Pressure in a shotshell

[Kensal Rise]

For the enjoyment of all, I post this older pressure reference:

[Big Friend Ten (BFT)]

Thanks John!

The above chart is measured in inches from the breach. I'd love to have one of those test barrels!

For all 4 powders the peak pressure is reached no more than 1 and 1/2 inches from the breach. That distance is not far from the top of the powder charge as measured from the base of the shell. Hmmm, maybe that's why the chambers of barrels have much thicker walls than do the rest of the barrels...

[J.B. Books]

Originally Posted by Mark Ouellette

Thanks John!

The above chart is measured in inches from the breach. I'd love to have one of those test barrels!

For all 4 powders the peak pressure is reached no more than 1 and 1/2 inches from the breach. That distance is not far from the top of the powder charge as measured from the base of the shell. Hmmm, maybe that's why the chambers of barrels have much thicker walls than do the rest of the barrels...

"That distance is not far from the top of the powder charge as measured from the base of the shell". Which coorelates to the shot charge starting to enter the forcing cone and meeting resistance. Longer more gradual forcing cones have long been recommended for reduced felt recoil, lower pressure, better patterns. Along with longer forcing cones there is overboring.

"Over-boring reduces friction between the wad and the barrel as the wad travels from the chamber through the bore and out the muzzle. This reduction in friction is generally thought to reduce felt recoil and deformation of the shot pellets which results in improved pattern integrity and an increase center-pattern density."

http://www.doncurrie.com/over-boring...-forcing-cones

[J.B. Books]

"Friction being the highest of all the secondary force action on the wad/shot column as it moves down the barrel."

"My reasoning here is that the shot under acceleration of this force would try to spread out. Image trying to pile up shot on the top of your reloading bench the shot under just 1g of acceleration would rather spread out than stack."

http://mcb-homis.com/shotgunpressure...npressure.html

[Kensal Rise]

This is all grand discussion. However, it must always be kept in mind that currently fashionable "long forcing cones" are something to be avoided in good double guns. This includes Parkers. Why? Because to make the forcing cone long, the reamer removes metal where it is most needed. And in well-struck double gun barrels, that can result in dangerously thin wall thickness. Best to stick with standard forcing cones and a bit more "felt recoil."

[Paul Harm]

Pete, first problem is that Mr. MCB is an engineer . I don't believe I've ever read such a long drawn out article trying to explain perceived recoil. And in it he makes a couple of assumptions. I fail to see how it relates to the discussion here about pressure increases with hard shot. If peak pressure is generated within the chamber [ and it is ], then friction between the wad and barrel is nill. Friction causing higher pressure would be an assumption unless someone has tested along the barrel. Then we would have higher pressures for quite a distance. JMHO

[J.B. Books]

Originally Posted by Paul Harm

Pete, first problem is that Mr. MCB is an engineer . I don't believe I've ever read such a long drawn out article trying to explain perceived recoil. And in it he makes a couple of assumptions. I fail to see how it relates to the discussion here about pressure increases with hard shot. If peak pressure is generated within the chamber [ and it is ], then friction between the wad and barrel is nill. Friction causing higher pressure would be an assumption unless someone has tested along the barrel. Then we would have higher pressures for quite a distance. JMHO

The article points out friction is a factor in pressure. Hard shot has more difficulty hence resistance to flow from the chamber into the forcing cone, so what he is saying is more outward pressure is exerted on the sides of the barrel walls. Increase in friction, increase in pressure. Bismuth is harder than lead, steel even harder. Both have lighter mass than lead so the shot columns are taller. They both exert more pressure in the direction of the barrels and over a greater surface area as compared to equal weight of lead. The top of the shot column is jamming up at the beginning of the forcing cone holding back the rest or it in the chamber and that is where you have the highest pressure.

[Bruce Day]

So we have long discussions about perceived recoil, which by definition cannot be measured because if it could, we would have a formula to measure it. And we have a perfectly good, it seems, recoil formula which to my knowledge has stood unchanged for over 100 years.

With the elusive perceived recoil, one person may perceive it and another may not. It may be elusive as the Higg's bosun particle. Or it may depend on how may cups of coffee the shooter had.

[Paul Harm]

Bruce, the thread started out about what causes pressure in a shotgun shell and went to perceived recoil. Perhaps I misunderstood Pete's claim about friction in a barrel being a factor in pressure. I could believe hard shot doesn't compress as easily as lead when going through a forcing cone so higher pressures would be a result. I don't believe going down the barrel has anything to do with higher pressures. When writing instead of talking to someone face to face, sometimes it's hard to explain/understand exactly what is meant. I started the thread mainly to bring to every ones attention how important the crimp is and how it changes pressure.

[Bruce Day]

Paul, yes the thread drifted. And yes, crimp depth does affect pressure. However, when we are discussing Parkers, chamber pressure, in my opinion, should play little part unless a person is seeking to load up to maximum service pressure. We know what or about what those are for each gauge, but most of us, myself included, seldom shoot max pressure shells. The Parker max service load is more than we want or generally need to shoot, but its there if we need it unless the gun in question is loose, bored out, bad stock or otherwise in poor condition. I don't have guns like that but I know some do.

We have posters who somehow seize upon 5000psi as a magic number for 12ga chamber pressure. I don't know where that comes from, maybe light 2 " British guns, but not Parkers and its not a Parker number at all. Parker told us what to shoot with a range of acceptable loads which are still available today. For me, that's what I follow.