Optimal Barrel Time?

[.300winmag]

What I want to know is how OBT takes into account the different contours of the barrel, along with different calibers (bore diameters). Both of these variables will affect the moments of inertia (rigidity) of a barrel. Fluting will also affect this. All of these factors also affect the natural frequencies of the barrel as does material. I just glanced over the article, I will have to sit down and really read through it. But, just by glancing through it, all I saw charts for were different barrel lengths. I think there is a lot more to this than what the author investigated, and is a lot more complex. Still interesting and I think there may be some useful information to it. I have just never used OBT in load development.

 

[SJB358]

What I want to know is how OBT takes into account the different contours of the barrel, along with different calibers (bore diameters). Both of these variables will affect the moments of inertia (rigidity) of a barrel. Fluting will also affect this. All of these factors also affect the natural frequencies of the barrel as does material. I just glanced over the article, I will have to sit down and really read through it. But, just by glancing through it, all I saw charts for were different barrel lengths. I think there is a lot more to this than what the author investigated, and is a lot more complex. Still interesting and I think there may be some useful information to it. I have just never used OBT in load development.

I was hoping you would chime in buddy. As the driver of some incredible shooting rifles, I knew you'd have some perspective on it.

I thought the same thing, how does barrel thickness change it, along with rigidity?

I am assuming it still moves, but less than a small diameter barrel, but the waves are the same, just smaller?

I'd love to know more.

 

[Ridgerunner665]

I am assuming it still moves, but less than a small diameter barrel, but the waves are the same, just smaller?

You assume correctly...larger contour, more rigid, less flex...the waves move at nearly the exact same rate, but the stiffer barrel doesn't flex as much...in any direction.

This has a lot more to do with "time" than contour...

 

[SJB358]

I am assuming it still moves, but less than a small diameter barrel, but the waves are the same, just smaller?

You assume correctly...larger contour, more rigid, less flex...the waves move at nearly the exact same rate, but the stiffer barrel doesn't flex as much...in any direction.

This has a lot more to do with "time" than contour...

Whats that old saying, "sunlight shines on an old dogs butt once in awhile" :lol:

 

[Ridgerunner665]

LOL...lots of those sayings...using everything from blind squirrels to old dogs, lol.


When you think about it...I doubt this is anything any of us didn't already know (stiffer barrels are more forgiving)...but maybe just a better understanding of what we have known all this time.

Now we not only know that stiffer barrels are more forgiving...we also understand why.....knowledge is power!


Barrel material...that is one variable that I believe does make a difference, but I'm not sure its enough to be of any consequence, and is, I believe, one of the reasons for the 2-3% margin of error...along with the condition of the rifling (rough, smooth, lapped, Remington :mrgreen: )

 

[SJB358]

Yup, great point. I know it isn't exact but it lines up very closely to almost all my accurate loads. Can't say it's completely right but I'd be darned if I could prove it entirely wrong either.

 

[Oldtrader3]

What I want to know is how OBT takes into account the different contours of the barrel, along with different calibers (bore diameters). Both of these variables will affect the moments of inertia (rigidity) of a barrel. Fluting will also affect this. All of these factors also affect the natural frequencies of the barrel as does material. I just glanced over the article, I will have to sit down and really read through it. But, just by glancing through it, all I saw charts for were different barrel lengths. I think there is a lot more to this than what the author investigated, and is a lot more complex. Still interesting and I think there may be some useful information to it. I have just never used OBT in load development.

I agree, I think trying to calculate it is a pretty empirical exercise that could drive one crazy. Like a lot of other engineering exercises (i.e. calculating pipe flow with Reynolds numbers), it gets you in the ball park but does not get you dead nuts without a lot of experimentation. Hence the idea of the BOSS mechanism which allows correction for variables.

As you mentioned, fluting and ribs etc. change the Moment of Inertia calculation. I am too old now to be empirically inclined.

 

[.300winmag]

What I want to know is how OBT takes into account the different contours of the barrel, along with different calibers (bore diameters). Both of these variables will affect the moments of inertia (rigidity) of a barrel. Fluting will also affect this. All of these factors also affect the natural frequencies of the barrel as does material. I just glanced over the article, I will have to sit down and really read through it. But, just by glancing through it, all I saw charts for were different barrel lengths. I think there is a lot more to this than what the author investigated, and is a lot more complex. Still interesting and I think there may be some useful information to it. I have just never used OBT in load development.

