# How does bullet weight effect recoil?



## -gunut- (May 8, 2006)

Given the same amount of powder in a casing how does felt recoil differ between low weight loads and heavy loads?


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## dladd (Sep 19, 2006)

I'm no ballistics expert but by thinking about the physics behind it, I'd say that with all things remaining constant and varying weight of the bullet will not affect recoil in any significant way. The initial inclination is to say that the recoil will be more with the heavier bullet because for every action there is an equal and opposite reaction. That means that to move a heavier slug, recoil will be increased. This isn't necessarily the case because there is another variable in play. On my Desert Eagle, it has 6" in which to accelerate the bullet. Holding the powder constant in the equation, the heavier bullet will not reach the same muzzle velocity as the lighter slug. So recoil will likely be the same. If you were to use a heavier slug and more/different powder in order to reach the same muzzle velocity, you would definately have more recoil. 

So to answer your question. I believe that recoil will be about the same regardless. Changing the slug and keeping all other factors constant, the recoil will not be more, but muzzle velocity will suffer.

That's my story and I'm sticking to it. 

dladd


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## -gunut- (May 8, 2006)

So do many .45 owners go for the lower weight rounds simply for more velocity?


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## dladd (Sep 19, 2006)

Well, that and the fact that a hollow point round will weigh less than a ball round. I personally shoot a lighter bullet because if someone is walking around in my house in the middle of the night, I want to make a big hole. The added velocity is just icing on the cake.

Again, I'm no ballistics expert and definately would like for someone who knows more than me about the subject to chime in but just because there is the "same amount of powder" in the case doesn't mean that all powders have the same burn characteristics. Some burn hotter and faster and therefore the same number of grains of one powder will more than make up for the increased slug weight yielding a round that is heavier AND produces more muzzle velocity.

Now you've exhausted my knowledge in both balistics and physics. :smt022 

dladd


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## Bob Wright (May 10, 2006)

Recoil is a function of action/reaction. The energy that drives the bullet is the same that drives the gun. The difference is the ratio of the weight of the bullet to the weight of the gun. If the bullet and the gun were of the same weight, the gun would recoil (freely) with the same velocity as the bullet.

Recoil is straight backward. The shape of the stock/grip affects muzzle rise. The closer the line of bore is to the hand, the less muzzle jump. This was the reason for the Russian "Hacksaw" framed target pistol of a few years back. Same goes for the "bullpup" design rifle stock, to minimize muzzle jump.

Venting the gasses has shown to have some effect on recoil reduction, such as the recoiless rifles of 75mm and 106mm used as atni-tank guns.

Bob Wright


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## Bob Wright (May 10, 2006)

Lightweight bullets can be driven to higher velocities, in the same gun/cartridge combination, while staying within reasonable chamber pressures.

For hunting or defense, bullet weight plays an important role. Lightweight bullets, with fast expansion, may not penetrate deeply enough to teach vital organs. I once talked with a man who had shot a 400 pound wild boar nine times with a .357 Magnum with little effect. The tusker was droppoed by a 12ga slug. The .357 bullets were 125gr. JHPs and went no deeper than the top fat layer. Because heavier bullets have more momentum, penetration is usually deeper. The greater the mass, the harder it is to get it into motion, and once in motion, harder to stop. Further, sectional density is of prime importance for penetration. A few years ago a famous archer demonstrated this by firing .30-06 into a bucket of sand. The sand stopped the bullet. He then shot an arrow through the bucket of sand.

Velocity is of importance for longer ranging shots, as there is less time for gravity and wind to effect the bullet's flight.

Weight also affects the pressure generated by the burning powder. Heavy bullets reach maximum chamber pressure at less velocity, while the lighter bullet reaches several hundred fps more before maxxing out.

Bob Wright


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## Wandering Man (Jul 9, 2006)

Wow, that's a truck load of information.

Bob, I always enjoy reading your posts.

WM


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## noproblem5671 (Dec 6, 2006)

*Hmm*

Bob, I'm a little surprised by your boar story. I read a study done for law enforcement agencies and it said the only round they tested that compared to .45 ACP in stopping power was .357 125gr JHP. ( Of couse they only tested rounds practical for LE. ) I guess the boar would have a lot tougher skin. It's a strange one. For defense the high velocity lower weight bullets seem to do better. MagSafe ammo which is used by some pretty heavy anti-crime units uses very light bullets with +P+ loads an expanding bullet with very high velocity. For law enforcement they require rounds that penetrate a minimum of 12 inches into 10% basistic gel. I guess the wild game just takes a lot more to stop than us humans. I knew a .357 was underpowered for boar hunting, but 9 shots with little effect is pretty remarkable.
When it comes to hunting the heavy bullets sure seam to have more stopping power from a handgun. Rifle rounds aren't that super heavy most of the time, but velocities are 2-3 times higher which lets them tear a good hole and still penetrate after expanding. Not much can compare to a 12 GA slug. I haven't had the pleasure of shooting such a load. I saw a test someone did to see how easy it is to shoot a padlock off like they do in the movies with a single handgun shot. The handgun shots never managed to take out the lock. Then they tried a 12 GA slug. It blew the lock to bits and they found pieces of the lock 50ft behind the target.


