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Originally Posted By: Stan
Originally Posted By: 2-piper
Pressure does not enter into the formula for calculating recoil at all, only motion & wt.


I agree with all of your statements concerning recoil and pressure and their effects on the gun, Miller. And, as far as "calculating recoil" goes, with the above statement, too. Calculations, however accurate, do not totally agree with what I perceive the recoil to feel like.


Stan the problem with quantifying perceived recoil is that it depends upon very subjective evaluation on the part of the individual experiencing the recoil event. As you know no two human nervous systems are exactly alike so what may be perceived by a strapping young fellow as mild recoil may be perceived by an old duffer such as myself as a sever recoil event but after taking a couple Alievs I might find the same recoil impulse to be only moderate.

Last edited by TwiceBarrel; 08/07/09 12:17 AM.
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I'm using red text for my answers to try and keep question and answer close together. DF, I'm answering your specific questions only here. General answers will follow.

Originally Posted By: David Furman

On the right fork is a greasy guy with slicked-back hair and a truckload of ammo that reads:
calculated recoil=almost zilch
Chamber pressure=SAAMI Max
This guy tells me that if I take his fork in the road, I can have his truckload of ammo to shoot my gun to my hearts content.
WHAT WILL HAPPEN TO MY GUN IF i TAKE THIS ROAD AND SHOOT MY GUN TO MY HEARTS CONTENT?? Most likely, at SAAMI max, the barrels will not blow out or bulge. However, wear to the action between the bolt and bites and between the hook and hinge pin (and bolt to bites of any third fasteners) will be accelerated. When the joints are tight, the grinding rate will accelerate. Once looseness develops, battering will become an increasing issue.

On the left fork, is another guy--dressed in somewhat unfashionably old clothes and smoking a pipe--with a wagonload of ammo that reads:
calculated recoil=hope you have a heavy gun with a thick recoil pad
chamber pressure="It's a miracle, but nice consistent ignition in any weather, 500psi (yes, five HUNDRED psi)"
The guy tells me that if I take the left fork I can take the entire wagonload of ammo to shoot my gun to my hearts content.
WHAT WILL HAPPEN TO MY GUN IF I TAKE THIS ROAD AND SHOOT MY GUN TO MY HEARTS CONTENT?? Wear to the action will be minimul, only slightly more than unfired cycling. The stock head and your shoulder will take a beating, assuming the gun is fired from your shoulder. If the stock is of marginal strength, it may split along the grain or at a defect to the grain. If/when the stock develops some looseness in the joint to the action, it will start battering and will soon crack.
Assume my stock wood is just fine and the recoil is a non-issue ot the shooter, I'm only concerned about the gun or any issues caused by the gun. Which road is better for my gun? The one in the middle where both pressure and recoil are kept within reasonable limits for the given gun. Which road will cause my gun to "shoot loose" faster assuming it's well-maintained in all other respects? Metal from pressure and wood from recoil. Why? Because the metal joints must lock to contain the pressure and because the wood must transmit recoil force to the shooter. What are the best books or references that might help one learn about this in order to make my own decisions? With intent to NOT be a smart a$$, the motion issues are from physics, the gas pressure from gas dynamics, and the steel and wood issues from mechanics of materials - all non-gun specific engineering books. Google is a wonderful source for specific topics.

Last edited by Rocketman; 08/07/09 08:07 AM.
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Mike, I'm inserting answers into the quote in red to help keep Q & A close, yet separated.

