Pressure in a shotshell

[Big Friend Ten (BFT)]

Paul,

My previous posts included such information as:

Young's Modulus stating "Everything is a spring".
http://parkerguns.org/forums/showthr...ng%27s+modulus

This is measured by the Birnell hardness of a substance.
http://parkerguns.org/forums/showthr...hlight=brinell

Also, any opposition to the acceleration of the shot column will raise pressure. It has to because the powder is burning at a rate that increases under pressure.

[Big Friend Ten (BFT)]

Originally Posted by Pete Lester

I think I gave a pretty good example of the effect.

Pete,

Sorry, but I reread your posts in this thread and did not see it. Please include a link or the information in this thread for consideration.

Mark

[Bindlestiff]

Originally Posted by Pete Lester

Case in point. Sherman Bell's data for the Short Ten shows a Fed Hull, Win 209 primer, 32gr of SR7625 with SP10 wad and some filler for both 1 1/4 ounce lead and 1 1/4 ounce of Bismuth. The lead load uses a folded crimp and generated 6700 psi. The Bismuth load using a Roll Crimp (which reduces pressure) generated 7100.

When loading shells, the shot is measured by volume and listed in ounces. I suspect the volume/ounce conversion is for lead. Do you think Sherman weighed or measured his Bismuth load? If he measured the shot and given Bismuth is less dense than lead, the Bismuth weight would be lighter than 1 1/4.... but generated higher psi. What would that indicate?

[J.B. Books]

Originally Posted by Mark Ouellette

Pete,

Sorry, but I reread your posts in this thread and did not see it. Please include a link or the information in this thread for consideration.

Mark

It is from Sherman Bell, check the last page of the Short Ten spreadsheet I put up this week.

[J.B. Books]

Originally Posted by Robin Lewis

When loading shells, the shot is measured by volume and listed in ounces. I suspect the volume/ounce conversion is for lead. Do you think Sherman weighed or measured his Bismuth load? If he measured the shot and given Bismuth is less dense than lead, the Bismuth weight would be lighter than 1 1/4.... but generated higher psi. What would that indicate?

Since Bismuth loads are stated in weight and not volume I have always used an adjustable bar or a modifed mec bar that throws the desired of weight of Bismuth. I have never heard of anyone doing otherwise.

An equal weight of bismuth to lead is going to have a taller shot column.

PS. I am pretty certain Sherman weighed his Bismuth loads, the evidence is the difference in amount of filler wad needed for the same weight loadings vs. lead.

[Mark Garrett]

It is ( or should be ) standard procedure to weight all shot charges . Even with lead shot that is a different size or antimony will weigh different if thrown be volume . All shot bushings should be adjusted to throw your shot charges to the correct weight . Thought that was common knowledge.

[Cold Spring]

Originally Posted by Paul Harm

From a Accurate Powder Co. reloading handbook :
The fundamental difference between a shotshell and a typical center fire rifle cartridge is, that the efficiently of the shotshell is 100% dependent on the round itself. By this we mean that all the " resistive forces " must be generated within the confines of the round itself. No assistance is provided by the gun.
The reason for this is that the Maximum Peak Pressure is reached long before the base of the shot/wad assembly has left the the case. [ In the case of a CF rifle cartridge, the peak pressure is achieved when the bullet is engraved, therefore the large contribution, as a result of leade/free-bore dimensions on the combustion process. [ ie. bullet/bore interface fit, bullet hardness, bearing surface, etc].
The reason for this is that the critical engraving force which is so important to the dynamic combustion process present in a CF rifle cartridge is totally absent in a shotgun.
This means that the efficiency re ignition and the subsequent increase in pressure, is totally controlled by the integral configuration and assembly of the round itself. These constitute the main internal mass [ shot mass ], the internal volume [ wad design ], the dynamic collapse [ primary expansion ] of the internal volume [ collapsible section of the wad], plus the displacing of the internal assembly and the unfolding of the fold/crimp [ secondary/final expansion].
The way this COMBINATION interacts, will determine the efficiency Pressure impulse [ profile and time-base ] and the Peak-pressure vs Velocity [ P/V ]. The resistive force, presented by friction in a shotgun is negligible.......

I was just quoting the reference attributed to Accurate Powder, who surely has objective modern data to substantiate what is written. It's copied in part above; please especially note the last sentence. I have a hard time understanding a substantial increase in bore friction because of a 1/4" or so longer shot column OF THE SAME WEIGHT riding in or mostly in a plastic wad.

I certainly subscribe to the advice that all should stick to published recipes for bismuth shot by reliable industry sources.

[Mark Garrett]

"These constitute the main internal mass [ shot mass ], the internal volume ."

1 oz of Bismuth has more internal volume and mass of 1oz of lead.

[Paul Harm]

I've always thought peak pressure was created within the shot shell , or at most, within the first couple of inches. With that said, Pete's comments about a higher shot column equals more friction, hence higher pressures. Pete also wrote in the Loading the Short 10 on page two :The difference betwen equal weights of Lead vs Bismuth is the height of the shot column and amount of surface area in contact with the bore. 29gr of 7625 is 29gr of 7625. With the lead load you generating 5900 PSI. Nice shot has the same size shot column as lead, but because it's harder than lead it generates more pressure as it has a harder time squeezing down through the forcing cone. This puts you up around 7400 psi with a fold crimp. Using a roll crimp will drop pressure, maybe 600, maybe 800 maybe even a 1000. Only testing will tell for sure. I would stay with the low pressure lead load and add 1500 psi. I can't imagine a sound Parker 10ga having an issue with an 8000 psi load. If you go too low you risk bloopers, especially in cold weather. -- I'm more than happy to agree with " friction in the barrel " meaning " friction in the forcing cone trying to squeeze ".

[Big Friend Ten (BFT)]

Paul et all,

In a shotshell PEAK pressure is created in the chamber.

In a rifle peak pressure is created when the bullet is forced, essentially swagged, into the rifling.

When reviewing pressure curves notice that peak pressure of a shotshell occurs early in the curve as measured in time. Remember that the shot column is traveling rather slowly at peak pressure in comparison to muzzle velocity.