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## Snowman (Jan 2, 2007)

Bob Wright said:


> Lightweight bullets can be driven to higher velocities, in the same gun/cartridge combination, while staying within reasonable chamber pressures.
> 
> For hunting or defense, bullet weight plays an important role. Lightweight bullets, with fast expansion, may not penetrate deeply enough to teach vital organs. I once talked with a man who had shot a 400 pound wild boar nine times with a .357 Magnum with little effect. The tusker was droppoed by a 12ga slug. The .357 bullets were 125gr. JHPs and went no deeper than the top fat layer. Because heavier bullets have more momentum, penetration is usually deeper. The greater the mass, the harder it is to get it into motion, and once in motion, harder to stop. Further, sectional density is of prime importance for penetration. A few years ago a famous archer demonstrated this by firing .30-06 into a bucket of sand. The sand stopped the bullet. He then shot an arrow through the bucket of sand.
> 
> ...


This has really got me thinking. You bring up a good point about momentum, because such big deal is being made these days about energy. It seems that energy (1/2 * mass * velocity squared) is universally accepted as a measure of the bullet's destructive ability, while momentum (mass * velocity) is ignored. I looked into this a little further and found the following.

*Federal .357 JHP 125 gr (at muzzle)*
Energy = 576 ft-lbf ; Momentum = 25.7 lbm-ft/s
*
Federal .357 JHP 180 gr (muzzle)*
Energy = 466 ft-lbf ; Momentum = 27.7 lbm-ft/s

So while the lighter bullet has the advantage in energy, the momentum advantage goes to the heavier 180 gr. Does anyone else have any insight on why energy is used over momentum? I have a physics background but have a tough time translating it into anything practical :mrgreen:. It seems to me that, as Bob Wright eloquently put it, heavier bullets penetrate deeper because of momentum in spite of having less energy.

Thoughts?


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## noproblem5671 (Dec 6, 2006)

*A little hard to answer*

Your question is a little hard to answer. It has an impact, but felt recoil is hard to quantify. The best way to get an idea for yourself and see what diffence it makes to you would be to buy two boxes of the same brand ammo with different bullet wieghts. I'm not sure which ammo manufactures use the same or similar powder loads in their rounds, but I think you could get a pretty good idea.


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## noproblem5671 (Dec 6, 2006)

*Sweet*

Thanks Snowman. Bob gave us the the real world results perpective and you just gave us the science. I wish they did give the momentum numbers on the rounds in addition to the standard info.


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## Snowman (Jan 2, 2007)

No problem. I'm not good for much... :mrgreen:


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## Baldy (Jun 21, 2006)

Think I'll load me up some 125gr and 158gr in .357 cases with about 4.5grs of win-231 and see what they feel like. Do me a little test and see what they feel like.


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## Spenser (Nov 6, 2006)

To me, a 280 grain 45 kicks much harder than a 180 grain out of the same gun. It seems the physics support this.


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## -gunut- (May 8, 2006)

So what would make for a better defense round? Case and powder being the same; a 180gr HP or a 230gr HP?


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## 2400 (Feb 4, 2006)

noproblem5671 said:


> Bob, I'm a little surprised by your boar story....
> 
> I knew a .357 was underpowered for boar hunting, but 9 shots with little effect is pretty remarkable.


With different shot placement and bullet construction it might have been a different story.


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## Bob Wright (May 10, 2006)

Gentlemen, I can't seem to ever say anything simply.

As to penetration, the key, I believe, is sectional density, that is, the cross sectional area in relation to weight. Caliber remaining the same, the cross sectional density will increase with weight. This with an unexpanded bullet.

The light 125 gr. JHP .357 Magnum bullets are lightly constructed. As defensive bullets, they offer extreme stopping power when used against people. Unless something, heavy wool coat for example, opens up that bullet too soon. That is what happened in the case of the boar, the expanding bullet slowed and stopped before reaching vital organs.

Bullet selection and bullet placement are the all important criteria.

Bob Wright


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