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#483837 06/25/17 04:22 PM
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Got into a discussion this AM after a couple rounds of skeet when one of my compadres saw the sorry condition of some of my 20 ga AA's. I understand there is no direct relation of pressure to recoil but it seems there must be some relation of pressure (lower somewhat when the mouth of a hull is cracked and degraded) to velocity. Maybe depending on the burn rate of the powder, the pressure where it counts (near the muzzle, I suppose) and ultimately the volocity of the shot, could be affected by the condition of the hulls.


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I can't remember where I read it, but there were pressure tests done on hulls as they aged. It seems the roughness of the hull interior increases pressure to a degree, offsetting some of the degradation of the hull mouth unable to crimp as well.

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Simple statement, without pressure there would be neither velocity nor recoil.
However the thing often misunderstood is Neither is directly related to "MAX" chamber pressure.
Bottom line is recoil is determined by total ejecta weigh & the velocity it is given, but the velocity of that weight is determined by the Total pressure curve pushing it. Thus both velocity & recoil are controlled by pressure, just not the Max pressure but total pressure.


Miller/TN
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Pressure will be lower if the cartridge does not have a good crimp. I do not remember how much this effects pressure exactly.


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I think 'total impulse' might be a better term Miller.

That is what is represented by the area under the pressure curve. "The work done".

If the pressure never reaches the intended initial value, the area will likely total lower.

Crimp condition and crimp depth both affect initial pressure rise. The shell closure resists the initial payload movement thus allowing the pressure to build up to the design optimum for the powder charge.

A new shell is best, and it's downhill after each firing.

Is it a problem? Not a huge one since shotgun powders are on the fast end of the range of smokeless powders, especially those used for target loads.

Where crimp problems might get serious is when using slower powders in cold weather. It's best to use only new or once-fired hulls for field loads.



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Jones;
You are correct, total impulse is a more descriptive term. Was mainly just trying to make the point that Max Pressure is not the final outcome on this Total Impulse. You can with many loads have more total impulse while maintaining a lower Max pressure.

While I do not actually have the necessities of checking it I do believe that in most cases "IF" using the same identical charge if the max is lowered then the total will be lowered as well. Thus when a weak crimp lowers the initial pressure rise, lowering the max it is also going to result in a lower total impulse thus lowering the velocity as well.
I am thus in total agreement of your assessment of new versus older shells & particularly where slow powders in cold weather come into play..


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I think this is the Tom Armbrust article referring to case life and velocity. Case life has little effect on velocity

http://www.armbrust.acf2.org/caselife.htm

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Most of the answer is in the responses above. But it always boils down to how you want to define "recoil". In its simplest form, total energy ( joules, lbs/foot, etc) of the recoil gives us something we can work with. But we need a lot more before we can tell how it will feel.

Three 7 lb long guns with the same stock-barrel geometry and same butt configuration. One black powder rifle, one Shotgun, and one magnum rifle.

Assume these all fire loads producing recoil of the same total energy. One will always have recoil with higher peak force than the other two. In this example, it's the magnum rifle. It will have a high peak force push the firearm, but it will be for less time than the others. This can clearly be "felt". If you don't believe that, you don't believe in recoil pads and hydracoil systems.

Recoil is force/time, to me. Your definition may be different.

Last edited by Chuck H; 06/26/17 09:25 AM.
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Interesting article by Armbrust.

It reads like an ad for modern components.

Modern components are indeed very good, but...

Only one powder was tested.

Only light target loads were tested.

The concluding comments about weak crimps and field loads with slower powders while traditional common wisdom and undoubtedly correct is not supported at all by his data in the article! He didn't test any!

This whole waste of ink is ONE data point about American Select which is a good powder but hardly universally used. It's not the most cost effective powder, thus has not captured a dominant market share.

I would not extrapolate this to other powders, especially anything with slower 'relative quickness' like Green Dot, Universal, etc.


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Chuck;
What you say is of course correct. "However" comparing a magnum rifle with a shotgun is somewhat akin to comparing apples with oranges.
I do feel this bit of "Felt Recoil" has been much overplayed. For instance for many many years Hercules RedDot was the primary powder for loading the 3-1 1/8 skeet/trap loads @ 1200 Fps. Along in the early 90's I believe it was they introduced a new powder which was very slightly slower than RedDot but faster than GreenDot. Much Ado was made over how this "Slower" powder would reduce the "Felt" recoil. If both powders were loaded to give identical velocities there was less than a grains weight difference in the powder charge. I truly doubt that 1 person in a Thousand could actually "Feel" a difference in the recoil which of course would have had identical recoil energy. There does have to be some amount of difference for us mere humans to detect. Pressure curves for all [powders suitable for loading shot shells are quite close together. One could quite possibly "Feel" a difference between say RedDot & BlueDot, but these two powders are not suitable for loading the same shot weights to the same balilstics.


Miller/TN
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