How short to get 13” pattern at 30’?

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becket

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I want a sbs for the house with a 12” pattern from a 12 ga., at 20 feet. Open cylinder.
What length barrel would I need to stamp? Would I get more burn from a 20 gauge in that length barrel?
High brass, oo to 0000 buck?
Thanks
 
Barrel length doesn't have any effect on pattern. The choke determines the pattern you get. 18" is the legal minimum barrel for a shotgun with 26" minimum overall length. That means most doubles will need to have barrels longer than 18" to meet the 26" overall requirement. The Mossberg shockwave and similar guns fall into a loophole in the law. They are not considered shotguns and have their own rules. I don't recommend those type of guns, but that is another thread.

With a cylinder bore around 1" per foot is the number I've seen thrown around, but I've never tested the theory. If true expect 20" patterns at 20'. Something with interchangeable choke tubes and an Improved Cylinder choke should tighten up patterns. Remington makes an 870 intended for turkey hunting with a 21" barrel that takes choke tubes and is what I have on my HD shotgun.

All of the powder is burned in the 1st few inches in all shotguns. Longer barrels give the pressure generated by the powder more time to accelerate the projectiles and will increase velocity. But there is very little to be gained with shotgun barrels over 18". Stay with a 12.
 
Roger that thanks. I am experienced with sporting shotguns and had a shockwave. I reload for Skeet but did not know the burn rate in very short barrels of the older powders we are stocked up on. Thanks for the tip on that; saves me hunting down my old Jethro Bodine powder cypherin’ chart books! I want a sbs (short barrel shotgun) that I plan to pay my $200 stamp for. I know that in an open cylinder with a thin wad, a cut down 15” 12-ga barreled coach gun will open up ‘some’ at 20’ (the length of my longest room) but I don’t own one just yet; and won’t just hack away at a longer barrel. I need a shortie with a short-isg stock I can move around quickly. I dunno if there are any ready made autos or pumps that will allow a much shorter than 18” barrel that have short enough actions? Yes I can always fall back on a short double; rather have 4+ though. It’s for a space by my couch (zero kids here!) between my bedroom and living room. If I get a sudden door kicker or other surprise intruder, my wife or I can (on paper at least) deliver a quick and LOUD attack, to give us an extra second or two of time to get to my high-caps. In answer to the next question: because I only have one AR; and its not for that room.
My wife can handle a shottie well enough, but I want that spread for her or I to maybe sneak a pellet or two in at distance under sudden duress.
 
The type of shot used will also affect the pattern size. From what I've seen, the plated buckshot seems to spread less--probably because it tends to deform less during the trip down the barrel.

I think you're going to have to experiment.
 
I've tested my 11 inch sawed-off SBS Ithaca double barrel versus a 14 inch Model 12 pump SBS versus a 20 inch Mossberg 500, all with cylinder bores. As jmr40 says, there is no difference in pattern size between barrel lengths.

It's been a while, so I don't remember quite what the pattern size was. I wasn't really interested in that anyway, just whether they would be different.
 
That’s interesting. I wonder what load the coach gun was using as it sounds like they experimented and hand loaded something. I have an 18.5 double that will be spread over bmyold Rem 1100 skeet gun; however that is at distance. The Flight Control rounds hold a small pattern out to about 45 yds and that round has been specialized for distance. Sooo
Looks like I must get my diff powders/wads and diff shot out and first see what I can cup-cut and mix to find a spread I like in the 18”. Maybe go to a couple sizes down from buck and run thru the chrono for numbers and go from there.
At 30’, even #4 loads can still do a job on a metal bucket and jump it. 30’ may just be too close to open up.
 
Barrel length doesn't have any effect on pattern. The choke determines the pattern you get. 18" is the legal minimum barrel for a shotgun with 26" minimum overall length. That means most doubles will need to have barrels longer than 18" to meet the 26" overall requirement. The Mossberg shockwave and similar guns fall into a loophole in the law. They are not considered shotguns and have their own rules. I don't recommend those type of guns, but that is another thread.

