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Ultrastu

Barrel length ?

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So a question to the experienced  and techies .

If a shotgun barrel is significantly shortened say from 30 inch to 15 inches do we get a significant drop in velocity ? 

And yes i know the min. uk limit is 24 inches. 

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These days the powder burns in about 10 inches of barrel, so as long as that is all done you should not see much difference!

Allowing for a warm cartridge in a temperate atmosphere.

Edited by TIGHTCHOKE
Syntax!

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Would a guess do? With black powder yes, the pressure builds up gradually as the powder burns slowly as the shotload travels up the barrel, that is why muzzle loaders had long barrels......with nitro powders being fast burning pressure builds up much quicker, within the first few inches on ignition.

beat me to it TC

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I had a Browning A5 with a 13" barrel many years ago and it was fed solely on Eley Grand Prix 6s, never missed a beat!

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Don't think anything would notice at the receiving end.  We had some Baikal 12g s/s shotguns cut down to 18 inches for tactical use back in the early 70s and they still did the job, mainly with slug but also SGs and some bird shot.

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44 minutes ago, Ultrastu said:

So a question to the experienced  and techies .

If a shotgun barrel is significantly shortened say from 30 inch to 15 inches do we get a significant drop in velocity ? 

And yes i know the min. uk limit is 24 inches. 

Are you thinking of robbing the post office 

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Ok reason i ask is .

Mate has just bought a .410 biakal single shot and put a s&g moderator on the end of it. This makes it a 26 inch barrel and about 6 inches forward of that moderator  with 2 inches reflex behind. 

He also has exactly  the same biakal .410 but the fully shrouded model ,which is drill ported underneath the shroud from about 12 inches (from breech) .this extends about 8 inches infront of the muzzle. 

The logic behind buying the new unported gun (with add on mod ) is so the shot has the full 26 inches of acceleration and hence higher muzzle velocity over the ported version .

So historically out hunting pige, crows etc :- 

I run my yildiz .410 with a 28 inch unported barrel (+ mod ) and I seem to be able to cleanly kill birds much further than my mates ported barrel gun .probably 10 yds further .

The chokes are  similar (with the bialkal being a touch tighter than my yildiz )

This led us to believe that the ported gun robs energy over a non ported gun .

We did some tests between the 3 guns this weekend .my 28 inch 

His 26 inch and the ported at about 12inches .

They all broke clays .at 40 yds 

The ported shot the tightest groups .but on a modeling clay test at 35yds the ported showed slightly smaller holes in the clay (but not by much ) .

Ive watched vids of people testing different barrel lengths on shotguns from 36 down to 8 inch and many sizes in between and with every drop in length there is a corresponding drop in average velocity. 

Using a table of one of these tests the guy found his 26 inch barrel fired at about 1142 fps and an 11 inch barrel 1003 fps  a significant drop in velocity 12% and a corresponding drop in energy of 23 % .

Now im thinking that due to the nature of a ported barrel under a shroud that the pressure in the shroud can get forward of the shot increaseing the pressure infont of the shot and effectively slow it even more than if it were just a open ended 12 inch barrel .

I would ideally need a chrono but dont have one i can shoot a shotty through .

Thoughts ?? 

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Thoughts? Yes I have one, next time you're explaining to someone you missed due to reduced velocity & energy check to see if they're keeping a straight face. :lol::good:

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I have a 410 cut to 1/8th over legal and one with 30 inch barrels. I will try both but will put the open choke on the 30 inch barrel and see what spread and penetration I get to even things up a bit.  I have some old sheets of ply and it will be interesting to see the difference if any in penetration. 

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11 minutes ago, Ttfjlc said:

Thoughts? Yes I have one, next time you're explaining to someone you missed due to reduced velocity & energy check to see if they're keeping a straight face. :lol::good:

Yeah cheers .i have the 28 inch non  ported gun and dont "miss "as much as my mate .

So its not really my problem .

Its just the wondering about the physics im interested in .

2 minutes ago, Walker570 said:

I have a 410 cut to 1/8th over legal and one with 30 inch barrels. I will try both but will put the open choke on the 30 inch barrel and see what spread and penetration I get to even things up a bit.  I have some old sheets of ply and it will be interesting to see the difference if any in penetration. 

Problem with that walker is i dont believe penetration depth is a good indicator of retained velocity or energy .

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7 minutes ago, Ultrastu said:

Yeah cheers .i have the 28 inch non  ported gun and dont "miss "as much as my mate .

So its not really my problem .

Its just the wondering about the physics im interested in .

 

Just having a laugh, how long has your mate been shooting? We all have our limits, maybe it's him rather than the gun? I do believe in what you are saying has an effect to some extent but in real world terms I haven't noticed any difference when I flick between different length guns.

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19 minutes ago, TIGHTCHOKE said:

Surely it could be as simple as your Mate is a poorer shot!

Thats probably more likely the case.

But i like to give him more credit ./ excuse .

5 minutes ago, Ttfjlc said:

Just having a laugh, how long has your mate been shooting? We all have our limits, maybe it's him rather than the gun? I do believe in what you are saying has an effect to some extent but in real world terms I haven't noticed any difference when I flick between different length guns.

Do you swap between a 28 inch and a 12 inch barrel .

Or just from 30 to 32 inch ? 

 

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It should as while in the barrel its still accelerating. When it leaves it starts to slow down quickly. 

How much difference I do t know but won't be much.

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1 hour ago, Ultrastu said:

Do you swap between a 28 inch and a 12 inch barrel .

Or just from 30 to 32 inch ? 