Originally Posted By: mike campbell
Originally Posted By: Rocketman
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. The action and barrels lock shut to contain the pressure of firing. They experience the same conditiions with or without something absorbing the recoil force. If the gun were fired in a gravity free vacuum, the gun and ejecta would go opposite directions at velocities that conserve momentum until each encountered some other force. The barrels and action would not know if they were fired on typical earth conditions or in the foregoing vacuum.
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." Recoil force exists within the gun only when the gun encounters something, typically the shooter's shoulder, that retards rearward motion and, thus, absorbs the rearward force. Joint looseness allows differing velocities between adjacent parts and allows for one to impact the other; battering.
Your second paragraph covers "movement, grinding, and battering" (metal wear) without using the word "recoil." Intentionally as these issues have to do with relative motion between adjacent parts that are joined.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? No, the stock battering depends on motion of whole gun. If the gun were allowed to recoil freely, there would be not recoil issues with the stock (other than the weight of the stock and that would be a very minimul issue). The action would experience the same issues fired freely or with recoil travel retarded.
Is it not true that it is recoil force transmitted to poorly mated metal surfaces that causes their grinding, battering, loosening, i.e.; wear? No, it is pressure forces.

If not, then it's CHAMBER PRESSURE and NOT RECOIL that causes the pin and hook to be battered? Yes, it is. Clear as mud. Any better? If you need additional explaination, let me know.

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What we're neglecting here, I think, where pressure is concerned is that a burst is not the ONLY possible negative result of shooting overpressure loads. That's the "shade tree gunsmith" view of proof: Work up a heavy load, put it in the gun, secure the gun to a tire, tie a string to the trigger, and go hide behind a tree. If the barrel doesn't burst or the gun otherwise fly to pieces, you're good to go. But that's not the way proof is done by the proofhouses. They also do something called "view" or "inspection", measuring for minute changes that may have occurred after firing--even if the barrels are still intact. If proofloads--which are, obviously, far in excess of service pressure--can cause such minute changes without resulting in catastrophic failure, than why cannot a SAAMI max load of 11,500 psi also cause minute changes (especially if used thousands of times) in a gun with a designed service pressure of 9,500 psi? If pressure is not an issue but recoil is, then that means I'm better off shooting a 1 oz load using 18.5 grains of Red Dot in an STS hull, 10,900 psi/1255 fps (courtesy of the Alliant book) rather than a 2 1/2" Eley Hawk VIP Game, 1 oz, 1300 fps--the latter producing higher recoil because of the greater velocity (but loaded to the lower CIP service pressure standard).

I think we also need to remember, especially as we approach SAAMI max service pressure (as in the above example) that although many of the loads Sherman Bell tested in his DGJ article showed a pressure increase of only a few hundred psi when fired in a short chamber, others approached (and at least one even exceeded) an increase of 1,000 psi. Factor in the variation from one reload to another, you could end up well over SAAMI max service pressure--and, worst case, not that far below original proof pressure of an older shotgun. (Which is why it's a very good idea to err on the side of caution when reloading for vintage guns. Fortunately, that's very easy to do for the 12ga in particular.)

Last edited by L. Brown; 08/07/09 09:02 AM.
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Ok, I'm going to throw my $.02 in....

I haven't seen anything mentioned about powder burn rate. Assuming equivalent payloads and velocities, I would expect that a faster buring powder would create higher peak pressures. My rationale is this: Pressure is created by expanding gases. If the area the gas expands into is larger the pressure will be less. With a slower buring powder the "ejecta" starts moving down the barrel as pressure increases thus increasing the expansion area and resulting in a lower peak pressure. I would also expect the "felt" recoil with a slower buring powder to be less for similar reasons.

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[quote=L. Brown If pressure is not an issue but recoil is, then that means I'm better off shooting a 1 oz load using 18.5 grains of Red Dot in an STS hull, 10,900 psi/1255 fps (courtesy of the Alliant book) rather than a 2 1/2" Eley Hawk VIP Game, 1 oz, 1300 fps--the latter producing higher recoil because of the greater velocity (but loaded to the lower CIP service pressure standard).
[/quote]

Yep. Correct. Exactly!

Although your example is not the finest, beacuse the free recoil energy is a trivial 6% different between the two.


Here's a better example right out of your Alliant data...

1 ounce @1250 fps, pressure 10,900 psi

1 3/8 ounce @ 1250 fps, pressure 7,800 psi

Which one would is better for your 7 lb doublegun, Larry?

High pressure and 17 ft lbs of recoil or loooooooww pressure and 36 ft lbs?

