An aspect of physics, and how it relates to rifles

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shredder4286

New member
I posted this in "The art of the rifle" because the topic came about while shooting rifles.

I noticed while at the range last week that there is a huge difference in recoil between my Savage Model 14 .243 Win and my Mossberg 4x4 30-06- EVEN THOUGH the .243 was loaded with 40 grains of Varget, and the 30-06 was only loaded with 1.4 more grains of the same powder. Both rifles wear a wood stock and are around 8 lbs. The bullets were a 70 grain Nosler Ballistic Tip varmint, and a 165 grain Prvi Partizan SP BT.

Now- I was with the understanding that more powder = more recoil, but that wouldn't make sense in this case because the amount of extra recoil from the 30-06 in comparison to the .243 was more than equaled the small amount of powder difference. My shooting partner's theory was- the heavier the bullet- the more you'll feel it in your shoulder. What came to mind was- for every action, there is an equal and opposite reaction. Is this correct?
 
Your partner is correct. Recoil is a practical example of conservation of momentum. The weight of the 30-06 bullet is double that of the .243. This accounts for the difference in recoil.
 
Heavier bullets= less powder and more felt recoil. For the same caliber, as you increase bullet weight the load decreases (and so does velocity)- or chamber pressures can increase beyond what they are designed to handle.

The first time I deviated from my 174 grain BTHP's to a 200 grain soft point hunting bullet the felt recoil from the heavier bullet weight was quite noticeable...
 
The rifle's momentum is always equal and opposite to the bullet's momentum plus the momentum of the powder gasses.
The rifle's recoil energy is not equal to the bullet's energy however.

Basically, if the rifle weighs 100 X the bullet, the rifle will have 1/100 the bullet's energy after firing. Let's say, the bullet has 1000 ft-lb of energy, then the rifle will have 1000/100 or 10 ft lb of recoil energy plus whatever the powder gasses add to it.

Double the weight of the rifle and make it weigh 200 X the bullet and now the rifle will have 1/200 the bullet's energy or 1000/200 = 5 ft lb of recoil energy + the contribution of the powder gasses.

If you really want to see this principle in action, consider the fact that a .223 shooting a 55 grain bullet has a bullet energy very similar to a 1 1/8 ounce 12 gauge target load. However, the 12 gauge handily outkicks the .223.
 
Not a comment about rifles but I believe something in a similiar light as far as physics are concerned. Earlier today I was testing out some new bullets I had cast and loaded in .38 Special. I fired some first in a S&W .38 Special J frame 2" snubbie, then in a S&W .38 Special Police & Military with 4" barrel and finally in my Dan Wesson .357 Magnum with 6" barrel. All bullets were the same 158 grain with the same amount of powder. The difference in felt recoil between the 2" snubbie and the Dan Wesson was quite noticable due to the weight of the pistols. The Snub nose I had to hold with both hands and the recoil was quite snappy. The Dan Wesson I could easily hold with one hand and the recoil was minimal. Naturally the barrel lenght was not the same, someone more educated on this might comment, but the major difference in felt recoil was I believe due to the weight of the pistols.
 
Not a comment about rifles but I believe something in a similiar light as far as physics are concerned. Earlier today I was testing out some new bullets I had cast and loaded in .38 Special. I fired some first in a S&W .38 Special J frame 2" snubbie, then in a S&W .38 Special Police & Military with 4" barrel and finally in my Dan Wesson .357 Magnum with 6" barrel. All bullets were the same 158 grain with the same amount of powder. The difference in felt recoil between the 2" snubbie and the Dan Wesson was quite noticable due to the weight of the pistols. The Snub nose I had to hold with both hands and the recoil was quite snappy. The Dan Wesson I could easily hold with one hand and the recoil was minimal. Naturally the barrel lenght was not the same, someone more educated on this might comment, but the major difference in felt recoil was I believe due to the weight of the pistols.
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If you really want to see a contrast, shoot that ammo out of a rifle chambered for .357 magnum.
My Marlin Cowboy II is ultra pleasant to shoot, even with hot .357 magnum loads.
 
The rifle's momentum is always equal and opposite to the bullet's momentum plus the momentum of the powder gasses.
The rifle's recoil energy is not equal to the bullet's energy however.

Basically, if the rifle weighs 100 X the bullet, the rifle will have 1/100 the bullet's energy after firing. Let's say, the bullet has 1000 ft-lb of energy, then the rifle will have 1000/100 or 10 ft lb of recoil energy plus whatever the powder gasses add to it.



Double the weight of the rifle and make it weigh 200 X the bullet and now the rifle will have 1/200 the bullet's energy or 1000/200 = 5 ft lb of recoil energy + the contribution of the powder gasses.
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So is this formula what people use to generate "recoil tables" to compare the felt recoil/recoil energy of different calibers/rifles? How do you figure out how much the powder gas is actually adding to the felt recoil?
 