 

You've got me there, mind you I've never had a need for a sawn off. :good:

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1 hour ago, figgy said:

It should as while in the barrel its still accelerating. When it leaves it starts to slow down quickly. 

How much difference I do t know but won't be much.

So in a barrel the shot driven by the wad rides the front of the pressure wave created by the burning powder .the powder burns as the shot is moving driving more acceleration .

And when the shot exits a normal barrel the pressure front exits immediately behind the wad and goes out at 90 % angles and infact accelerates even more and over takes the wad and shot for a short distance (6 - 9 inches approx ) before the pressure is equalized with the atmosphere. (Loud bang at this point too ) .what im interested in is when in a shroud with a ported barrel .does that pressure front driving the wad -when it reaches the first 2 ports accelerate forward down the shroud and increase the pressure infront of the shot at the same time decreasing the preassure behind it . 

I mean the only reason this lead shot is going forward is because the is a massive difference in pressure between the primer and the atmosphere at the muzzle .if the pressure at the muzzle was the same as the pressure at ignition the shot would go nowhere .

.

Im just wondering if by adding these ports under a shroud can reduce velocity further than we would expect .

Oh by the way the difference in heard shot noise between the 2 baikals is so small as not to be worth worring about. 

The add on mod doing a fantastic job its hardly worth having a fully shrouded mod especially if there is a big velocity drop too .

Just saying 

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Ultrastu I understand what your saying about a shrouded barrel with ports. Yes it will reduce velocity of the projectile as you lose pressure behind it.  The speed the projectile is traveling down the barrel won't leave enough time for expanding gasses to go out through the port and put pressure into the barrel.in front of the projectile as it's going to an open end. Also the projectile has kenetic energy to keep it moving so losses by porting are not as great as we would first assume.

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Your right figgy .

I think any excess pressure that gets infront of the shot is going to be venting /expanding towards the open muzzle faster than the shot is travelling and hence the amount of pressure that can effectively act backwards  on the shot is small and probably of little consequence .still this does mean that the barrel if ported from  say 12inches is gonna act as just the same (or very similar) to a normal 12 inch barrel and have the equivalent drop in velocity .

Cheers guys. Thanks for listening and helping me think out loud. 

Stu 

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There are a lot of things that can increase or decrease velocity the question is whether the drop is meaningful in the real world.

In terms of barrel length and porting most of the meaningful acceleration is carried out in the first few inches however like you say if there is a pressure differential behind the wad then there is a force still acting on the wad therefore it continues to accelerate but at a reduced rate compared to the first few inches.

If the ports are so large, they are able to dissipate all the pressure before wad reaches the end of the barrel the wad will slow due to friction. However, if the ports don’t dissipate all the pressure it will continue to accelerate but at a reduced rate depending on how much pressure is dissipated.

In terms of figures Neil Winston found that in a 30-inch barrel that there was enough workable pressure to cause increase in velocity between full choke and cylinder due to  Giovanni Battista Venturi’s principle:-

“The average increase in the measured speed through the full choke compared to the cylinder choke is about 50 fps.”

“The speed-increasing effect of choke began with the smallest constriction, 0.005 inches. As the degree of choke increased, so did the speed,”

“the tighter the choke, the faster the reported speed.“

http://www.claytargettesting.com/study2/pages/study2a.html

Now in the real world 50 fps difference is nothing but it does prove there can be a difference in velocity at the end of a 30” barrel due to pressure. Therefore dissipating this pressure by ports will cause a decrease in velocity, whether this is ever noticeable to the shooter is a whole other question.

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On 17/02/2019 at 11:07, B725 said:

Are you thinking of robbing the post office 

😂😂😂

On 17/02/2019 at 10:22, Ultrastu said:

So a question to the experienced  and techies .

If a shotgun barrel is significantly shortened say from 30 inch to 15 inches do we get a significant drop in velocity ? 

And yes i know the min. uk limit is 24 inches. 

Give your FLO a bell & ask him what he thinks 😀

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6 hours ago, timps said:

There are a lot of things that can increase or decrease velocity the question is whether the drop is meaningful in the real world.

In terms of barrel length and porting most of the meaningful acceleration is carried out in the first few inches however like you say if there is a pressure differential behind the wad then there is a force still acting on the wad therefore it continues to accelerate but at a reduced rate compared to the first few inches.

If the ports are so large, they are able to dissipate all the pressure before wad reaches the end of the barrel the wad will slow due to friction. However, if the ports don’t dissipate all the pressure it will continue to accelerate but at a reduced rate depending on how much pressure is dissipated.

In terms of figures Neil Winston found that in a 30-inch barrel that there was enough workable pressure to cause increase in velocity between full choke and cylinder due to  Giovanni Battista Venturi’s principle:-

“The average increase in the measured speed through the full choke compared to the cylinder choke is about 50 fps.”

“The speed-increasing effect of choke began with the smallest constriction, 0.005 inches. As the degree of choke increased, so did the speed,”

“the tighter the choke, the faster the reported speed.“

http://www.claytargettesting.com/study2/pages/study2a.html

Now in the real world 50 fps difference is nothing but it does prove there can be a difference in velocity at the end of a 30” barrel due to pressure. Therefore dissipating this pressure by ports will cause a decrease in velocity, whether this is ever noticeable to the shooter is a whole other question.

Thankyou very much for that reply and good food for thought 

Cheers 

Just now, blackbird said:

😂😂😂

Give your FLO a bell & ask him what he thinks 😀

Why ? Is a degree in physics a requirement to get a job as an FLO ? 

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