doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Pressure vs recoil in old guns

Oil soaking didn't help that stock. ;-)

Larry, I edited to set my comments apart in red. Also, yes, I went further into wear to locking parts and attributed this to pressure rather than recoil.

Post back if it is still not clear.

So, higher pressure will increase wear on the hinge pin, more than increased recoil will?

The picture I posted above is from a 1931 article about the establishment of SAAMI. I thought it was pertinent to this discussion because you see that it is set up to measure pressure, recoil and velocity.

Since all have been mentioned in this discussion and at UJ I thought I would show that SAAMI recognizes the interrelation of the three and has from the time SAAMI was established.

Recoil per se doesn't exist within the gun since the barrels and stock are locked to the action. However, there is a force transmission to any object interfering with the free recoil of the gun. The weak point in the force transmission from the action to the butt is at the stock head and wrist. If the recoil force is too high, you can literally split the wood. And, if the stock develops any looseness, you will get battering of the wood. We would be more correct to say the stock is damaged by transmitting recoil force.

Wear to the hinge pin/hook during firing can occur from battering or relative movement. Battering occurs where there is a bit of off-face so the hook gets a run at the hinge pin. Any strain movement between the hook and pin will result in surface grinding. The action will bend slightly during firing and this changes the position of the hook relative to the pin; maybe only a fraction of a degree, but enough that there is movement. Clean, high pressure lube will minimize metal to metal contact and fine particle grinding, but can't completely eliminate it. Tight on-face, along with hard surfaces on the pin and hook minimize battering.

Let me know if that is not clear.

Not perfectly clear, especially when I try to reconcile this post with the earlier statement...

"Larry, I edited to set my comments apart in red. Also, yes, I went further into wear to locking parts and attributed this to pressure rather than recoil."

Which seems to exclude recoil as a source of wear to locking parts.

You say "recoil force doesn't exist within the gun..." and later in the same paragraph refer to "battering of the wood" and the crux of the paragraph seems to say that "transmitted recoil force batters the wood."

Your second paragraph covers "movement, grinding, and battering" (metal wear) without using the word "recoil."
Is or,is not, this movement, grinding and battering of metal parts "within the gun" due to the same "transmitted recoil force"
that batters the stock?

Is it not true that it is recoil force transmitted to poorly mated metal surfaces that causes their grinding, battering, loosening, i.e.; wear?

If not, then it's CHAMBER PRESSURE and NOT RECOIL that causes the pin and hook to be battered? Clear as mud.

I am also having trouble reconciling those statements. First no recoil then where does the battering come from? Just how does that happen and how is it pressure related since recoil is generated as per Newtons 3d law of motion and no matter how you calculate it pressure plays no direct part in producing recoil?

For your information or a reminder the following is the formula for calculating recoil:

E= 1/2(Wr/32)(WbxMv+4700xWp/7000xWr) squared

E= energy in foot pounds
Wr= weight of gun in pounds
Wb= weight of whot and wad
Mv= muzzle velocity in fps
Wp= weight of powder in grains


You will plainly see there is no element called pressure.

Lastly in your reply to Larry brown you state "Larry, I edited to set my comments apart in red. Also, yes, I went further into wear to locking parts and attributed this to pressure rather than recoil."

How does pressure which is totally contained withing the chamber and barrel act of the locking parts without any direct contact?

I'll stick with the pre-Rocket "pretty well" summation by Ben and Pipes. Little bitty ejecta go one way damn skippy; big ol gun don't come back all that fast but since it's usually about 96 times as heavy as ejecta it comes back for real no matter how you "perceive" the event. That's a Newtonian moment; it's equal and oppo; it's recoil. All that business from Rocket about battering and hammering and is the gun "unitized" thru the stock head, etc. is fine but recoil is sufficient as an immediate cause. Pressure may be the primum mobile in putting a lot of expanding gas between piston and cylinder head but all that stuff moving is enuf to explain mechanical wear without introducing Caspar the unfriendly ghost in the machine.

jack

Rocketman, thanks. Thought maybe the additional comments were yours, but wanted to be sure.

SAAMI lists available loads for the various gauges, including shot charge and velocity (which are the most important elements in recoil). However, if we look at what's happened in the shotshell world over the last few years, we can see that recoil has increased significantly--especially because there are now much higher MV lead loads out there than in the past. (I pattern tested some 12ga, 1 1/4 oz 1500 fps loads. Ouch.) In spite of those increases in recoil, the standard established by SAAMI remains focused on pressure. That is to say, as long as those loads fall within the acceptable service pressure ceiling of 11,500 psi, they're good to go with SAAMI. Seems to me that, assuming recoil threatens the integrity of a gun--even cumulatively, over time--SAAMI would establish some sort of recoil ceiling as well, limiting maximum shot charge and velocity. The fact that they have not done so indicates to me that they consider recoil of any load that falls under their service pressure ceiling to be a non-issue for any shotgun that passes current SAAMI proof (19,000 psi, for 12 and 16ga). Yet obviously, since the standard they set is one of pressure and not recoil, they don't consider pressure to be a non-issue.

If a shotgun were held dangling on a string, and a cartridge fired, what would it do? It would accelerate equally and opposite to the cartridge ejecta.
As one piece, bound inseparably.