A case for the .750 tenon on a RFBR rifle

[gunsandgunsmithing]

Tony, I often point this program out to people that automatically assume that a fatter barrel is stiffer than a smaller but shorter one..and sometimes it is, but not always.

In tuner design, I made a fixture that I can screw a bbl into, place a known weight at the muzzle, and measure actual deflection. It works but Dan Lilja put it into computer code and made it available to us as a part of his bbl weight calculator program.

I'll link it but first, it's good to read the details about it. Here's a link to the article. I suggest you read it before going straight to the program.
https://riflebarrels.com/a-look-at-the-rigidity-of-benchrest-barrels/

..and here's a link for it. I prefer the excel version. Use the BR bbl program. You can go in and modify bbl dimensions..such as changing from a 27" 1.250 straight to a 27" .900 straight. It can be frustrating at first but is very useful and telling, in regard to bbl droop. It might change your perspective about bbl stiffness, actual bbl droop amounts and why rf bbls aren't stiffer...err, bigger. Bottom line, a 27" 1.25 straight is
3.731 times stiffer than a 27" .900 straight.
https://riflebarrels.com/computer-software/

Another point, fwiw. I have a Pressure Trace system to measure relative chamber pressures and graph them out. They use a strain gage that measures the stretch of the bbl diameter and converts that to electricity. This provides a voltage that can be graphed on a computer screen. Over a 1.250 bbl shank, I can see the primer light off. Point being, bbls grow under pressure.

One more point. As the pressure falls, the bbl is stretched less. Hence, a natural choke in all bbls, to some degree. Not to mention, most rf tuners are clamped onto the muzzle, tensioning the bbl at the muzzle end and significantly reducing stretch, if not constricting the bore a bit.--Mike Ezell

Sorry, but I keep thinking of other points..

So, if we have .007052 deflection over 27" of .900 straight and lets say .250 of bearing surface, that's .0002611/inch divided by 4= roughly 65 millionths of and inch. The 1.250 will be 3.731 times less than THAT, of bullet deformation.

Or would it be less due to the area of the bore and it being more solid like, with that lead slug in it?

I think you get my point, regardless.

 

[Jay Christopherson]

Jay,

A barrel that long has a droop no matter how thick it is. That droop deforms the bullet when passing through the crest. Lead bullets can not spring back. But a jacketed bullet can, especially under a lot of pressure.

TKH

I'll admit I hadn't given this much thought, but I can't see how this can be true (or proven with actual data). I'm not gonna lie, that does not sound like science.

Barrel droop is certainly incontestable and lead certainly has no springback to it, but the rest of it... not sure I'm buying what's being sold here as an explanation for why a .750" diameter tenon is somehow the magic number in a RF setup.

 

[davidjoe]

Sorry, but I keep thinking of other points..

So, if we have .007052 deflection over 27" of .900 straight and lets say .250 of bearing surface, that's .0002611/inch divided by 4= roughly 65 millionths of and inch. The 1.250 will be 3.731 times less than THAT, of bullet deformation.

Or would it be less due to the area of the bore and it being more solid like, with that lead slug in it?

I think you get my point, regardless.

Guns, the bend in a bullet is going to be a whole lot less than even that small amount, I think. I am curious though how that .9 x 27 inch barrel can have basically a minute of angle of droop. That seems truly terrible to me, and happily a 1.25 straight shows to be multiples better.

You can consider the total drop of the 27 inch barrel, but it’s the greatest angular delta (change) in a given .25 inch-long span of travel down the barrel that would impart the presumed bend, (because the front and rear of the bearing surface are .25 inches apart and have to be in that “curve” at the same time in order to bend) and that angle change in only a quarter inch of travel, converted back to inches of bend, is almost infinitesimally small.

And then, whatever that bend is, the fact that the bullet is spinning largely negates even it, as does the no-load-bearing-straight end of the barrel that forces its straighter shape back on the bullet.

 

[Hi-NV Shooter]

I'll admit I hadn't given this much thought, but I can't see how this can be true (or proven with actual data). I'm not gonna lie, that does not sound like science.

