Does Bore Size Affect Recoil?

6541 · Dec 16, 2014

Will two different bore sizes have approximately the same or appreciable different amounts of recoil for the same bullet weight traveling at the same velocity? Does different amounts of propellent to achieve the same velocity have an appreciable effect on recoil? Is recoil simply a function of bullet mass and velocity in rifles of the same weight?

I ask the question because it's a slow day and somewhere I read that the .270 Winchester has less recoil than a 30-06 Springfield for the same bullet weights and velocity.

It would seem to me that recoil is simply a function of bullet weight and velocity.

Leo · Dec 16, 2014

In physics they taught us "for every action there is an equal and opposite reaction". Your accessment is correct. The thing that is modified is the flavor of that opposite reaction (recoil) By changing the time duration, the directions of the reaction and the way the energy is used, we change the affect of the recoil on the shooter, but mathmatically, it is still the same amount of energy back as forward.

For example, in an inertia bolt semi automatic, a good amount of energy is used loading a spring for the reciprocating mass, so less recoil actually feels like it hits the shoulder.

PS, .270 winchester rifles feel like a lot less recoil because they are. A hunting bullet for a .270 is generally around 100 to 135 gr weight ( I have heard about 15o grain, but never shot any)and a 30-06 is 165 to 180 grain weights. I have never shot any .270 ammo that was the power of a 30-06. on the other side of the coin, I loaded up a lot of 125 grain varmint bullets in the 30-06 and they were really gentle on the shoulder.

zzt · Dec 16, 2014

Weight of the powder charge, weight of the gun and the velocity of the muzzle gasses are all factors in the formula for recoil. Bore size is not in the equation and does not affect recoil unless, all else being equal, it affects bullet velocity.

timb99 · Dec 16, 2014

As ZZT said, there are a lot of things that affect recoil. The stuff going out the muzzle is part of it, but you must include the weight of the burned powder in the formula. Different recoil formulas calculate that in different ways, but it cannot be ignored.

The weight of the gun you are holding plays a part in the recoil equation. The heavier the gun, the softer the recoil.

What you have probably read, and it is true, for the same rifle, with the same bullet, going the same muzzle velocity, there WILL be a difference if the case size of the cartridge requires more powder to get the same muzzle velocity. A .308 will have less recoil, all things equal, than a 300 Win Mag. Why? Because the case volume of the .300 Win Mag requires more powder to get the bullet up to the same speed as the .308. Therefore it will have more recoil.

Your example, a .270 vs. a .30-06' is a bit tenuous, as the cartridge case is nearly identical. It all depends on how much powder is required in the case to get the same bullet weight going the same velocity. If there is an appreciable difference, there may be a recoil difference.

221 · Dec 16, 2014

Where in physics is the weight of the powder a factor? Who's calculation made the determination that it has an affect? Specifically, what does the powder weight have to do with recoil? I think you'll find the powder weight really is an algorithm to make up for the inability to measure the rate the pressure rises. It's a burn rate multiplier.....YES....NO?

It's the acceleration of the projectile, not the velocity. Physics has always been Acceleration. Gun writers have concluded it's Velocity. Velocity is only a measurement of speed at a particular point. Whatever energy that is transferred to a firearm happens long before it gets to the chronograph. When someone develops 10 different loads that all read 1200 fps @ +3ft, they have 10 different loads and all things are no longer equal. There is no way to claim those 10 loads all have the same acceleration rate.

Recoil is what the firearm transfers to the shooter. Energy is not transferred to the firearm because of velocity. These nay sayers will use the reasoning that a person can not sense differences in recoil, due to the speed, energy is transferred to the gun. It's immaterial how fast energy transfers to the gun. How the gun transfers it to you, is.

Oregunner · Dec 16, 2014

Good recoil calculator. http://www.omahamarian.org/trap/shotshellenergy.html
Includes an explanation at the bottom.

221 · Dec 16, 2014

It's an estimation.

Before you shoot a shotgun the gun and the shot shell pellets are both at rest. After you shoot the pellets/wad/powder goes out the barrel and the gun goes in the other direction. The key here is momentum which is mass times velocity.

The recoil would be the mass of the gun and the velocity it's moving. That is what we feel,IE recoil. The projectile's mass and velocity is what the target feels. The momentum of the firearm is not caused by the momentum of the projectile. If it were we would never be able to shoulder a firearm.

In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object.

6541 · Dec 16, 2014

Thanks for all of your responses.

A long ago article that bounces around in my head contained a theory that the larger the bore, the greater the surface area at the breach. The recoil forces would have some type of mechanical advantage by being able to apply pressure to a larger area. The reasoning was that the smaller the bore, the less force was applied to the gun and thus less recoil for the same weight and velocity of bullet. Does this ring any bells in anybody's mind or was this just junk?

timb99 · Dec 16, 2014

6541 · Dec 17, 2014

Yes, junk, end of story. Again, thanks for all of your replies and excellent information.