You've professed respect for Miller's expertise; here's his take again....

"I could just as easily point to 2 3/4" 12ga loads of 1oz/1200fps vs 1¼oz/1330fps; both @ an identical 9,500 psi. the lighter load simply "Will Not" "Shoot the Gun Loose" as quickly as will the heavier one even though both have an identical chamber pressure."


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Good question, Mike.

First of all, I don't like 1 3/8 oz in a vintage 12ga, because the max load available in my 1940 Shooters Bible for the 2 3/4" 12ga is 1 1/4 oz. Assuming we're talking a gun with original short (2 5/8", in the 12ga) chambers, which was the genesis of this discussion, heaviest load available for those was 1 1/8 oz. Thus, I interpret that load as being inappropriate for the gun--certainly for the stock, if not for the metal--and seriously inappropriate for the guy on the butt end of the gun.

However, I'd also avoid the 1 oz load like the plague. Add in a little extra pressure because of the too long hull, maybe a little more because my reloader dropped a little too much powder--I'm over current SAAMI max pressure. And way over max pressure for a gun built with short chambers.

In other words . . . two bad choices. And while I appreciate Miller's expertise, I also appreciate Rocketman's. And the fact that both SAAMI and CIP focus on PRESSURE standards, not RECOIL standards. That in spite of the fact that recoil has increased significantly with modern loads--some of which pack 1 5/8 oz of shot into a hull that, back when those vintage guns were built, contained a maximum of 1 1/4 oz. (That's half an ounce more than was offered in the short 12ga hulls--at the same velocity of 1250 fps that the maximum 1 1/8 oz load achieved in the 2 5/8" hull.) With all that additional recoil (but note, still within SAAMI pressure standards) . . . why aren't our modern doubles shooting loose, if that's what happens as a result of recoil?

Last edited by L. Brown; 08/07/09 11:26 AM.
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Originally Posted By: Rocketman

If not, then it's CHAMBER PRESSURE and NOT RECOIL that causes the pin and hook to be battered? Yes, it is. Clear as mud. Any better? If you need additional explaination, let me know.


Thanks, but I don't think you could explain it so I can agree.

Recoil is the movement of the gun, which is the sum of its parts. And it is recoil of these independent parts that accelerates wear on both wooden and metal parts.

Many posters seem to readily accept that it's the recoiling barrel/action assembly as a unit which traverses a few thousandths gap and slams into the immovable object, which is the stock head and imparts damage to the wood.

Yet these same posters cannot accept the fact that it is the recoiling frame being thrust backwards over a few thousandths gap and slamming into the immovable object, which is the hook welded to the barrels, that imparts damage to those metal parts.

Pressure is a necessary condition for the generation of recoil, but is insufficient for quantifying it. And while high pressure without recoil can wear/fatigue/rupture the chamber, it cannot induce greater wear on moving parts (hinge/pin/stock head) except to the extent that it imparts higher recoil energy to those parts.

I can't explain it better than that.


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Originally Posted By: L. Brown
. . . why aren't our modern doubles shooting loose, if that's what happens as a result of recoil?


Gee, I don't know, Larry.

Maybe it's because Sarasquetas and Huglus are built so much better than my 1920's Foxes?


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TwiceBarrel, You are absolutely correct in your stated question! My thinking on the effect of these two forces on an OLDER gun may have been limited to the current and future use of the gun rather than it's past use. Assuming an "older" gun was used extensively with heavy shot charges and pressures common in the years following its' manufacture, recoil most certainly could have an effect on all parts you mention. If this were the case I would think that wear would show now, but perhaps not? In terms of current use of and older gun, appropriate ammunition should be used to prevent or minimize wear. Of couse most things that get used, even appropriately, wear. Speaking only for myself, my statements on pressure and recoil should be taken merely as a warning as to the possible result that could occur if some caution is not taken when choosing ammunition for a shotgun that may have been manufactured when lower pressure shells were used, but also keeping in mind that older wood may break and can be exspensive to replace.

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