Barrel droop is certainly incontestable and lead certainly has no springback to it, but the rest of it... not sure I'm buying what's being sold here as an explanation for why a .750" diameter tenon is somehow the magic number in a RF setup.[/QUOTE]

More evidence happened today, a .750 tenon rifle won todays inaugural Vudoo Bullet Pro 150 RFBR
rifle I believe was built by Bill Calfee, who has pioneered the .750 tenon. it also had a barrel brand which was considered not suitable.
I will say it again the only thing CF that can be applied to RFBR is how to read the wind in that aspect it doesn't change.

Lee

 

[davidjoe]

^^ This match was a big one. Can someone put up the scores?

Comments on the guns used?

 

[RAVAGE88]

Lee, you weren’t there, so you’d have no way of knowing there were no “large diameter” rifles competing in anything other than Factory Hot Rod as repeaters, so let’s keep this relevant. The only rifles in Unlimited were 2500’s and the WLM. This tenon debate is ridiculous....

MB

 

[Hi-NV Shooter]

Lee, you weren’t there, so you’d have no way of knowing there were no “large diameter” rifles competing in anything other than Factory Hot Rod as repeaters, so let’s keep this relevant. The only rifles in Unlimited were 2500’s and the WLM. This tenon debate is ridiculous....

MB

Mike, I did not say there were no large tenon rifles there. It is not a debate, relevant, I stated fact to someone who was comparing CFBR to RFBR. that a .750 tenon action won today.
and until the larger tenon rifles start to win which will happen I am sure. the comparison will not go away, just have to face the fact, just like how more MD-PAS rifles win, because nearly all that dominate RFBR shoot them only. so percentages will favor them. yes a WLM rifle won, but the driver is considered one of the best wind readers in RFBR. he could have used any action and would probably have still won.

That is what any shooter RFBR is facing, it is not just the action.

I am a fan of Anschutz match 54 in particular, and I think they are .810 I no longer even own a custom action go figure.

Lee

 

[RAVAGE88]

Mike, I did not say there were no large tenon rifles there. It is not a debate, relevant, I stated fact to someone who was comparing CFBR to RFBR. that a .750 tenon action won today.
and until the larger tenon rifles start to win which will happen I am sure. the comparison will not go away, just have to face the fact, just like how more MD-PAS rifles win, because nearly all that dominate RFBR shoot them only. so percentages will favor them. yes a WLM rifle won, but the driver is considered one of the best wind readers in RFBR. he could have used any action and would probably have still won.

That is what any shooter RFBR is facing, it is not just the action.

I am a fan of Anschutz match 54 in particular, and I think they are .810 I no longer even own a custom action go figure.

Lee

What you’re saying makes sense Lee, so much so, that what you really said was, the win had more to do with the driver than the tenon....now, it’s a relevant conversation.

MB

 

[gunsandgunsmithing]

I wasn't there either..but I know what conditions were like 2 hrs west of there and it was no day to assess equipment. Pretty bad, with occasional t-storms for much of the day.

 

[gunsandgunsmithing]

Guns, the bend in a bullet is going to be a whole lot less than even that small amount, I think. I am curious though how that .9 x 27 inch barrel can have basically a minute of angle of droop. That seems truly terrible to me, and happily a 1.25 straight shows to be multiples better.

You can consider the total drop of the 27 inch barrel, but it’s the greatest angular delta (change) in a given .25 inch-long span of travel down the barrel that would impart the presumed bend, (because the front and rear of the bearing surface are .25 inches apart and have to be in that “curve” at the same time in order to bend) and that angle change in only a quarter inch of travel, converted back to inches of bend, is almost infinitesimally small.

And then, whatever that bend is, the fact that the bullet is spinning largely negates even it, as does the no-load-bearing-straight end of the barrel that forces its straighter shape back on the bullet.

It might make more sense if you read the lilja article I linked. But feel free to check my math. I'm open to correction. I didn't bother with converting it to angle, only amount.

 

[Jay Christopherson]

so... because a 0.750 tenon won, that constitutes evidentiary proof of it's superiority. Just out of curiosity, how many NON-.750 tenons did that rifle prove it's now undeniably self-evident superiority against?

