Harmonics and F-Open stock

[CharlieNC]

Not to be nit picky, but there are differences between barrel harmonics and "vibration". In his book Vaughn shows a major reduction in barrel vibration, or probably better expressed as a short term cycle of major amplitude, with modifications to the recoil lug area to absorb energy from the shot impulse. On the other hand barrel harmonics are longer enduring cycles of numerous frequencies with much lower amplitude, as the barrel is free floated as a cantilevered beam; I don't forsee the stock material would influence this if properly bedded.

 

[gunsandgunsmithing]

Not to be nit picky, but there are differences between barrel harmonics and "vibration". In his book Vaughn shows a major reduction in barrel vibration, or probably better expressed as a short term cycle of major amplitude, with modifications to the recoil lug area to absorb energy from the shot impulse. On the other hand barrel harmonics are longer enduring cycles of numerous frequencies with much lower amplitude, as the barrel is free floated as a cantilevered beam; I don't forsee the stock material would influence this if properly bedded.

I'm not sure what your question or statement is. I look at it that everything, from the top of the gun down to the rest feet can have some influence on the end result. Isn't a super hard front bag a factor, for example? How about how tight the gun is in the front rest and how does that affect break away of the stock in the bag. I've seen a really tight front bag actually cause a gun to twist and jump because it couldn't break away freely. That energy has got to come out somewhere. Just another example..one that might seem counterintuitive but happens.

 

[CharlieNC]

I'm not sure what your question or statement is. I look at it that everything, from the top of the gun down to the rest feet can have some influence on the end result. Isn't a super hard front bag a factor, for example? How about how tight the gun is in the front rest and how does that affect break away of the stock in the bag. I've seen a really tight front bag actually cause a gun to twist and jump because it couldn't break away freely. That energy has got to come out somewhere. Just another example..one that might seem counterintuitive but happens.

Yes I agree all those factors matter. To me harmonics imply the barrel vibrating like a tuning fork, with somewhat characteristic frequencies and amplitudes, which we can utilize for tuning loads. Other factors you mentioned are more like a sucker punch, disruptive, which must be dissipated and addressed as a problem; not useful for tuning.

 

[Twdmar]

A laminated wood stock would be a more stable, and possibly more vibrational absorbent depending on the materials used. With a plywood type laminate, the perpendicular arrangement of the layers probably makes a difference.
. There are some composite fabrics that claim to have vibration reducing properties and research shows certain composites based on their structure are better at it, i.e. chopped fiber composites.
Will it work of one of those composites is laminated with wood, who knows. Fiberglass will move some, look close next time you see an old corvette. For my shooting, I doubt wood vs fiberglass matters.
If you look at the experience of some of the posters who've messed with stocks and tuning them, I would say their input has a great deal of value, especially in relation some factors like aluminum or glued in actions. There is enough evidence from them for it to not just be anecdotal.
If you're a cabinet maker you'll have no issue making a stock, so do it and see. Baltic birch ply with nice wood on the sides is probably adequate. Inlet some of those little rubber dampeners Matthews bows put in the limbs of their compound bows. I think you could put them under the barrel channel even. If it's crap, buy the fiberglass.

 

[gunsandgunsmithing]

Yes I agree all those factors matter. To me harmonics imply the barrel vibrating like a tuning fork, with somewhat characteristic frequencies and amplitudes, which we can utilize for tuning loads. Other factors you mentioned are more like a sucker punch, disruptive, which must be dissipated and addressed as a problem; not useful for tuning.

I can't really agree because of one scenario that I gave you. Say the gun is held too tightly in the front rest. That energy has to come out somewhere. If nowhere else, it will increase the amplitude of bbl vibration. Same goes for shooting significantly uphill, where the gun can nearly slide off of the bench. Try this sometime...shoot your rifle over a chrono both pinned hard against the stop and totally free recoil. Pinned hard will shoot a little faster. That's directly related to tune, my friend.

 

[Twdmar]

I know a lot us like audio equipment, usually it’s the guys that double up on the hearing protection with plugs inserted so deep they need a key to remove, because these two interests are at odds with each other.

Nothing wants to set itself into harmonic resonance more than a loud speaker. The goal of a good enclosure is to avoid coloring the sound of the transducers with its own tendency to start ringing.