With a cylinder bore around 1" per foot is the number I've seen thrown around, but I've never tested the theory. If true expect 20" patterns at 20'. Something with interchangeable choke tubes and an Improved Cylinder choke should tighten up patterns. Remington makes an 870 intended for turkey hunting with a 21" barrel that takes choke tubes and is what I have on my HD shotgun.

All of the powder is burned in the 1st few inches in all shotguns. Longer barrels give the pressure generated by the powder more time to accelerate the projectiles and will increase velocity. But there is very little to be gained with shotgun barrels over 18". Stay with a 12.
1” per foot or 1” per yard? I’ve always found it to be closer to that inch-yard spread with cylinder bores. (Flite control wads excepted, those hold a very tight pattern.)

Stay safe.
 
As noted above you've going to need to do a bit of testing (patterning) with whatever shorty you employ - and that goes for the weapon, the round, and the shot size... Some years ago the trainers for Dade county's officers (Miami, etc.) did a bit of testing with improved cylinder bored, standard riot guns using basic 2 3/4" 00 buck rounds and found them to reliably disperse the shot at one inch per yard from the muzzle.... a seven inch pattern at seven yards (one foot past that 20 foot requirement). As a practical matter, it meant that if you weren't aiming - you weren't hitting...

Their means used to demonstrate how it went were sequential targets (just 2 x 3 foot blank white targets placed at 3, 7, and 15 yard intervals, one behind the other in a straight line to show exactly what was happening as that load went downrange. Very enlightening.

Although you may believe you want that pattern to expand as you've indicated... me, I'd want as many of those pellets on target as possible for an immediate end to any conflict... I'd vote for that 7 inch pattern every time - but I'm not an advocate of short barreled shotguns at all... I'd want and prefer a standard riot gun every time, if I had a choice, for close quarters work (since in the real world getting your target to remain stationary isn't something I'd ever expect). No matter what is shown in popular entertainments.....
 
The rounds that do not have a shot cup, a.k.a. wad, will open up quite a lot more at a given short distance than the ones with a wad. S&B and Rio, and I’m sure several others, make rounds without the wad. Federal Flite Control is a well known round with a wad designed to help hold a tight pattern. 12” at 20’ is a big pattern, though. I’d need to measure some of my old patterns but I don’t think your going to quite achieve that wide of a pattern at that short distance.
 
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1” per foot or 1” per yard? I’ve always found it to be closer to that inch-yard spread with cylinder bores. (Flite control wads excepted, those hold a very tight pattern.)

Stay safe.
I believe 1"/ft is what shot shells in rifled barrels spread. That was my rule of thumb for my snake gun when hiking in Arizona.
 
After blasting away with diff loads I started thinking about all being said here. I realized in a dim bulb moment I have always considered shotgunning from a sporting field load perspective; testing diff. Loads and spreads with field shot. Every shotgun barrel is a bit different so patterning helps greatly, though with 00-buck in my 20’ range I haven’t really notice much if any noticable spread, maybe fist sized maximum. I needed to rethink what I want to accomplish, stopping the threat. I do then need the most punch per round with all pellets hitting hard in a small area, and not thinking along a sporting ‘golden bb’ hit.
Thanks all for tweaking my skewed thinking.
Afa shorty shotties, I perfer them with stocks also, tho about an inch under my trigger reach only for ease of maneuverability around a door or a faster swing when (tho I hope never)
I need to hit a threat on the move. I’m getting up there snd find I don’t get a standard shottie moving as quickly as I have in my previous years. Having said that, for the watermelon and cantaloupe Zombies I wouldn’t mind a pretty short barreled double at the range just for the love of noise & blasting away at Fruit gone bad.
 
A Cutts compensator with skeet spreader would give the biggest spread but not 30" at 30 feet. I use one for, duh, skeet.
 
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