Perazzi Back Boring

[MartynB]

remember when we used to shoot 36g Fitasc loads all day long !

20 odd years ago , yes I do . In fact in the garage  earlier this year I found six boxes  of Victory 36gm , the white ones with black hares printed on the cartridge . I used to shoot them , when necessary , through a Dural action K80  , no problem .. It had a Kickeeze pad . I’ve still got that gun.

We put the cartridges in the cupboard under the boiler for a while to make sure they were dry then we shot a few boxes for a laugh. With the same K80 I found the 36 gm unpleasant , through my MK 38 trap and my mate’s old full width 682  , not too bad at all  , Mossberg 500,  hilarious , and through my buddies B2000 gas   auto  we were nearly eating the bolt  ! 

Heavy gun, properly fitted , decent pad , + 28gm = heaven

 

[timps]

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

http://www.claytargettesting.com/Bore_Diameter/Bore_Diameter.pdf

Posting these links for the severalth time.  Perhaps someone will eventually bother to read them.

I have read the first one before and it proves exactly what I am saying is correct.

To quote directly from it.

“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.“

“There was no relationship between recoil and peak shell pressure. In contrast, shot speed and recoil speed were strongly related; the faster the shot, the faster the recoil.”

I go along with that as well as I keep saying I am not on about peak pressure in the chamber but working pressure in the barrel just as the shot and wad exits. It’s lower than peak pressure but what causes recoil is change in momentum, higher working pressure as the shot leaves the barrel means greater force generated due to increased acceleration.

As I have always said tighter chokes can theoretically increase the velocity, the paper you posted proves it, with increased velocity comes increased recoil so the above proves tight chokes also increase recoil. The only question up for debate is can anyone feel that difference, some people say they can and i'm not going to say they cant as I have no idea the  physics and the increase in velocity means it is plausible.  

This paper goes into depth about trying to better measure secondary recoil on rifles not cannons, as I say its not much of an issue with the pressures used in shotguns but an interesting read on the physics side of it and the flaws in testing in a jig rather than on a shooters shoulder when measuring recoil.

http://past.isma-isaac.be/downloads/isma2014/papers/isma2014_0508.pdf

 

[Wonko the Sane]

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

I suspect that is a consequence of the increase in gas pressure as the ejecta hit the impediment of the choke and has little to do with gas speed thru a restriction since the ejecta is for all intents and purposes out of the barrel before the gas gets to the choke area.  A reeeeeeaaaaaalllllllly high speed pressure graph would maybe provide some info on that.

Not that it actually is of any real concern since it is what it is and enlightening as the data and analysis it will remain the same.

 

[timps]

I am a little confused as in an earlier post you said a tight choke would reduce recoil and Mr. Winston demonstrated that choke has no effect on recoil at all.

However, his paper states speed increases recoil and tight chokes increase speed therefore choke has to increase recoil according to his findings.

I’m also not too sure how an increase in gas pressure occurs or how it increases the ejecta speed (velocity) if the ejecta (wad) is out of the barrel before the gas gets to the choke area. The gas is pushing the wad through the choke, it has to be there at the same time exerting a force on the wad to have any influence on itself or the ejecta. Unless you are saying a vacuum exists between the wad and the gas.

As I keep saying secondary recoil is proven phenomenon and Giovanni Battista Venturi wrote a law about choke on gas flow which is the basis of why tighter chokes increase ejecta velocity and also secondary recoil.

The research paper I posted and the subsequent references to other research papers contained in that paper contain all the data and analysis to prove it.

I never ever get into the argument of whether anyone can feel it or not as that is subjective to the shooter. The only reason I posted was to explain the physics behind it, the only reason I keep debating it is people like to say the physics is wrong but offer no proof as to why.

 

[Wonko the Sane]

on gas flow which is the basis of why tighter chokes increase ejecta velocity and also secondary recoil.

Gas flow increasing velocity thru the choke can have no effect on the ejecta since it is long gone.  The pressure spike as the ejecta hit the impediment of the choke area would likely be the reason for increase in ejecta V.  