On purely that captioned question of harmonic dampening, braced or thick wood or wood products such as MDF, is just about universally accepted as the best material to dampen vibrations across the entire spectrum of frequencies.

That’s not the only priority for a stock, as I reflect on the worst downpours ever in Ottawa in 2017, but I think among the other stock options of composites and metals, thick wood dampens vibrations better and is inherently nonuniform across its length so as to resist harmonic resonance as well.

This is an interesting perspective. It also makes me wonder how a stock with carpet attached to the outside would work. While that sounds silly, bundles of yarn attached to bowstrings are pretty good at absorbing vibration.
The random orientation of MDF probably plays a factor just like steel and aluminum transmitting vibration is not good because of the structure of metals.

 

[Twdmar]

I can't really agree because of one scenario that I gave you. Say the gun is held too tightly in the front rest. That energy has to come out somewhere. If nowhere else, it will increase the amplitude of bbl vibration. Same goes for shooting significantly uphill, where the gun can nearly slide off of the bench. Try this sometime...shoot your rifle over a chrono both pinned hard against the stop and totally free recoil. Pinned hard will shoot a little faster. That's directly related to tune, my friend.

Can you clarify what you mean by tune in the sentence about the it being the reason for greater speed?

 

[gunsandgunsmithing]

Can you clarify what you mean by tune in the sentence about the it being the reason for greater speed?

It'll physically shoot faster when pinned hard than when totally free to recoil. That simple. Typically 8-15 fps but variables like gun weight and total recoil are variables. Bottom line, energy is not spent pushing the gun backward when pinned hard.

 

[Twdmar]

It'll physically shoot faster when pinned hard than when totally free to recoil. That simple. Typically 8-15 fps but variables like gun weight and total recoil are variables. Bottom line, energy is not spent pushing the gun backward when pinned hard.

Ok, that is what I was thinking. I just never heard of it referred to as tune. I was thinking about physics class from forever ago.

 

[gunsandgunsmithing]

Ok, that is what I was thinking. I just never heard of it referred to as tune. I was thinking about physics class from forever ago.

Lol! I think it is physics, just probably more simple that you were thinking. Faster bullet exits sooner, right? So, the bbl hasn't had time to come to its optimal position, right? To me, that's tune.

 

[Twdmar]

Lol! I think it is physics, just probably more simple that you were thinking. Faster bullet exits sooner, right? So, the bbl hasn't had time to come to its optimal position, right? To me, that's tune.

Ok, I see. A lot of people use the word tune and it seems to encompass a lot of different definitions.

 

[gunsandgunsmithing]

Ok, I see. A lot of people use the word tune and it seems to encompass a lot of different definitions.

I agree. I believe there are powder tunes and vibrational tunes. Powder can have velocity plateaus but steel is gonna vibrate pretty much the same over a very wide temp swing...much more so than powder burning. I cringe when I read or hear people talking about a tuner setting that has width. It just doesn't compute. Each mark on a tuner has a value relative to tune. Not necessarily so with powder charge, if you are at a velocity plateau. IOW, there is no spot on a tuner that should be several marks wide. I want it to matter, with every adjustment. I know there have been some people that will disagree with this but I've never read or heard anyone explain why they think it does. OTOH, I can explain why it does not and why powder charge does. It's just two different things. I think people that struggle with a tuner are often looking for that spot when it SHOULDN'T BE THERE. That's powder tuning..not tuning to a constant vibration. Again, two different things that have to be tuned for separately. Moving a tuner is essentially changing a constant. No need to split that hair too many ways when it's semantics that temp changes frequency. Yes, but again, semantics...forget about it.

 

[Fuj]

I use aluminum chassis exclusively. 3 big factors......Do you sling/
freehand ??.....Shoot from a bipod ??..... Or fully rested in sand bags
fore and aft ?? I use MDT aluminum chassis as a platform for my
builds. I do a 3" wide fore end that gets laid upon a soft sand bag
on a 31 lb rest. Butt stocks are 1.25" wide and flat, and nested into
a heavy sand Bumble Bee bag. I shoot unlimited where my 2 rifles
very from 17lbs to 21lbs. So, you have to consider all the aspects
before dishing on an aluminum stock. I've posted this before, so for
anyone that has not seen it, this is what I do for aluminum stock
fore ends......

Funky bench just used for dog and pony pic.