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Old July 20, 2012, 03:10 PM   #1
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Recoil Impulse: Am I Missing Something?

I was function(for my pistols not terminal ballistics) testing some SD ammo today, Federal HST 124gr, Hornady Critical Defense 115gr and Speer GoldDot 124gr +p.

Now I understand that recoil as it is perceived is highly subjective. However objectively the GoldDot out of those loads should have the highest recoil impulse.

Out of both pistols I was using(p226 and m&p9c) the HST load seemed to have noticeably more recoil than the CD or GD loads. I'm not even sure I could tell a difference between the CD and GD loads, which by the numbers, should have been the largest variation in recoil impulse.

Am I missing something?
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Old July 20, 2012, 03:23 PM   #2
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Assuming similar muzzle velocities and bullet weights... it might have something to do with the powder used and how complete of a burn that powder has during it's time in the barrel. In other words, what the pressure curve is relative to barrel length... where it "peaks" and at what point before the bullet exits the barrel.

Or... it could just be how fatigued you were when you fired the various loads.

That's all I got.... I'm interested in what others may have to say about this as well.

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Old July 20, 2012, 08:54 PM   #3
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Knowingly or unknowingly, you hit upon part of the answer when you referred to "recoil impulse." Impulse is a measure of the change in momentum over time. In other words, assuming the same weight bullet and powder and the same muzzle velocity of two loads, one will have a greater impulse if it achieves velocity faster than the other load. The total momentum (and kinetic energy) transferred to the gun and shooter are the same. The one with a greater impulse will feel like it has a "sharper" recoil. This is easier to feel when shooting different calibers but I suppose you might be able to feel it shooting different manufacturers' loads due to how fast the powder burns.

Creeper may also have hit the nail on the head when he mentioned shooter fatigue.
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Old July 20, 2012, 09:52 PM   #4
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Hmmm, I had considered that it might be different burn rates, but also hadn't thought that would have created such a noticeable difference. I don't think it was fatigue, I shot 4-5 shots of each type through 2 pistols(30 rounds or so fired) just to get a feel for them and if any obvious feeding issues would occur, before doing some more purposeful shooting with the rest and some regular range fodder.

Maybe I can find someone locally with a chronograph, I'm pretty sure all three are factory tested with a 4" barrel. My m&p 9c is just under at 3.5" and my 226 is just over at 4.4". I could get a rough idea of where the acceleration peaks using information from both of those and the factory data. I don't think any of my other pistols have a barrel between 3.5" and 4.4".

Given that even the more pronounced recoil of that HSTs was still plenty manageable, if they do accelerate faster and come close to the factory spec at 3.5" it would preclude the need to try more +p or short barrel specific ammo.
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Old July 20, 2012, 10:16 PM   #5
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This is apparent when shooting .44 mag and .45 Colt with same bullet weight at same velocity. There is less "impulse" and less felt recoil with the .45 Colt in guns of same weight due to lower pressure in .45 Colt.
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Old July 21, 2012, 12:11 PM   #6
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There's recoil energy and recoil velocity. The recoil velocity means the recoil comes fast [more of a punch ] or slow [more of a push] .You may have two equal recoil energy cartridges with different recoil velocities . The slower velocity recoil will be more comfortable to shoot.
In semi-automatic guns some recoil systems have a definite spike of recoil in the cycle that is less comfortable than one without the spike even though the recoil energy of the two are equal.
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Old July 21, 2012, 12:29 PM   #7
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The only other factor which was not mentioned in the previous posts that I can think of is the powder charge weight differences in the different cartridges.

If the pressure over time does not account for the differences, perhaps pulling the bullets and weighing the powder for each type of cartridge might reveal that the mass of powder is significantly different. This powder mass goes out the barrel and comprises part of the felt recoil.

Merely weighing an unfired loaded cartridge would not account for the differences in case weight.
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