I agree, I think trying to calculate it is a pretty empirical exercise that could drive one crazy. Like a lot of other engineering exercises (i.e. calculating pipe flow with Reynolds numbers), it gets you in the ball park but does not get you dead nuts without a lot of experimentation. Hence the idea of the BOSS mechanism which allows correction for variables.

As you mentioned, fluting and ribs etc. change the Moment of Inertia calculation. I am too old now to be empirically inclined.

Reynolds number is a great example...hell, most textbooks vary on what the reynolds number threshold is. It'd be a huge under taking to do this, one I would like to see someone pursue. It'd be about a lifetime of work though, but, as technology improves, this will become easier to study.

Very interesting to think about! Great thread

 

[wildgene]

...good info, but I wouldn't get too wound up over it, it's still one of demdere "Best Guesstimate" numbers. The better the numbers, the better the "guesstimate", but barrels are different. Just like BC's & max loads, it's still an estimate of what should happen, a very good reference point, but w/ the variables involved, I wouldn't consider it "set in stone"...

 

[Ridgerunner665]

No...it's not set in stone...but it can save a person some rounds fired...I love to shoot, but at today's prices of guns, ammo, components, and barrels....I'm leaning heavily towards becoming one of those guys that doesn't fire more than 25 rounds per year from a hunting rifle...and use a plinker (22) to keep my trigger finger in shape, and even that is getting expensive.

I truly enjoy extensive load work ups...but any more I see it as a bit of a waste...I'd rather get there the quickest way possible, then haul my rifle to ORSA (75 miles) and verify my drops on their 1,000 yard range (twice, different days, plot temp changes)....and call it good, with less than 100 rounds fired....the rifle will then be sighted in, broken in, and sufficiently coppered to remain stable for a season or two.

 

[Dwh7271]

RR, I agree. Excellent points.
The flex (or movement)of the steel would obviously change w barrel size, contour or flutes as others pointed out but the speed of the harmonic through the steel should remain a constant, right? The reactions from that harmonic would then vary based on barrel length, I believe.
FWIW, it seems a viable alternative to a ladder test or other similar options, though I'm certainly not putting any of those down
In the end, I guess whatever works for you is fine.
I just brought it up because it fascinated me.

 

[Ridgerunner665]

You got it...

 

[.300winmag]

RR, I agree. Excellent points.
The flex (or movement)of the steel would obviously change w barrel size, contour or flutes as others pointed out but the speed of the harmonic through the steel should remain a constant, right? The reactions from that harmonic would then vary based on barrel length, I believe.
FWIW, it seems a viable alternative to a ladder test or other similar options, though I'm certainly not putting any of those down
In the end, I guess whatever works for you is fine.
I just brought it up because it fascinated me.

The harmonics through the steel would change based on the composition of the steel. For example, they will vary from stainless to blued steel, simply because of the microstructure of the steel. Then, even 416 stainless varies from lot to lot. I would say all of these variables are minor, but the goal is to make as accurate model as possible. You would have to definitively prove the difference between stainless and blued steel is negligible or develop models for each type. I doubt you would see any measurable difference, however.

The more I think about this thread the more I want to try some experiments. Keep it going fella's!

 

[DrMike]

Ah, yes, the experimentation would be delightful. A formula that accurately predicted OBT would be interesting. I suspect, however, that the changes would be negligible at best when all the variables have been factored in. Still, that is the sort of stuff that can get the creative juices flowing. It is the suggestive power to other factors that could prove valuable ultimately.

 

[joelkdouglas]

I played with OBT for a while. I found some loads that matched OBT pretty closely, and others (30-06, 57.5 gr IMR4350 with a 165 CC for one) that I could not figure out the OBT thing that still shot very well.

I do think it matters, but I think bullet choice, powder pressure in an optimum zone, consistent barrel, etc. matter just as much or more. I think OBT is only one of the considerations.

 

[Dwh7271]

On the harmonics through the various steel, how significant is the variance between say stainless, blued etc? Granted there are differences in formulation but still being "steel", are the differences significant enough to make a major variance in the results?

 

[Oldtrader3]

There are big differences in alloy content and grain structure between martensitic and austenitic steels.