Why exactly are wood stocks different than Carbon, chassis, etc.

[longrangelead]

Why exactly are wood stocks so "dead" feeling in recoil compared to carbon, aluminum, fiberglass and all the other man made stuff we've tried?

My hypothesis is the resonant frequency of wood is extremely low compared to the other materials.
Carbon and aluminum are dense and stiff, that's why we use them. I believe this is exactly why they have a higher resonant frequency that we feel during recoil, that "tuning fork" feel of a chassis for example.

I believe the much lower resonant frequency of wood has a damping effect on the steel part of the rifle, like touching a tuning fork to another object.
The wood absorbs the resonance of the metal.

I believe the opposite is true of carbon/aluminum for example. Carbon and aluminum seem to have resonant frequencies much closer to the barrel/action and do little or nothing to damp the resonance and we feel that in the stock or chassis.

From what I can find on googles, wood has a general resonance of 1.1 kHz. I'm sure that varies by species and density within a given species.
I can't find any solid resonance info on carbon fiber/aluminum/steel. The specific products we use in the gun industry may have specific resonance factors that have to be calculated anyway.

This could be a black hole of a rabbit trail. There are quite a few articles on sound absorption/reflection and musical qualities of wood...


I may have descriptive terms wrong but I think the idea is clear.

if some of you big brain engineers can fill this out with more technical information that would be cool to somewhat quantify the "why" behind the "feel".

@Tommyhaak

 

[Marbles]

Resonance is effected by length, is is why altering the length of 1 prong on a tunning form maks it no longer work correctly. Or, on 3 prong flash hiders making the prongs slightly different lengths fixes the tunning fork tone through electronic ear pro.

An interesting look an wood types effect on dampening in electric guitars. https://pmc.ncbi.nlm.nih.gov/articles/PMC8465587/

It sounds like solid carbon fiber guitar bodies are pretty similar to wood, but hollow not so much. Perhaps some of it has to do with having a shell and fill vs sold material more than a true difference in the material. If you hollowed out a wood stock and filled it with foam, I wonder how that would feel?

 

[longrangelead]

there is definitely a lot to it when you get down in the nitty gritty of specific shapes and combinations of materials.

Resonance is effected by length, is is why altering the length of 1 prong on a tunning form maks it no longer work correctly. Or, on 3 prong flash hiders making the prongs slightly different lengths fixes the tunning fork tone through electronic ear pro.

An interesting look an wood types effect on dampening in electric guitars. https://pmc.ncbi.nlm.nih.gov/articles/PMC8465587/

It sounds like solid carbon fiber guitar bodies are pretty similar to wood, but hollow not so much. Perhaps some of it has to do with having a shell and fill vs sold material more than a true difference in the material. If you hollowed out a wood stock and filled it with foam, I wonder how that would feel?

 

[BigNate]

There's a lot to consider here. The density is of course key. I wonder if there's a compressability factor, as wood is individual cells, arranged in linear fibers.

One thing I believe I've actually felt is certain synthetic stocks actually transfer less recoil, while the gun itself wasn't shooting as well. These were "identical" m24's, same ammo, same optics, both in synthetic stocks, one seemed to transfer more recoil but shot better groups.

 

[RockAndSage]

Great post. Something that came to mind would be to check if there's a difference between single-piece solid wood stocks, vs wood slabs laminated together, vs epoxy-filled laminate. I suspect @BigNate's point about compressibility is in play in how that frequency or the actual shockwave is transferred through the cells of the wood.

 

[longrangelead]

There's a lot to consider here. The density is of course key. I wonder if there's a compressability factor, as wood is individual cells, arranged in linear fibers.

One thing I believe I've actually felt is certain synthetic stocks actually transfer less recoil, while the gun itself wasn't shooting as well. These were "identical" m24's, same ammo, same optics, both in synthetic stocks, one seemed to transfer more recoil but shot better groups.

I believe compression or deflection is definitely present. A M70 for instance has to have a few thousandths clearance hehind the tang otherwise it chips the wood.
I don't know if it's overall compression, the thinner sides of the mag well deflecting, or both.

barrel resonance (harmonics) and effects of accuracy in individual rifles has been debated forever. there has to be something there in stocks too.

 

[Marbles]

I believe compression or deflection is definitely present. A M70 for instance has to have a few thousandths clearance hehind the tang otherwise it chips the wood.
I don't know if it's overall compression, the thinner sides of the mag well deflecting, or both.

barrel resonance (harmonics) and effects of accuracy in individual rifles has been debated forever. there has to be something there in stocks too.

Not a robust stock, but a bedded Kimber Montana stock needs clearance as well or it will chip the bedding. This was a 30-06.

 

[Colorado Cowboy]

I also think the type of bedding and material that was used has some effect.
If you have aluminum bedding I think it will stiffen up the wood. I also use JB Weld for bedding and it is really tough and can do the same as alum. Just depends on how thick it is.

The density on the type of wood (as mentioned) has an effect. I made a stock out of a type of tropical wood (I think it was cocabola) and it was so hard that it took 3 of 4 times as long to do the inletting.

 

[Kurts86]

There is a lot to this from a material science perspective.

Aluminum is an isoltropic material meaning it acts the same in every direction.

Wood and carbon fiber are anisotropic meaning they act differently in different directions. The difference is that with carbon fiber you can control each direction based upon the fiber orientation during layup. Wood is a function of grain direction.

