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Old September 26, 2012, 12:51 PM   #1
300magman
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Barrel Length and Shot Velocity

I had a thought while looking at a few 20 guage shotguns yesterday. Does the length of the barrel matter much with shotguns, when it comes to the velocity of the exiting shot?

As a reloader with a chronograph and software I know that an extra few inchs of barrel can give most rifle cartridges a good boost in velocity, but I wonder with the nature of shotgun powders and thier extremely large internal bore volumes (relative to rifles) whether the same is true for loads of shot. Especially since I am also unsure as to the quality of seal between the bore and the wad/shot cup, I could image there is more blowby than in the average rifle.


Anyway, if anyone's curious I just ask because the little wife wants a shotgun for upland birds and waterfowl now that she is officially a hunter.
I know my 3.5" 12ga waterfowl loads will knock her over, so my thoughts immediately went to a 20 ga. (which is about perfect for grouse anyway)

My choices are one barrel for both purposes or one shorter lighter barrel for grouse and another 4" to 6" longer heavier barrel for waterfowl. The weight of the longer barrel would help somewhat with recoil, but unless it also has some advantage in velocity then I don't think the extra cost is justified.
{and if you have to ask why I would want more velocity for waterfowl hunting then you haven't spent enough time shooting worthless steel shot at nervous, over pressured geese...I find the first bird at 25 yards explodes, the next at 35 is a good kill, and the last at 45 isn't fully penetrated and often has some fight left...I've at times had bite marks to prove it...oh how I miss LEAD}
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Old September 26, 2012, 01:29 PM   #2
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Not that much of a difference in velocity. This is a personal preference, but on a pump or autoloader a 24-26" barrel is a good compromise. I generally use 26" for everything, including waterfowl. Longer barrels help with a smoother swing much more than velocity. For a pure waterfowl gun a longer barrel would help a bit on longer passing shots. Not because of velocity, but balence, a smoother swing and longer sighting plane.

The shorter 22"-24" guns are quick pointing for grouse or quail where birds are fying straight away, but give up something on passing shots To me the 26" is just the perfect all around length on a repeater. On a double, because of the short receiver a 28" gun gives about the same balance and overall length.
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Old September 26, 2012, 01:53 PM   #3
yadkin
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I agree totally with jmr40 in all aspects most of your shotgun powders even mag powders are fast burning and it does not take much bbl. length to burn it up.
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Old September 26, 2012, 02:17 PM   #4
300magman
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I suspected as much. I will probably get her to handle a few of my favorites and see if anything has that "feel" that she likes. . . . I'm hoping for another 870.
Pumps just feel like the best option for a new shooter to me. They can be fast (unlike singles and bolts) but without the worry of having another live round ready to go off (like doubles or semis), if she gets excited and forgets to immediately click the safetly back on.
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Old September 26, 2012, 05:21 PM   #5
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I suspect she'll be way happier with a decent gas operated semi-auto than a pump gun or any fixed breech gun. The gas operation system - will reduce the recoil a lot ...and there are a lot of guns out there...that aren't too heavy for her...maybe with a 26" or 28" barrel even in a 12ga ...should be fine for her. Length of Pull - seems to be a bigger deal for a lot of women / depending on how long her arms are...but there are some models made for more petite ladies or young shooters with shorter lengths of pull.

In the used market ...I'd look for a good clean Remington 1100 or 11-87 ..maybe a Browning Gold - or a Beretta 390 or 391. There are lots of them around.

In the new market ...under $1,000 there are a lot of options...Browning Silver hunter is a nice gun - some of the Beretta 391's are under $1,000...maybe even find one of the old Browning Gold models ( Gold is only in 10ga now / but there are still some out there - new in boxes at very good prices).

A gun with a 3" chamber is plenty in my view....and don't go to really heavy loads if you can help it ....waterfowling is where you might not have a choice / but too many of the 3 1/2" magnum loads ...in anything but the softest shooting semi-auto will not be fun for her to shoot.
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Old September 27, 2012, 05:46 PM   #6
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As a fellow reloader with a chrono and 27 types of shotgun powder I have to disagree on a couple of the statements. It boils down to burn speed and shot load. Not all slhotgun powders burn at the same rate and I have several that take a full 30 inchs of barrel to get a full burn and 32 inchs of barrel to get top speed from lthe chrono.
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Old September 27, 2012, 05:52 PM   #7
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Olddrum1, my friend, thanks for the heads-up.
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Old September 27, 2012, 06:49 PM   #8
BigJimP
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Holy Cow Oldrum .....does some of that old powder burn better...if you take the twigs and pine needles out of it ..??

