Rifles: perceived recoil vs true recoil?

[Ds J]

Just out of interest, on a sideline to the last pages of this thread:

Is there something like perceived recoil vs true recoil in rifles? It is true for handguns, but how does it work in rifles?

I know that the design of the stock plays a role. What else?

[Desperatezulu]

Recoil impulse - how quickly the gun recoils.
Different powders (even with similar muzzle velocities) have different pressure curves/peaks which affect felt/perceived recoil.

[Messor]

Recoil Energy
The energy of the recoiling firearm under free recoil
Recoil Impulse
The momentum of the recoiling firearm under free recoil
Recoil Velocity
The velocity of the recoiling firearm under free recoil

Your perceived aspect falls mostly within the last 2.
Although it's basically impossible to compare from human to human, humans differ, one it hurts the other it does not.

[gary-t]

Just out of interest, on a sideline to the last pages of this thread:

Is there something like perceived recoil vs true recoil in rifles? It is true for handguns, but how does it work in rifles?

I know that the design of the stock plays a role. What else?

Stock fit plays a big part in felt recoil. A badly fitting or designed stock can make recoil feel much worse.

[janfred]

Just out of interest, on a sideline to the last pages of this thread:

Is there something like perceived recoil vs true recoil in rifles? It is true for handguns, but how does it work in rifles?

I know that the design of the stock plays a role. What else?

Yes.

Recoil is caused by the bullet being violently shoved out the barrel in one direction by lots of hot gasses. Similarly, the rifle is shoved violently the other way by the bullet and gasses. You are on the butt end arresting yhe rifle and experience this as recoil. Messor summarised it well.

One way of reducing the perceived recoil is to drop the butt below the bore line. In this way, some of the recoil energy is used to lift and rotate the rifle upwards reducing the amount you feel in your shoulder.

Another way is to use a heavier rifle. This reduces the recoil velocity. The momentum is the same, but the "sharp kick" turns into a more "gentle shove".

One way to reduce the actual recoil is to fit a muzzle brake. As recoil is a combination of the bullet's acceleration in the barrel and the velocity of the gas exiting the muzzle, the muzzle brake redirects a major portion of the muzzle blast sideways and slightly rearwards, there by reducing the muzzle blast effect on recoil.

Another way is to use a silencer. This reduces the velocity that the gas exits the muzzle.

[Ds J]

With pistols, a heavier bullet causes slower movement of the slide. It has more energy but moves slower. Thus, the recoil feels less snappy.

With rifles, it comes down to a "shove" instead of a "kick"?

To take from Messor's explanation:

Less energy can be transferred faster and harder, or more energy can be transferred slower and softer?

[414gates]

There is produced recoil, and felt recoil.

Recoil is produced by the amount of gas exiting the muzzle.

When you use more of a slower powder, you produce more recoil than when using less of a faster powder.

Felt recoil is reduced by the rifle weight, or by diverting the gas before it exits the muzzle, with either a suppressor or a brake.

[Messor]

With pistols, a heavier bullet causes slower movement of the slide. It has more energy but moves slower. Thus, the recoil feels less snappy.

With rifles, it comes down to a "shove" instead of a "kick"?

To take from Messor's explanation:

Less energy can be transferred faster and harder, or more energy can be transferred slower and softer?

Uhm – No

A lot of it will come down to efficiency, the more efficient the combo the less recoil there will be.
When you up the charge to obtain a certain speed, for example if you try and shoot a 165gr bullet from a 30-06 at the same speed as a 308, then all 3 factors increase.
Recoil energy, recoil velocity and recoil impulse increases, and that is simply because the 308 is more efficient, that is why I’ve always said don’t buy a 30-06 when you want to shoot it at 308 spec, which in reality plenty people do.

It is important to note you CANNOT change these values, all you can do is mitigate them, sure you can add weight to the rifle and add a muzzle break but that is not changing the mathematical equation.
I’ll add the mathematical equation below for those that can follow the maths.
If you add a decelerator pad you change how fast the rifle hits your shoulder, now it will feel more like a shove than a kick, also why some of the old 303 rifles kicked people so hard, no deceleration into the shoulder.
Or how you sit, if you sit upright with a big rifle the recoil is far better than if you lean into the rifle on a bench, or worse prone, again, your body cannot move back fast enough to reduce impact.
Or how you redirect the gasses, muzzle brake etc.