Certain materials dampen vibration better than others, aluminum is really bad at dampening vibration, carbon fiber is better and wood would be best. If you’ve ever ridden a really stiff aluminum road bike you will be well aware of how much better carbon or steel dampen vibration. The same thing could be said hitting an aluminum baseball bat versus a wood bat.

Overall stiffness definitely is an overall factor, wood is going to deflect a lot more than carbon fiber or aluminum. Using a less stiff material will result in a long recoil impulse with a potentially lower peak velocity.

 

[DangerRanger]

Resonance is effected by length, is is why altering the length of 1 prong on a tunning form maks it no longer work correctly. Or, on 3 prong flash hiders making the prongs slightly different lengths fixes the tunning fork tone through electronic ear pro.

An interesting look an wood types effect on dampening in electric guitars. https://pmc.ncbi.nlm.nih.gov/articles/PMC8465587/

It sounds like solid carbon fiber guitar bodies are pretty similar to wood, but hollow not so much. Perhaps some of it has to do with having a shell and fill vs sold material more than a true difference in the material. If you hollowed out a wood stock and filled it with foam, I wonder how that would feel?

Oh god not the electric guitar body material rabbit hole.

The his is a hot ass topic in the guitar world

 

[Klooop]

There is a lot to this from a material science perspective.

Aluminum is an isoltropic material meaning it acts the same in every direction.

Wood and carbon fiber are anisotropic meaning they act differently in different directions. The difference is that with carbon fiber you can control each direction based upon the fiber orientation during layup. Wood is a function of grain direction.

Certain materials dampen vibration better than others, aluminum is really bad at dampening vibration, carbon fiber is better and wood would be best. If you’ve ever ridden a really stiff aluminum road bike you will be well aware of how much better carbon or steel dampen vibration. The same thing could be said hitting an aluminum baseball bat versus a wood bat.

Overall stiffness definitely is an overall factor, wood is going to deflect a lot more than carbon fiber or aluminum. Using a less stiff material will result in a long recoil impulse with a potentially lower peak velocity.

This. Large topic, really. Dynamics is a whole speciality career for some folks.

Materials:
- Isotropic (same properties in all directions like metals) vs anisotropic (properties depend on direction like composites and wood).
- Stiffness and damping. Two very different sets of material properties.
- Densities play into system mass.

Geometry:
- Plays into stiffness of structure.
- Plays into mass via amount of material.

Natural frequency (lowest resonant frequency, also has the largest amplitude) is essentially dictated by the relationship between stiffness and mass. This is normally the focus of these types of discussions, but harmonics follow a similar trend (integer multiples of the Fn).

Damping is basically material-induced losses that reduce the amplitude of the excitation/input and cause it to decay. If you are damping out the excitation input (acceleration), then you are also reducing its velocity at the same frequency.

So here we are talking about a few different characteristics together describing the vibration. We have the resulting structure natural frequency and then how quickly the input is damped out.

Isotropic materials are much easier to characterize without test than anisotropic materials. I think it is worth knowing about the difference between the two but wouldnt let that hold up any progress. Test is king anyways and used to ground analyses in this field.

 

[Klooop]

Great post. Something that came to mind would be to check if there's a difference between single-piece solid wood stocks, vs wood slabs laminated together, vs epoxy-filled laminate. I suspect @BigNate's point about compressibility is in play in how that frequency or the actual shockwave is transferred through the cells of the wood.

This is something I haven't really thought about, probably due to my lack of experience with laminated stocks....if the layers absorb some of the input.

Joints definitely result in losses for high frequency energy like you often see in a shock event. There's a possibility that maybe some of that occurs across the laminations as well. This would apply to both laminated wood and carbon. But laminated wood vs monolithic wood would at least be a closer comparison.

 

[nm.otter]

Dampening = wetting.
Damping = dissipating oscillations.

 

[Gstew1930]

i was pretty sure when i opened it, im certain now. im to dumb for this thread lol

 

[atmat]

Oh god not the electric guitar body material rabbit hole.

The his is a hot ass topic in the guitar world

Preach brother.

 

[Tommyhaak]

This is dissertation material here. To keep it simple, the three things that affect vibrations in a system are mass, damping, and stiffness. A light, stiff, minimally damped system ( carbon fiber ultralights) will be more problematic for vibrations than a heavier, lower stiffness, moderately damped system (wood, some laminates). Of course there’s shooter’s perception too, compared to measured data from an accelerometer.

Also wood looks better.

 

[Tommyhaak]

A Master Sporter IS the solution.

 

[longrangelead]

i was pretty sure when i opened it, im certain now. im to dumb for this thread lol

we'll bring you in on a cactus thread...

 

[Gstew1930]

Perfect. Im getting to be somewhat of an expert with plenty of first hand knowledge

 

[Wprinkle]

So on the topic of "dead recoil" of a wood stock vs a CF or "plastic"... Yesterday while shooting the trainer in a non wood rokstock, I had major vibration in the rifle. It was only 3 shots out of 80, I was prone shooting off of a flatbed truck, using front bag and rear bino harness, shooting mat. It sounded like a tuning fork in there and lasted 3-5 seconds... Any ideas what would cause this? I was shooting at 800 plus and did not notice any accuracy issues. Re checked the rifle at 200 ish yards and no vibrations and accuracy was fine. Rifle has 12000 ish rounds on it with no issues in the past.

Ideas?