What influences recoil

2005 Views 11 Replies 6 Participants Last post by Ruger Collector, Dec 27, 2007

knayrb

Discussion Starter · Dec 24, 2007

(The stupid things I think of in my spare time). My degree is not in physics but I have taken a few classes on the subject and I'm not as stupid as I look. :?

Newton's 3rd law of motion states that "For every action there is an equal and opposite reaction" This means that if a bullet is coming out of a gun with a certain force there must be the same force applied on the opposite direction. Some of that force is absorbed in the weight of the gun and your body because of Newton's first law which is "An object will remain at rest, or continue to move at a constant velocity, unless an external net force acts upon it." The rest is found in the kinetic energy of the traveling bullet I think.

This got me thinking about the different types of ammo. Let's take a .357 magnum with Federal ammo for example. Federal makes 2 flavors of Premium Personal Defense Hydra-Shok JHP for that caliber. The 158 gr. has 539 ft/lbs of energy at 1240 fps. The 130 gr. has 574 ft/lbs at 1410. Now what I don't get is the 130 gr. with more energy and velocity is rated as their Low Recoil version. What gives? How can the the more powerful round have a lower recoil? Am I not including the weight of the bullet in the equation? I thought that the energy measurement would include the mass if the bullet and velocity.

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UtahRSO

· #2 · Dec 25, 2007

It's not kinetic energy that determines recoil, it's velocity times bullet weight, or in other words what is called the Power Factor. Assuming the same gun weight and powder weight (just to keep those variables constant), and using the muzzle velocity and bullet weight of your example,

130 X 1410 = 183,300
158 X 1240 = 195,920

So the 158gr @ 1240 is going to have about 7% more recoil than the 130gr @ 1410. Of course the weight of the propellant and pressure of the load influence recoil as well (sometimes a lot), but the Power Factor is a quick way to compare recoil of various loads.

(OK, for you physics people, I recognize that mass and weight are really different items, but I'm not making this that complicated.)

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Car Knocker

· #3 · Dec 25, 2007

And then there's perceived recoil, which is independent of actual recoil.

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xmirage2kx

· #4 · Dec 25, 2007

Mjolnir said:
It's not kinetic energy that determines recoil, it's velocity times bullet weight, or in other words what is called the Power Factor. Assuming the same gun weight and powder weight (just to keep those variables constant), and using the muzzle velocity and bullet weight of your example,

130 X 1410 = 183,300
158 X 1240 = 195,920

So the 158gr @ 1240 is going to have about 7% more recoil than the 130gr @ 1410. Of course the weight of the propellant and pressure of the load influence recoil as well (sometimes a lot), but the Power Factor is a quick way to compare recoil of various loads.

(OK, for you physics people, I recognize that mass and weight are really different items, but I'm not making this that complicated.)

And to think, I never thought I would need math in real life.

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· #5 · Dec 25, 2007

Recoil is the result of accelerating mass. See Newtons Third law of motion.

To get an idea of what recoil will be like for a specific caliber and load I suggest you refer to http://www.hornady.com/images/ballistic ... charts.pdf

The link is Hornady's PDF for ballistic data; the field you are interested in is muzzle energy. Hornady used to publish it in their reloading manual volume 2 but they have since moved to a one volume manual absent this information.

Bear in mind a recoil event in a rifle is much longer than a pistol or shotgun. Rifles use much slower burning powder than shotgun and pistol so the recoil event is much longer (although without significant trigger time it is hard to perceive the difference).

If we have a pistol generating 2000 ft/lbs (enough energy to move 1 lbs 2000 feet or 2000 lbs 1 foot). 2000 ft/lbs is a very big pistol, I don't think the likes of 454 Casull exceeds this (it may I am to lazy to look it up). Compared to a rifle generating 2000 ft/lbs, a fairly small rifle (about par with a small Varmint rifle).

The felt recoil of the pistol will be much greater. The whole event happens by the time the bullet exits a much shorter barrel (we use fast burning powder in this case as we have to exhaust our powder charge in a shorter time with a much shorter piston for gas expansion). While the rifle typically has a barrel 3x as long and consequently we use a slow burning powder to keep building pressure behind the bullet as it travels down a much larger piston (the barrel). This of course explains why the longer the barrel the faster the projectile (a bullet exiting a 10" barrel will be traveling faster than a bullet exiting a 7" barrel, provided they are the same load).

Of course there are exceptions to all of these examples. short barreled rifles often have barrels nearly as short as a large pistol and people will adjust loads accordingly.

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Ruger Collector

· #6 · Dec 25, 2007

knayrb said:
The 158 gr. has 539 ft/lbs of energy at 1240 fps. The 130 gr. has 574 ft/lbs at 1410. Now what I don't get is the 130 gr. with more energy and velocity is rated as their Low Recoil version. What gives? How can the the more powerful round have a lower recoil?

To put it in simple terms, without mentioning numbers, assuming the only variable to be the bullet weight. It's the energy of the blast following the path of least resistance. The heavier the bullet, the more resistance, more resistance in one direction forces more energy into other directions.

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· #7 · Dec 26, 2007

Ruger Collector said:
knayrb said:

The 158 gr. has 539 ft/lbs of energy at 1240 fps. The 130 gr. has 574 ft/lbs at 1410. Now what I don't get is the 130 gr. with more energy and velocity is rated as their Low Recoil version. What gives? How can the the more powerful round have a lower recoil?

Click to expand...

To put it in simple terms, without mentioning numbers, assuming the only variable to be the bullet weight. It's the energy of the blast following the path of least resistance. The heavier the bullet, the more resistance, more resistance in one direction forces more energy into other directions.