I’m also not too sure how an increase in gas pressure occurs or how it increases the ejecta speed (velocity) if the ejecta (wad) is out of the barrel before the gas gets to the choke area.

and that is not at all what I said - - see above

 

[timps]

Gas flow increasing velocity thru the choke can have no effect on the ejecta since it is long gone.  The pressure spike as the ejecta hit the impediment of the choke area would likely be the reason for increase in ejecta V.  

and that is not at all what I said - - see above

If you are going to quote me then please quote the whole sentence so it is in context.

My whole sentence was saying the same law that covers why the ejecta velocity increases is also the same law that covers why secondary recoil increases, two separate things but they are connected, what happens to one effects the other and the same law covers both.

According to Giovanni Battista Venturi if the velocity of the ejecta increases due to choke then so does gas flow afterwards therefore primary and secondary recoil have to both increase. 

Your original statement was that the ejecta was out of the barrel before the gas gets to the choke area, regardless of what you meant it is what you said and it is blatantly not true, hence my response in questioning it, .

Ironically when you and I had this very same debate on this very forum in 2016 where I stated that there was a restriction in flow rate caused by the increase in choke. That this restriction would cause an increase in pressure behind the wad as it entered the choke area producing an increased velocity of the ejecta for full choke over cylinder, you said I had a misunderstanding of fluid dynamics, it was Hogwarts physics and that it didn’t happen.

I guess you have changed your mind somewhat since our last discussion on it and believe in Hogwarts physics now, anyway i'm off to backbore my wand.

 

[Wonko the Sane]

Here's hoping that you get more velocity and less recoil from that wand

I suspect that is a consequence of the increase in gas pressure as the ejecta hit the impediment of the choke and has little to do with gas speed thru a restriction since the ejecta is for all intents and purposes out of the barrel before the gas gets to the choke area.

As I mentioned in the first place - the increase in the gas speed thru the choke area has no effect on ejecta V since the ejecta is out of the barrel before the choke has any influence on the gas itself.  Two separate events and the choke may influence the secondary recoil to whatever extent with the increased gas speed but that still is not going to influence the ejecta V.  I apologize for not having any better way to describe that.

 

[timps]

Here's hoping that you get more velocity and less recoil from that wand

As I mentioned in the first place - the increase in the gas speed thru the choke area has no effect on ejecta V since the ejecta is out of the barrel before the choke has any influence on the gas itself.  Two separate events and the choke may influence the secondary recoil to whatever extent with the increased gas speed but that still is not going to influence the ejecta V.  I apologize for not having any better way to describe that.

I’m hoping my wand behaves a lot better thank you.

Wonko you really need to pick up a physics book and read it before trying to debate physics, seriously it would be a good idea.

Newton's laws of motion and certainly Giovanni Battista Venturi will help you. What do you think pushes the ejecta through the choke to increase velocity and what do you think the law is that covers pressure related to velocity increase through a choke? Remember the shot tries to act like a fluid (deformation of the shot and friction aside hence why it tries but is not considered a fluid) it is not a solid lump nor does it behave like one, granular material can and does behave more like a fluid hence the increase in velocity.

Regardless you have kept on stating that velocity of the ejecta would not increase thorough a tighter choke both earlier on in this thread and the one in 2016. Your assertion was that there was no increase in pressure and no increase in velocity but now you have changed your mind.

Your only reasoning was Mr. Winston proved it didn’t increase velocity however when you read Mr Winston’s paper it actually proves that it does.

You were wrong on the velocity increase and dismissed the pressure as a cause of it so why now are you so sure you are right on this when you were wrong on that?

The gas has to flow faster through the choke as the ejecta is travelling 50fps faster than the gas. As I keep saying they are connected and covered by one reaction that must balance due to the conservation of energy. The choke is the cause of increased velocity at the expense of pressure in the choke for fluids and gases.

The pressure is greater at the beginning of the choke but the velocity is slower, the pressure is less at the chokes tightest point but the velocity is greater, it’s the transfer of energy, pressure transferred into velocity to keep the equation balanced. This is the same for both fluids and gasses and as I have stated the shot tries to behave like a fluid through a choke.