Pressure in a shotshell

[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.