It comes down to this, example, I want to shoot a 180gr bullet at 2400f/s to do my bushveld hunting.
Now you go and do research into what cartridge will do that for you most efficiently with the rifles and powders avail to you.


https://saami.org/wp-content/uploads...018-07-9-1.pdf

[A-R]

With pistols, a heavier bullet causes slower movement of the slide. It has more energy but moves slower. Thus, the recoil feels less snappy.

With rifles, it comes down to a "shove" instead of a "kick"?

To take from Messor's explanation:

Less energy can be transferred faster and harder, or more energy can be transferred slower and softer?

The pistol explanation is unsatisfactory. Pistols are usually loaded to a certain "factor" meaning a certain level of momentum. The minimum is usually what is needed to cycle reliably, or what the rules of a certain game allow. Them max load in a pistol is usually determined by 2 things: 1. Max allowable pressure and 2. Max allowable slide velocity. We are talking about initial velocity here, as as soon as it moves, the RSA is starting to slow it down. If it goes too fast, it will batter the pistol to bits, sooner or later. Newton devised (observed actually) a law, saying that momentum is never lost, only transferred. (Energy is likewise converted from one form to another.) So the sum total momentum of the forward moving parts must equal the sum total of reward moving momentum. Forward = bullet and escaping powder gas. Rearward = Slide, frame and anything else attached to it, like hands and shoulders. So a fast, light bullet and slow heavy bullet should deliver the same recoil momentum if loaded to the same "factor". The only variable is the powder weight, but that is very small. So the recoil should be the same. What does differ is the time span of the transfer of momentum from pistol to shooter (impulse). Even a very small difference in the transfer time, causes a difference in the impulse or perceived recoil. To take a better example: A 357 Mag revolver shooting a 158gn bullet at 1350fps has a significant "bite" to it, while the same revolver shooting a 220gn bullet at 970fps has much more of a "push" to it. Similar momentum, very different feel. Granted, the solid frame of the revolver transfers the recoil directly to the shooter's grip. On a pistol, the moving slide and RSA interrupt the transfer and spread it out much more evenly.

Now to rifles. The same principles apply here, but due to the nature of the setup, there are different factors at play too.
The most important factor is the shape of the comb on the stock. A straight comb, as high as possible, gives the least upward "whack" to your face, hence gives the best recoil control. The recoil goes straight back and does not hit you in the face. I am always amazed by how many people seem to be happy with these ugly Bavarian humpback stocks on their big bore rifles. I would not even want to use that on a 308.
Another significant factor in a big bore rifle is the powder burn rate. If you use the same bullet at the same MV, but one is pushed by a load of fast-burning powder (e.g. S335) and another is loaded with slower-burning (S365), the fast-powder load will have significantly more "bite" to the recoil while the slower one will feel more like a "push". With rifles, the portion of recoil added due to expelled powder gasses is significant, so the greater volume of slow powder will actually result in more raw recoil. However, this will be spread out over a longer time period, resulting in a softer recoil impulse and less perceived recoil. This was the primary driving factor behind the development of the 458 3" Exp cartridge, more space, slower powder, less bite. And I have shot Prof Koos Badenhorst's 458 3" Exp off a bench, sitting...
The other factors that affect recoil are off course rifle weight, bullet and powder weight, stock material (these modern cheap moulded plastic stocks flex quite a bit and absorb a lot of recoil), recoil pad design and material (The Sorbathane and similar soft materials make a huge difference.), the addition of recoil-dampening devices (mercury tubes etc.) and off course muzzle brakes (not breaks, we don't want it broken). A suppressor acts as a brake, as it slows the forward velocity of the powder gasses. If it changes their direction on exit, even better. (Just a pet peeve about those who advertise their suppressors with internal brakes: Since it does not change the final direction of the gas, it has zero effect on recoil. A brake needs to be open to work.)
I might have missed a few. For example, just the other day I held a very pretty rifle in a very potent DG caliber. It was a sight to behold with all the engraving and detail that went into it. I was also offered a few rounds to shoot, but I declined. You see, the pistol grip was shaped in a manner that brought the knuckle of my middle finger very close to the engraved (cheese grater) trigger guard. On recoil, that thing would really smack my knuckle. No thanks! Have a look at the stock shapes of the A-Square rifles designed by Art Alphin. They all have a generous gap between the pistol grip and the trigger guard. It is there for a reason. The rest of the features on his stocks were also all designed to mitigate recoil and promote shooter comfort.

So, look at the whole picture and all the various features. Every one contributes to the perceived recoil to some extent.

[Ds J]

Thanks Folks! It clears things up.