doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 2.75" shells in 2.5" chambers

Poor old Thomas takes a licking and keeps on ticking. Very good at spitballing explanations for the results of tests which didn't meet the demands of scientific rigor; I continue to believe that the duration of stimulus shorter than response time argument (somewhere about top of p. 238 in the first Gun Book) remains an ingenious and inviting hypothesis. Human beings aren't capable of being certified as calibrated instrumentation so such tests (however methodically scrupulous) are simply flawed in the premise that they are in any way more than a thought problem. Naturally old Gough would jump ahead and begin to think about the contribution of human neurology. Incidentally, how many distinct arguments can dwell on the head of a thread?

jack

Newton says: "for every action, there is an equal and opposite reaction"

I say: pressure drives the acceleration of the payload. Put that together with father Issac's thoughts above. It (acceleration) is traditionally measured over time, by engineers. If there's some other mysterious driver of the payload, besides pressure in a gun, it escapes me.

The "felt recoil test" by Mr. G.T. had how many samples? That was a statistically significant sample of what population? If you took the same number of people, nah! lets say ...the same subjects, and had them shoot a .22 rifle at a quarter flipped thru the air, how many would hit it on the first shot? How many with a .410? 28g? 20g? 12g? Yet Annie Oakley could do it reliably...and Mr. Furgeson can do it with a bow on occasion. Polls and samples that are not statically significant can and do provide misleading information. Even statically significant polls provide only probabilities of outcomes.

The plot of velocity against time (acceleration) of the payload doesn't look like that of pressure against time (expanderation[?]) of the propellant gases. What's that tell us? Me, very little. You? We're sure lucky the old cork ain't moving two directions like in an IC engine or you guys would have lost me by now. OK, you have.

jack

2-p, I, for one, find you thinking, researech, and writing of great value. Debates, such as this one, do best when all points of view pitch in with all their thinking. The issue we have is lack of currently relevant data. As I said, too bad the former writers didn't give us the data behind their reports.

One would not expect the payload velocity vs time plot to look like the pressure vs time plot. The pressure against the base of the wad is converted to force (pressure times area of the wad base; force pounds per square inch times square inches equals force pounds). Force equals mass time acceleration. The mass is fixed, so the acceleration will vary proportionally with the force. So, the acceleration curve will look like the pressure curve. The gun's free recoil velocity and free recoil displacement will be a mirror image of the payload velocty and payload displacement scaled by the weight difference. However, when the gun is held against a human shoulder, the recoil velocity and recoil displacement are probably going to change, even though the acceleration is not changed.

The above is simple physics. How humans will "feel" it is not so simple. Or, so I believe.

Though not a directly applicable analogy, it reminds me of the little survey George Hickox did with an E-collar, in the seminar I took, to show how little electric stimulation was being used on my dog and the others by him when demonstrating proper E-collar use for training. He passed the collar around and had each of us hold it while he started energizing the collar from the lowest setting up to the point where each person could feel it. I could feel a #1 setting, my wife a #3, others couldn't feel anything until much higher settings up to #12. My dog was responding to stimulation #1 on her neck, other dogs no higher than #3 was needed to get a response. Correction settings were around #10 for the dogs. This collar system went up to #50. He sold a lot of those collars that day. this just illustrates the differences between individuals.

I am not sure this is true. It has long bothered me that there are no internal ballistic programs for shotgun with the ability to predict internal pressures. They certainly exist for rifle and handgun loads. One of the best in that arena is QuickLoad. (Although it does seem to have it's weaknesses.)

I reread Ackley, Powley and Hatcher, whose pioneering work lead to the formula's that are used by today's software.

There is a major impact upon internal pressure when the bullet encounters the rifling. The shape and composition of the bullet directly impacts pressure. To more limited extent seating depth and type of seating of the bullet play a role as well.

QuickLoad maintains a database of powders and bullets. For bullets not in the database you must make detailed measurements and enter them into the software.

The culprit here is friction. As the projectile requires more energy to be driven down the barrel, internal pressures will build.

A shotgun shell is even more complex. That is why most reloaders follow a recipe so "religiously". If you change the wad, you change the friction, which impacts the pressure.

Also, this group is probably more aware of internal pressure issues than most around, because of the age of the guns we are usually talking about. My understanding is that internal pressures in a shotgun peak about 16" from the chamber. So has the maximum velocity of the projectile been reached within the barrel?

Pete

Pete, I would think the highest pressure would be in the chamber, just after the powder ignites, where all the gases are constrained in a small space. As soon as the wad starts moving (and space increasing) pressure should drop rather dramatically.

This is just my logical(?) thinking, ;-)

JC

JC; I do believe you are absolutely & totally corect on this. All I have ever seen correlates this. There have been some pressure curves shown here on the board on several occasions taken from data produced by the Old DuPont powder co back in the early '20's with a variety of powders from fast, slow & Black all loaded to the same nominal ballistics. The point of peak pressure varied by little more than ¼" as I recall & all fell within the chamber of the gun. The reason for establishing the point for recording max pressure in a shotgun's pressure bbl @ 1.0" from breech was that if extended much further it could not be counted on to reliably "always" catch the "Peak" of all loads. The tale told for so many years that Smokeless powders reached their peak pressure some 14" down the bbl in the vicinity of the shooters hand was purely a "Scare" tactic used to discourage the use of damascus bbls. The Gunmakers them selves knew better, with the increased use of smokeless they bagan a gradual "Beefing up" of the guns "Breeches".

Pete, just to illustrate my point: this burst was caused by a mix up in the powders used to reload the shell.
The loader inadvertently used smokeless powder in an amount prescribed for a black powder substitute (could it be called PB?).
There was no obstruction.

This was posted here in 2006 together with the injury the poster suffered on his arm. You'll probably remember.


JC