20" barrel length inefficient?

[tt600]

I was reading several forums about barrel length vs. velocity.

I saw this

http://www.thehighroad.org/showthread.php?t=360565

and this

http://forum.saiga-12.com/index.php?showtopic=19103

Basically the data showed that 20" barrels got slower velocities than either
18" or 28". Now that I just bought a shotgun with a 20" barrel I am a little worried. How could the 20" length be "bad"? Seems like the data should not have a trough at 20". Is this just not enough data or is something weird going on at 20 inches? I can see velocities rising up to a certain length, say 30" and then falling but to have a dip right at 20" does not seem logical.

 

[Youngster]

There could be something to it, I've seen other tests where they was also a "dip" at 20". As to why, who knows, maybe some kind of turbulence or gas flow reversion dynamic kicks in at that point in a 12 gauge barrel?

There's just so much about ballistics, whether its internal, external or terminal, that seems counterintuitive.

 

[LaserSpot]

That chart also shows dips in velocity at 18", 23", 25", and 27". There's no way that the shot charge could slow down at 20", then speed back up; these are just random variations in the ammo.

 

[natman]

There is no way the shot could slow down and then speed up again. It's just experimental error.

Shotguns only gain a little velocity with longer barrels. Switching from a 22 to a 28 gets you about 50 fps for the entire 6" difference.

http://www.guncustomizing.com/tech.htm#barrelvelocity

 

[tt600]

I looked the net for more info. I would agree that any test should have lots of shots per length to even out the data. If there was still a dip at 20" then something weird could be going on. What that could be mystifies me. Just looking to see what possibilities people could think of. The only thing I could think of is that as the shot charge moves down the 20" barrel there is some resonance that creates extra air pressure ahead of the charge.
I looked at the above mentioned chart but it only goes from 22"-28". Any other charts on the net with more lengths?


I suppose I could just get some extended choke tubes.

 

[AcceptableUserName]

given that you have a 20" barrel, I'm assuming it's with a defensive purpose in mind...


my question is, would the target ever know the difference?

 

[oneounceload]

Any minimal loss in velocity would not be noticed by whatever you hit

 

[tt600]

I got it for many purposes (outback) but hopefully it will shoot a lot more birds and rabbits than people. I have to admit that a 20" barrel makes it somewhat challenging to hit wingshots.

 

[MachIVshooter]

Ammo variations.

Though minimally, the velocity will continue to increase to 30" and farther. That said, shot loads achieve complete powder burn well short of even 18". Velocity gains diminish as the tube gets longer, but they're not gonna slow down, unless that barrel is rediculously long.

 

[ElToro]

depending on choke, the only differnce between 20 and 28 for animals or clays is the shot starts 8 inches closer and how the weapon balances/swings for you. if your 20 incher is too open ( probly open cylinder) look into getting it choke threaded by briley or similar. some short barrels do have screw in chokes though i think benelli may be one i can't recall seeing an 870 with 20 incher being adjustable choked at the factory. i dont shoot trap often but i have done it with an 18 inch 870 and hit 18-20 of 25 with an open cylinder bore gun as well as a really cut down A5 that is probly more than open cylinder . once you know where your shot is going you can make adjustments at minute of living room range its not going to make a difference

 

[inSight-NEO]

I guess the term "inefficient" only applies based on ones needs. I keep a 20" barrel (Mossberg 590A1) shotgun around for various needs and have no complaints thus far, based on my experience with this gun.

Having said this, I tend to think of 18" to 20" barrels as being more for "general use" and "HD" vs. hunting duty.

But, I know what you mean. I too have read the "research" regarding the anomaly of the 20" barrel. But, even with the supposed drop in velocity, I do not think it is substantial enough to be the difference between a kill vs. no kill. Just my .02 cents.

 

[RMc]

Short barrels

and heavy loads may have problems: If a 3 or 3.5 inch magnum is fired in a short barrel - depending on the load - the pattern may be disrupted by excessive gas pressure at the muzzle. The best patterns call for minimal muzzle pressure.

 

[oneounceload]

Shotgun shells typically have peak pressure somewhere around 14" in the barrel - the main disadvantage of a short barrel is the swing dynamics really suck

 

[Bud Tugly]

Unless you were shooting at extreme long ranges, I doubt if you or your target would ever notice any difference.

 

[MutinousDoug]

A longer shotgun barrel gives you a better swing and sightplane than terminal performance improvement.