How the recoil is spread out makes a difference in perceived recoil too.The smaller and thinner the handgun grip the less spread out is the push back through your hand(s). With the rifle you're taking some recoil through your hands and a lot back through your shoulder. I had a custom built .45-70 Rolling Block, I had the butt stock made 1/2" wider than normal. It made a huge difference in felt recoil.
 
Yep. Heavier bullet equals more recoil. A 1oz shotgun slug equals 437gr.

Shoot that out of a NEF and you will know all about recoil.
 
The answer seems to have been explained very well already, but I like to explain by saying if you stand still and push a little kid, the kid just falls over. If you stand still and push someone the same size as you (using the same amount of force as before) both people move about the same amount. Using the same amount of force again, if you stand up against a wall and push, you fall over backwards and the wall doesn't move.

Bullets are the same. the heavier the bullet, the more resistance that is pushed back onto you.
 
shredder4286 said:
So is this formula what people use to generate "recoil tables" to compare the felt recoil/recoil energy of different calibers/rifles? How do you figure out how much the powder gas is actually adding to the felt recoil?
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The propellent's contribution to recoil is not simple to figure out but it is not insignificant either. Rules of thumb are often used but a rule of thumb that's reasonably accurate for a deer rifle may not be accurate for a shotgun or a varmint rifle.
In a shotgun the powder only weighs about 1/20 as much as the bullet and so it's contribution to recoil is far lower than a varmint caliber such as the .220 swift, where the powder may actually weigh more than the bullet and so the majority of this rifles recoil actually comes from the powder charge.

Also, you can't assume that the speed of the powder gasses is the same as the bullet. I have heard some experts claim that you can assume 4500 fps for the powder gasses, but that again is a rule of thumb that is valid only if you stick to common deer rifles. In a shotgun, the pressure has dropped so low by the time the shot leaves the muzzle that the velocity of the powder gasses is likely much lower than that.
 
Weight of the rifle plays a role in "kick" as well as bullet weight. In general, heavier rifles will "kick" less, heavier bullets will "kick" more. Powder charge plays a role too, but in your example the .243 total weight exiting the barrel (powder and bullet) is 110 grains. The .30-06 total weight is 206.4 grains. In equal weight rifles the .30-06 should kick about 2X the .243.
 
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Comparing grains of powder between different calibers is not meaningful because you are dealing with different volume. Volume in this case is the volume of the case with a given bullet seated to a given depth. The pressure created and the bullet weight, altered slightly by how tight the case neck is (crimped or not, etc) determine velocity achieved. Those are also factors in felt recoil, in addition to the weight of the rifle, ergonomics of the stock, how the rifle is rested, and shooter technique.
That is my layman's explaination, which some of the experts on here who are lots smarter than me may wish to expand on or debunk. ;)
 
I suppose it relates to physics somehow but in addition to all of the above, the design of the rifle, as well as handguns, also enters into the matter, too. I am refering here only to "felt recoil," not measured recoil. They aren't the same thing as I see it and the idea even applies to artillery pieces. In the case of tube artillery weapons, however, the differences are in the behavior of the piece when fired.

In the case of rifles, it is in stock design that the differences appear. A straighter stock would, in theory, have less muzzle rise than one with a more traditional drop. That was the idea behind the original design of the AR-10, although I think the idea was not original with Armalite. The slightly earlier British experimental bullpups had a similar stock design. The German machine guns MG 34 and MG 42 could be said to have straight stock designs. Still, I say "in theory," because the difference in felt recoil with heavier and heavier cartridges will probably be less and less. After all, a straight stock does not change any of the laws of physics. It just uses them to achieve certain other objectives, mostly a straighter recoil dynamic. But with the 5.56mm, it becomes practically unimportant.

With handguns, weight distribution is important. A heavier barrel will seem to have less kick, all other things being equal, but it probably is only noticeable in a revolver.
 
There are a number of implementations of recoil-calculating formulas available on the web. One of these is: http://shootersnotes.com/articles/taming-recoil/
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Good link there, definitely an interesting read.


Volume in this case is the volume of the case with a given bullet seated to a given depth. The pressure created and the bullet weight, altered slightly by how tight the case neck is (crimped or not, etc) determine velocity achieved. Those are also factors in felt recoil, in addition to the weight of the rifle, ergonomics of the stock, how the rifle is rested, and shooter technique.
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So, let's say- I had a .243 load with the bullet seated .015" off the lands, exactly 40 grains of powder and a 100 grain bullet- the case full-length resized. I also have a 30-06 load with the bullet seated .015" off the lands, exactly 40 grains of the same powder and (my manual only lists down to a 110 grain bullet for the -06, so that's as close as I can get there) a 110 grain bullet, full length resized case. Given they were shot through rifles of the same weight and design, you're saying the volume of the 30-06 case would still cause there to be significantly more recoil, even though all these other factors were virtually identical?
 
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