May be the wrong forum but I am asking about factory ammo.

I would like to know if a 12 ga. load and a 20 ga. load of the same ounces of shot (say 7/8 oz), the same velocity ( say 1200 fps) and the same shot size (say #9) with the gun weights, stock fit, chokes, recoil pad, etc. exactly the same, will have the same recoil?

12 will have less recoil everything else being equal.
bernoulli formula

Thanks pullit. I thought so but I had no idea why. I just looked at the formula and it is way over my head but you confirmed my instinct/guess on this.

By how much?

I really don't think you could tell the difference.

Why is the 12 less if it is loaded with more powder than the smaller shell of the 20?

I shoot 7/8 12 gauge loads exclusively in my Beretta 680 series for sporting and trap. I was loading and shooting 7/8 oz loads in my 20 gauge guns yet dropped down to 3/4 oz loads for skeet and occasional sporting clays due to recoil. Of course my 20 gage guns are lighter by a pound of gun weight so I'd say recoil is the same with gun weight being equal.

****my reason for shooting 3/4 oz loads in the 20 gauge is you don't or I don't need more than 3/4 oz loads to break a skeet bird. A alternative to a 28 gauge.

Or is both shells the 12 and the 20 loaded with equal amounts of powder if both 1200 fps velocity?

Or is both shells the 12 and the 20 loaded with equal amounts of powder if both 1200 fps velocity?

And do the wads weigh the same?

The 12 ga would have more recoil due to more ejecta (powder and wad weight) but the difference would be minuscule and unnoticed by the shooter. The difference in pressure has no affect on the amount of recoil but it might, I repeat might, result in a difference in recoil speed but that is as much theory as reality per the arguments that have been twirling around for a century or more.

I can tell you that stock fit play way more into felt recoil than most people give it credit for.

What Pullit said. Started shooting 7/8 loads in the 12s long time back. Fully functional and difference in recoil between the 12 & 20 is insignificant.

So true. So freaking true. and it took me WAY too long to accept this fact. I knew it, jsut not HOW much it mattered. Plus, I was stubbord, pigheaded, and poor.

Newton knew. Equal and opposite reaction and all that. Push the same total weight out the front of the muzzle at the same velocity (including weight of power and wad) = same amount of energy being directed in the opposite direction. Guns of the same weight will have the same inertia and therefore the same actual recoil. Stock shape may affect "felt" recoil, but real recoil energy would be almost the same (imperceptible difference to a human). The size of the hole would make no difference. (I'm just referring to shotguns when I say that.)

That's also my reason for shooting 3/4 oz loads in my 12 gauge for Skeet.

Burning rate of powders also can come into play as far as felt recoil, a slower powder can spread the recoil impulse over a longer period of time. Same recoil, many of us with old shotguns load low pressure(same velocity) with slower powders to save 100+year old wood stocks.

There will be subjective results stated here that are all over the map.

Recoil is strictly a function of mass and velocity. The subject has been beaten to death on shotgun forums but the facts have not changed.

Short answer, yes they will be the same. Recoil is kinetic energy. There are formulas to calculate this, but converting to foot pounds of felt recoil is too easily fudged by gun weight, shooter impressions, barrel length, etc. etc.

Autoloaders seem to recoil less because they spread it out over time.

HM