Wrong.

It is the result of accelerating mass. You have to have both total acceleration and mass to know the recoil.

It is very clear when comparing the recoil of a 45 colt with a 250 grain bullet and a 300 win mag with a 180 grain bullet... which has more recoil?

Since the projectile is starting at 0 or near 0 all we really need to know is achieved velocity and mass. Unless we want to calculate the duration of the event then I would recommend reading what I wrote above.

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knayrb

Discussion Starter · #8 · Dec 26, 2007

It's not kinetic energy that determines recoil, it's velocity times bullet weight, or in other words what is called the Power Factor. Assuming the same gun weight and powder weight (just to keep those variables constant), and using the muzzle velocity and bullet weight of your example,

130 X 1410 = 183,300
158 X 1240 = 195,920

So the 158gr @ 1240 is going to have about 7% more recoil than the 130gr @ 1410. Of course the weight of the propellant and pressure of the load influence recoil as well (sometimes a lot), but the Power Factor is a quick way to compare recoil of various loads.

So what I'm learning here is that the manufactures are correct in rating certain bullets as lower recoil. Though I think you wouldn't notice that much difference between the 2 loads at only 7% less recoil.

Another question down this line of thinking is stopping power. Is this where the ft/lbs of energy comes into play? Could you have a lower recoil round that has better stopping power? I'm assuming that the bullet expands enough and doesn't exit so that all the energy is transferred to the BG.

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Ruger Collector

· #9 · Dec 26, 2007

Eukatae said:
It is very clear when comparing the recoil of a 45 colt with a 250 grain bullet and a 300 win mag with a 180 grain bullet... which has more recoil?

Do you really consider that a fair comparison? You're changing a little more than the bullet weight...

Eukatae said:
It is the result of accelerating mass. You have to have both total acceleration and mass to know the recoil.

Exactly. That's why a blank round has no felt recoil, no mass (just a few gr of paper) to resist the flow. The energy is following the path of least resistance. The more resistance to the flow of energy the more the energy is forced to go in other directions. Too much resistance (like in this lead fouled barrel), and recoil may be the least of your concerns.

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natehunts

· #10 · Dec 27, 2007

knayrb said:
Now what I don't get is the 130 gr. with more energy and velocity is rated as their Low Recoil version...How can the the more powerful round have a lower recoil?

The question I have is what are they comparing their "Low Recoil version" to. Are they comparing it to another 130 gr. load that they have had, or all of their other loads in that caliber such as the said 158 gr. load?
That is an important point to be clarified.

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knayrb

Discussion Starter · #11 · Dec 27, 2007

The question I have is what are they comparing their "Low Recoil version" to. Are they comparing it to another 130 gr. load that they have had, or all of their other loads in that caliber such as the said 158 gr. load?
That is an important point to be clarified.

natehunts,

Follow this link http://www.federalcartridge.com/ballistics/Ammo_Search.aspx to see what I was talking about. I'm not sure, but I think they are comparing just the 2 rounds in their Premium Personal Defense line. That's what confused me at first.

In my bedroom gun, a .357 with a 6" barrel, I have gone back and forth on the 125 gr. and 158 gr. Speer Gold Dot Personal Protection rounds. I currently have the 125 gr. loaded because I read this: http://www.chuckhawks.com/ammo_by_anonymous.htm. I'm truely trying to understand external ballistics.

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Ruger Collector

· #12 · Dec 27, 2007

natehunts said:
The question I have is what are they comparing their "Low Recoil version" to. Are they comparing it to another 130 gr. load that they have had, or all of their other loads in that caliber such as the said 158 gr. load? That is an important point to be clarified.

Here are some numbers from Modern Reloading Second Edition (2007 printing). They show the high pressure created by the increased resistance of the heavier bullet with less powder (and that if you use as much powder as is possible with a lighter bullet you could easily create a dangerous over-pressure).

These are listed as â€œnever exceedâ€ loads said:
Caliber. Powder type/grains, bullet grains, pressure (PSI).

460 WBY MAG. ACCUR-2700/122.0, 350, 53000.
460 WBY MAG. ACCUR-2700/114.0, 500, 64700.

300 WIN MAG. H4831/84.0, 110, 57363.
300 WIN MAG. H4831/64.0, 220, 62578.

357 SIG. ACCUR-2/7.9, 88, 39100.
357 SIG. ACCUR-2/5.3, 147, 39800.

45 ACP. ACCUR-7/13.3, 155, 20200.
45 ACP. ACCUR-7/10.5, 250, 20900.

25 AUTO. HP38/1.8, 35, 17900.
25 AUTO. HP38/1.5, 50, 17900.

The ISPC Power Factor mentioned by Mjolnir is great for measuring the recoil difference in the same size of gun without knowing the exact chemistry inside of the load. The reason for the two different classes has to do with scoring. A 9mm typically has much less recoil then a .45. This way, the playing field is somewhat equal. However, a 9mm bullet can still make major. On the other hand, it'll have much harsher recoil then a minor 9mm. The reverse can be applied to the .40 S&W. It can be shot in the minor or major class depending on the PF. This is where reloading is a big bonus.

IPSC PF = wt * V / 1000

Where: wt=weight in grains, and V=velocity in fps

Major is from 175 up.
200 gr. .45 bullet at 900 feet/second = 180 power factor.

Minor is from 125 to 174.999.
125 gr. 9mm bullet at 1000 feet/second = 125 power factor.

But it doesnâ€™t factor in a change to the weight of the gun. The 34oz Ruger P90 will have less felt recoil than the 29.6oz S&W M&P45 from the same load because of the increased weight of the gun.

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