that was 4064 powder. That's no myth. I can't remember the other stuff. Shotguns are relatively low velocity, so I would expect the difference to be less.

jmr40
April 23, 2011, 06:59 PM
Comparing the velocity of 1 gun vs another gun is useless. I have no doubt of your numbers, but I've gotten 100fps faster with 2 guns with equal barrel lengths with ammo out of the same box. Did it consistently with several factory and handloads. I have a 20" 308 that consistently shoots 10-20 fps faster than any of my 22" 308's with every load I've tried.

The only standard that proves anything is chronographing ammo from a longer barreled rifle, then chronographing the same ammo through the same gun after the barrel has been shortened. This has been tried dozens of times and there are many reports of the results available. I've also corresponded with several guys who have shortened their barrels for various reasons.

If you dip below 20" or so you start seeing bigger drops in velocity. The longer you go the smaller gains you see. Of all the test reports I've read, and based on my personal experience it is rare, but possible, to see more than a 25fps loss in velocity per inch. You will almost always see at least that much difference between different guns with equal barrel lengths. The largest loss of velocity I can find documentation for is around 35 fps/inch from a 300 mag that was cut down to 20". There is a very good reason why almost all hunting rifles have barrels between 20"-24".

Somehow the word got out that you could expect to lose 50 fps/inch. I've never found any proof of that when you use the same barrel. Not even close.

Remo223
April 23, 2011, 07:32 PM
Seems to me the really long barrels (more than 30") really do have an effect on power for 10ga shotguns. Ten gauge has a bigger powder charge but operates at lower pressure than 12ga. The extra long barrels are even more important with the older black powder ten gauge guns.

They didn't make 36" goose guns a hundred years ago for nuthin. They knew what they were doing.

berettashotgun
April 23, 2011, 08:04 PM
A loose crimp on a shotshell has a tremendous affect on pressure; having put a few payloads into everything that flies with a .410 thru a 10ga, I'd guess the 20" - 26" barrel is good for what you need.
A 18" shotgun barrel will suffice plenty well for social work, MUCH better than a whack with a stack of "ballistic" charts showing the most-est powerful/highest velocity loadings.
I have used a 32" barrel for my swing control and went crazy with a bore gauge to get the perfect choke for a Beretta 303 and 390. I had a better pattern with a factory full than any aftermarket choke.

oneounceload
April 24, 2011, 09:28 AM
Comparing velocity losses from rifles to shotguns is superfluous - shotguns run around 8-10,000 psi, rifles are up in the 50K range

As mentioned above, a bad crimp will do more to shed velocity than a short barrel

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