John,
It is a pleasure to continue this pursuit of information!
Yes, I think that it is likely that because the pistol is unconstrained the pressure rises more slowly, as the energy can be dissipated in the acceleration of the pistol to the rear, this may delay the obturation of the bullet and the sealing of the bore, which might actually lower the peak pressure.
In actuality we may have less energy to deal with.
I know some will find this hard to believe, considering the velocity with which the bullet leaves the barrel. The fact is though, as I understand it, for every action there is an immediate equal and opposite reaction. Perhaps the amount of energy is not changed, but I think that the dynamics of the work being performed over time may have been.
Photos in the 30s have repeatedly "proven" that the gun is in recoil prior bullet departure from the barrel. (I think there are such in Ed McGivern's Fast and Fancy Revolver Shooting).
(I will check this evening and repost if not, does anyone know where we might find a picture which shows the recoil or lack thereof, as the bullet exits the muzzle?)
My experience with both rifle and pistol indicates to me that I can change the point of impact by how "hard" I am holding for both rifle and pistol.
My coach (USMC retiree Claire Carlson) tells me the reason for my poor performance at 600 yards with service rifle is that I am not consistently in the same position. This lack of consistency has several effects, all occurring at once.
The point of impact (POI) may change because of the way I am looking at the sights in the prone postion.
POI may change due to a change in the harmonics of the rifle as I place vary pressures on varing points of the stock(s).
The POI may change as the rifle is allowed to recoil to a greater or different manner than a consistent hard hold might.
I "know" for a "personally determined fact" that if I hold a .45 service pistol hard that I have to change the sights versus using a "soft grip".
I am convinced that this is primarily due to a change in the amount or amplitude of the recoil prior to the bullet leaving the barrel. Nothing except the amount of grip is changed here. the elbow does not break, the sight picture is exactly the same, the sight alignment the same. The change in POI appears to me to be solely due to the amplitude of recoil prior to the exit of the bullet from the barrel.
There are about 4 to 6 clicks difference for me between the two grips (at 50 yards). What this "tells" me is that the additional "mass" added by the hard hold lowers the point of impact and requires a "higher" sight adjustment.
If the pistol is allowed to recoil freely, the energy which would have taken a path of lesser resistance and cycled the slide, may in the case of the soft grip be used in pushing the pistol rather than the slide/barrel assembly into recoil relative to the grip frame. This is the theory which I explain the observed phenomenum of "limp wrist" failures.
In theory that flattened primer might be the path of least resistance when the pressure pulse is allowed to freely dissipate in both pushing the bullet through the bore and pushing the entire pistol to the rear. This may allow the pressure curve to flatten in time covering a longer period with a lower peak.
This may cause the unobturated primer to slam back into the breach face hard enough to yield the observed pressure signs. The primer is unobturated due to the energy of the initiation of the movement in response to rising pressure being allowed to work on two vectors rather than one, which delays the full engraving of the bullet into the bore and the subsequent delay of pressure may rob us of some velocity.
Some shooters I know claim that a rifle shoots "harder the harder that you hold it". Is this a observation of this phenomenum in action?
I am not a kinetic physicist but I know that in cutting structural members with explosives a "tamped" charge (one that is contained on the side opposite the desired work direction) can accomplish the same work with less explosive than an untamped charge.
This is a long reiteration of what Walt said much more succinctly, his brevity is admirable.
I should think it would be very interesting to explore what this particular load is doing in your test piece. Have you duplicated this several times? If this is repeatable perhaps, as you indicate, you may have to reevaluate your position on "limp wristing".
John, as one shooter to another, I appreciate your taking the time to back up your impressions with an actual test.
As we begin to evaluate the results the first thing that the scientific community will want to know is what was the number of rounds measured. "Is the sample of sufficient size to allow us to draw a valid conclusion?"
As you are undoubtedly in the same position as the rest of us, not independently wealthy, you might find the idea of doing such an exhaustive test daunting. Now that you are retired, perhaps time and range access are not constraints.
Perhaps you might want to conduct tests and submit an article to one the more esoteric gun rags, using that recompense to offset the expense associated with testing. I would be glad to assist you in the development of the article, the test methodology, or in editing, merely for a credit (should you deem my effort worthy of such). Remember that am I not a physicist, nor a writer, and most certainly not an editor. But I am available! ;-)
Hope that we can continue to explore this, for you now have raised a real valid question for some of us. "What does happen after the hammer falls and before the bullet leaves the barrel?" "In a recoil operated system does lack of firm grip (hold) contribute to malfunctions?"
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Ni ellegimit carborundum esse!
Yours In Marksmanship
michael
[This message has been edited by Michael Carlin (edited 12-22-98).]