Leo · Dec 17, 2014

Surface area has nothing to do with total recoil. Think of this: You drop a 4 lb hammer on a 1/2" steel rod. Now drop a 4 lb hammer on a 6 X 6" fence post that weighs the same as the steel rod. It is the same total energy transfered. The fact that the concentration of the energy in the example on a small area can split a brick and that same energy on the post does not split a brick, does not mean the energy transfer is less, it is just presented to the brick in a different form.

That is one of the reason the buttstocks on a trap gun get bigger back to a pad that pretty much fills a 2" X 6" rectangle. A 1" diameter hickory dowel rod is plenty strong enough to mechanically do the job of holding the shotgun forward in the right place to shoot. I'll bet no one would like to shoot it.

Leo · Dec 17, 2014

Teacher, did I prove that I paid attention in Physics?

I have an off topic story that I think is funny. I participate on another firearms site also. There was someone that was asking a lot of questions that were developing into a structured pattern. I did my Masters work in Psych, and am still working on my Phd. as health and finances allow. The person asking the questions was working on his project for a paper. I worked on a project with the same formula my first year of Psych. I contacted him in private emails. We were his control group.

Shooting Coach · Dec 17, 2014

You guys are nuts!

My 12 kicks a lot more than the 410. Any questions?

Avaldes · Dec 17, 2014

Accelerating the shot from rest to muzzle speed requires force...that force is reacted by your shoulder. If one configuration versus another has more or less recoil, you can pretty well bet that the speed of the shot has been changed.

Peter Sinclare · Dec 17, 2014

Recoil is directly affected by:
1) The weight of the projectile. 2) Velocity. 3) Weight of the gun.

But how you feel about (the perceived recoil) might be different.

jim brown · Dec 17, 2014

Perceived recoil should be renamed Voodoo recoil.

Perazzi_MX8 · Dec 17, 2014

wolfram · Dec 17, 2014

Yes and no on the surface area of the base of the bullet. In the .270 Vs 30-06 comparison, the .270 will only get around 2,750 fps at the muzzle with most 150 grain bullets whereas you can expect 3,000 or so from a 30-06 loaded to similar pressure levels. The greater velocity occurs from pressure of the propellant being applied to the larger area associated with the .30 cal projectile. You also get more recoil from the .30 cal rifle in this case because of the greater velocity. But if you were to reduced the charge in the 30-06 150 grain load to match the vel from the .270 , 150 grain load then recoil level would also be the same.

Also the heavy for caliber projectiles like the 150 and 170 grain .277" bullets are fairly long and occupy some of the internal case volume when seated deeply enough to function in standard length magazines and normal barrel throats. By contrast the 150 grain .30 cal projectiles are kind of stubby and really don't get into the internal case volume at all and this allows the cartridge to be safely loaded with more propellant which equates to more velocity.

Perazzi_MX8 · Dec 18, 2014

wolfram said:
Yes and no on the surface area of the base of the bullet. In the .270 Vs 30-06 comparison, the .270 will only get around 2,750 fps at the muzzle with most 150 grain bullets whereas you can expect 3,000 or so from a 30-06 loaded to similar pressure levels. The greater velocity occurs from pressure of the propellant being applied to the larger area associated with the .30 cal projectile. You also get more recoil from the .30 cal rifle in this case because of the greater velocity. But if you were to reduced the charge in the 30-06 150 grain load to match the vel from the .270 , 150 grain load then recoil level would also be the same.

Also the heavy for caliber projectiles like the 150 and 170 grain .277" bullets are fairly long and occupy some of the internal case volume when seated deeply enough to function in standard length magazines and normal barrel throats. By contrast the 150 grain .30 cal projectiles are kind of stubby and really don't get into the internal case volume at all and this allows the cartridge to be safely loaded with more propellant which equates to more velocity.

Really? What mathematical formula are you using? The cases are identical from the shoulder back with the only difference of .031" diameter at the neck along with the .270 case being longer. The head-space gauges are one in the same for the .270 Winchester and .30-06 Springfield. The only conceivable difference would be the bearing surface on the full diameter of the 150 gr. bullets and boat-tail bullets change that. I have owned a chronograph for 40 years and have no problem reaching 3000 FPS in either caliber with 150 gr. bullets out of identical (Pre-64) M70's with 24" barrels.

I know this is a theoretical question but you managed to peg the BS meter. I'd like to think that your at least willing to share what your smoking!

wolfram · Dec 18, 2014

1/2MV^2 comes to mind and I did mention V didn't I?

Please share some reliable loading data that gets 3,000 fps from a .270 Winchester and 150 grain bullets. Better yet how about the data for common factory loaded .270 150 grain ammunition. Gotta warn you on this - I have been working on .270 load development recently so the results are current in my mind ....

Does Bore Size Affect Recoil?

6541

Leo

zzt

timb99

221

Oregunner

221

6541

timb99

6541

Leo

Leo

Shooting Coach

Avaldes

Peter Sinclare

jim brown

Perazzi_MX8

wolfram

Perazzi_MX8

wolfram

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