20" barrel vs. 18 1/2" barrel 00 buck spread (or any size shot)


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F1ST0
April 25, 2013, 01:01 AM
Between 20 inch barrels and 18 inch barrels, is there a dramatic difference in spread patterns?

Thanks.

EDIT:
Sorry if this question has already been asked, but I've searched for it already and found nothing, so I figured I'd ask.

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X-Rap
April 25, 2013, 01:42 AM
It will depend on the choke more than anything else. If both barrels are just cut off and have open chokes I doubt the 2" will make any difference either.
These are just generalizations and you won't know for sure until you pattern the guns since there can be some variation even with the same choke.

Inebriated
April 25, 2013, 02:30 AM
The 20" will have slightly more velocity, but pattern is never really affected by barrel length. Not in my experience, anyway.

bikerdoc
April 25, 2013, 07:42 AM
My Mossberg 500 with 20 inch barrel and modified choke gives me a good Pattern at 30 feet and since it is my HD gun I am confident it will do the job.

YMMV

Fred Fuller
April 25, 2013, 10:35 AM
I've never seen where 1.5" of barrel (factory barrels that is) either way makes any real difference in either velocity or pattern.

waterhouse
April 25, 2013, 10:42 AM
I own benelli barrels in 18.5, 21, and 24". At 25 yards and choked the same you would have to take a ruler to figure the difference in buckshot group size.

It probably also depends on the load; the federal flite control stuff can generally be covered with my fist from any of the 3 barrel lengths.

LeonCarr
April 25, 2013, 11:28 AM
No real difference

Just my .02,
LeonCarr

Sheepdog1968
April 25, 2013, 12:13 PM
All other things being equal where barrel length is the only difference, you won't notice any difference.

F1ST0
April 25, 2013, 03:27 PM
I forgot to mention the choke is open cylinder improved cylinder.

Texan Scott
April 25, 2013, 04:32 PM
No.

oneounceload
April 25, 2013, 04:40 PM
Barrel length has ZERO value regarding pattern
Those barrel lengths will be the same velocity - shotguns tend to max out right about 18 inches

F1ST0
April 25, 2013, 05:23 PM
Thanks for the help, everyone, I guess the only reason to have a 20" barrel is to hold more rounds.

Zoogster
April 25, 2013, 06:50 PM
And sound, every inch in a shotgun significantly reduces report.

The difference between an 18" and a 26" barrel for example is great.
The large bore means each inch of length results in a lot more space for compressed gas to expand into which reduces the pressure it finaly escapes the muzzle at.
A single inch of .729 bore gives 1.67 additional cubic inches of space.
Compare that to a ~.30 inch rifle bore that would need almost 6" inches of barrel to create that much space.
This means an additional 2 inches of unchoked 12 gauge bore is giving as much additional internal space for gas to expand into as nearly a foot of a .30 caliber rifle barrel.
Or lets compare to popular .223/5.56 (actual bore is around .224), where it would take about 10.6 inches of barrel to give the internal space of a single inch of 12 gauge. And an additional 2 inches of 12 gauge barrel is giving over 21 inches of .223 rifle bore space.

And the difference of the 8" of bore space between an 18" and a 26" barrel would be 13.36 cubic inches the amount of space in over 84" of .223/5.56 barrel. So it has as much extra internal space as an extra 7 feet of .223 barrel.
The whole 26" barrel would have around 43.43 cubic inches. Or as much internal space as 275" or nearly 23 feet of .224 barrel.

Which starts to seem a lot more signficant in those terms, and you can see why just a few inches in 12 gauge makes such a difference in reducing the volume of the report.

Being relatively fast burning and operating at low maximum pressure with a large bore volume most shotgun powders have completely burned before getting anywhere near the muzzle. So that additional volume for gas to expand continues to drop pressure and report volume.
Decibels are in a logarithmic scale, so the difference between 150 and 160 decibels for example is a lot more than the seemingly minor numerical difference of 10.

This can mean the difference of being nearly deaf for awhile after firing indoors and simply having reduced hearing.
That doesn't mean increased length outweighs how handy and convenient a shorter barrel is maneuvering in confined spaces, only that it was an unmentioned benefit of a longer barrel when weighing pros and cons.

lemaymiami
April 26, 2013, 10:00 AM
Both Mr. Fred, and oneounce have it right. Whichever you choose -make a point of patterning it out with standard buck rounds and make sure you do it from the 3, 7, 15, and 20 meter distances... I'd expect exactly seven inches spread at 7meters - that's what every police shotgun we checked (they varied from Mossberg to Remington, 18 to 20" barrels...) gave us. Knowing what the spread will be at given distances will make you a much more skilled operator if that weapon is ever needed....

If you choose to get away from standard 2 3/4 rounds to something more powerful or with claims of tigher patterning then you'll need to do those patterning routines again to find out how they actually perform...

Deltaboy
April 26, 2013, 10:41 AM
The shorter barrel is just more maneuverable inside a home.

natman
April 26, 2013, 01:43 PM
Between 20 inch barrels and 18 inch barrels, is there a dramatic difference in spread patterns?


No.

Pete D.
April 27, 2013, 08:08 AM
I'd expect exactly seven inches spread at 7meters - that's what every police shotgun we checked (they varied from Mossberg to Remington, 18 to 20" barrels...) gave us. Knowing what the spread will be at given distances will make you a much more skilled operator if that weapon is ever needed....
How were those choked? I ask because a standard reference for shot spread has been one inch per yard for a FC'd gun and two inches per for CYL.
That is from the NRA Firearms Fact book......I wonder, though, whether the NRA data is accurate in this day and age.
Pete

lemaymiami
April 27, 2013, 08:05 PM
From memory all of the weapons we checked were standard issue 12ga. marked "improved cylinder". These were items that had seen and would continue to see hard service - not necessarily in shots fired but in all the bad things that can happen to weapons in electro-locked daily carry positions in one squad car or other. We were trying to get the point across to a wide range of officers that you had to be aiming with those poppers if you wanted to be hitting... I took those lessons to heart and they made be a very confident 'gunner in high stress situations. On the street, confidence backed up with skill is the only way to operate.

F1ST0
April 28, 2013, 02:41 AM
Zoogster, thanks for that extra info, very awesome that you know that, I had no clue that noise report was in the equation.

Thanks, guys.

F1ST0
April 28, 2013, 02:43 AM
Deltaboy, I asked this because I wanted a rifle sighted (and upgraded to trijicons) 20" barrel for a SHTF/survival shotgun, not HD. I have a bead-sighted 18.5" barrel on my 870 right now, and I feel a bead sight wouldn't be adequate for slug shooting at longer distances, and my shotgun is the only weapon I have right now.

But I've recently been looking into an EOtech for my shotgun.

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