( you might be right ...I just couldn't resist ) - I've never done any tests on burn rates / just mindlessly repeating the stuff I've read...or that I can remember....
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Old September 30, 2012, 09:28 AM   #9
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BJP, Buffering is the correct terminology for twigs and pine cones. Makes the crimp look better and the campfire is started when I reach the game. Adds bulk and speeds up the burn rate on some of these slower powders.
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Old September 30, 2012, 02:34 PM   #10
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I seem to recall some tests the NRA did a good while back. They took, IIRC, a Marlin Goose gun with a 36" barrel and chrono'd it, then picked up the hacksaw. Cutting the barrel in 1 inch increments, they'd shoot a field load,chronograph 10 shots, then cut again.

Between 18 and 30", there was more variation between shots at a given length than between 18 and 30". Velocities at 16" almost mirrored those at 36".
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Old September 30, 2012, 09:39 PM   #11
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I remember reading a article some years ago where they took a single shot 12 and started whacking the 22-inch barrel down by 1 inch at a time to check velocity and it did start dropping off until they got under 14-inches. I found it hard to believe at the time. I don't remember what kind of loads they were shooting, but I woudl suspect magnum loads could make use of a little more barrel than 14-inches
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Old September 30, 2012, 11:43 PM   #12
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Cutting the barrel off using a run of the mill Walmart load proves little in that its a fast burning powder usally. The burn, i believe, is complete shortly after the shot colum leaves the forcing cones. you get into something like Winchester 570 and then whacking off an inch at a time will become more relevant. Also with some of these powders temperature will also make a difference.
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Old October 1, 2012, 06:06 AM   #13
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The longer the barrel the more velocity...its simple physics.
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Old October 1, 2012, 06:36 AM   #14
Brian Pfleuger
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Quote:
Originally Posted by Pistolgripshotty View Post
The longer the barrel the more velocity...its simple physics.
Simple physics that turns out to not be true.

The powder eventually stops creating more pressure than the bullet/barrel friction.

Some cartridges (typical handguns) this number can be as low as 12-15 inches. 22 rifles might be around 16-18 inches. Many small capacity rifle cartridges might stop gaining speed around 22-24 inches.

No reason shotguns would be different. Longer does not always mean faster.
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Old October 1, 2012, 06:39 PM   #15
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The NRA American Rifleman Dope Bag Staff did the Marlin Goose Gun test.

They attached a choke and fired the gun for pattern and velocity, then cut off one inch, reattached the choke and tested again.
They continued to cut off in one inch increments until they were down to 12 inches.

Their results:

Anything that's going to happen ballistically in a shotgun barrel happens within about 18 inches.

The only advantage of a longer barrel is that it points better.

Anything over 28 inches and you actually start to loose velocity due to friction.

Barrel length has zero effect on patterns. An 18 inch barrel will pattern as well as a 36 inch.

Things didn't "Start to get out of hand" until it was down to about 12 inches.

The idea that a longer barrel will shoot farther or "harder" is a left over from the days of black powder when a longer barrel burned the powder more effectively.
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Old October 1, 2012, 07:39 PM   #16
Jim Watson
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The old Churchill gunmakers of England did extensive tests many years ago.
They concluded that 25 inch barrels on a traditional SxS game gun gave full velocity, good patterns, enough forward moment of inertia for a smooth swing, and with their tapered rib, as good alignment on the target as longer barrels.
They sold a lot of Model XXVs on that basis.
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Old October 3, 2012, 03:15 PM   #17
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I found this on another Forum

Quote:
Hm, I'm going to bump this sorta old topic to say that I've chronoed some slugs through a Mossberg 500 Serbu. In an 18.5" barrel, standard Remington 1 oz. slugs were doing 1410 fps. Through the Super-Shorty, 1140 fps. That's less than a 20% velocity loss. Reduced recoil was, coincidentally, 1140 fps through the 18.5" and 920 fps through the Serbu, once again less than 20% loss. It wasn't my chrono, though, so I only shot slugs through it.
taken from RyanM on THR forum.

The Super shorty is a 6.5 inch barrel compared to an 18.5 inch barrel.

Unless I am mistaken the slugs would be effected by barrel length more than shot.
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Old October 3, 2012, 04:25 PM   #18
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IIRC U.S. Customs (before it became ICE under Homeland Security) conducted in-depth tests on shotgun barrel length for use in helicopter ops. The concluded that all the powder that was going to burn efficiently would do so in 14 inches.

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Old October 4, 2012, 09:44 AM   #19
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Yes and No... Simple physics my dear :)

As mentioned, it depends on the powder burn rate. Target loads use fast burning powder, so longer barrels offer no increase in velocity. Heavy goose loads use slower burning powder and need 30" to provide good burning and pressure. Dove and quail loads use quick burning powder. Pheasant loads vary by brand, Winchester shells are softer hitting on the shooter due to slower powders used.
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