 

[gunsandgunsmithing]

Guns, the bend in a bullet is going to be a whole lot less than even that small amount, I think. I am curious though how that .9 x 27 inch barrel can have basically a minute of angle of droop. That seems truly terrible to me, and happily a 1.25 straight shows to be multiples better.

You can consider the total drop of the 27 inch barrel, but it’s the greatest angular delta (change) in a given .25 inch-long span of travel down the barrel that would impart the presumed bend, (because the front and rear of the bearing surface are .25 inches apart and have to be in that “curve” at the same time in order to bend) and that angle change in only a quarter inch of travel, converted back to inches of bend, is almost infinitesimally small.

And then, whatever that bend is, the fact that the bullet is spinning largely negates even it, as does the no-load-bearing-straight end of the barrel that forces its straighter shape back on the bullet.

I do agree with your point about maximum angular change. I'm not sure how much twist matters, due to a typical rimfire twist rate is along the lines of 1 turn in 16 inches.
Another factor, for better or worse, is Tony's oversimplification of how the bbl bends. It's not a single, long and sweeping arc.

That said, until now, I dont think I've mentioned anything centerfire...or specific to cf or rf. Instead, I think the same calculations apply equally to either bbl of these dimensions regardless of where the primer compound is located in the case. If anything, the natural frequency of each bbl is the same, be it rf or cf, respectively..but amplitude will be more with cf..bigger hammer. The higher amplitude would almost certainly impart more angular change. Fwiw.

 

[RAVAGE88]

I find it really interesting that a “case” has to be built at all. It’s as if, there’s some reason to defend one vs the other, why do you think that is?

MB

 

[Hi-NV Shooter]

I find it really interesting that a “case” has to be built at all. It’s as if, there’s some reason to defend one vs the other, why do you think that is?

MB

Mike, Why does it matter? The information Tony posted makes sense to me for the reason behind the .750 tenon and was something I never knew.
as far as defending it, I didn't read it as such. but it did validate somewhat, what I been playing with as far as barrels go.

Lee

 

[RAVAGE88]

Mike, Why does it matter? The information Tony posted makes sense to me for the reason behind the .750 tenon and was something I never knew.
as far as defending it, I didn't read it as such. but it did validate somewhat, what I been playing with as far as barrels go.

Lee

And that’s why I enjoy our exchanges Lee, you always ask awesome questions. And I agree, what Tony posted is great info, but it can easily be read as a one vs the other post instead of being purely for info. That’s why others are asking the questions we see.

MB

 

[gunsandgunsmithing]

And that’s why I enjoy our exchanges Lee, you always ask awesome questions. And I agree, what Tony posted is great info, but it can easily be read as a one vs the other post instead of being purely for info. That’s why others are asking the questions we see.

MB

Mike, respectfully, I've not asked questions, but posted resources that factually prove some of his comments as incorrect concerning bbl droop and bullet deformation qualification. Tony's a hell of a guy and shooter but the info is out there to all of us that wish to better understand this aspect of the discussion.

Often there is no real need in knowing how what we do, does what it does. But when that turns to unqualified and just incorrect information on the web, it just confuses things for everyone.

Art belongs in museums. We should all focus on the actual science and/or physics behind what we want to better understand.

Or...just shoot and do what works! Either way is good.

I posted the links. I think anyone remotely interested, should read the article and play with the program a bit.

 

[Hi-NV Shooter]

And that’s why I enjoy our exchanges Lee, you always ask awesome questions. And I agree, what Tony posted is great info, but it can easily be read as a one vs the other post instead of being purely for info. That’s why others are asking the questions we see.

MB

Mike, It would be great if you started a thread on why a larger tenon is another option. the only thing I know and read was the fact the 40X was originally a CF and when they made it into a RF they kept the CF tenon size this is the only RF action from the past that uses it.
as I said I like Anschutz 150+ years of experience and they used a .780 tenon on the match 54 this is way before the .750 tenon they also have an off-set bolt race as well as a recoil lug. the Anschutz engineers must have known something.

Lee

 

[gunsandgunsmithing]

Now I'll ask a question. Am I reading some of this right. Am I to believe that removing metal from the muzzle makes it grow but removing more metal from the breech, than it takes to get a .750 tenon, creates a tight spot? Serious question.

I'm a tool and die guy so I can understand the bore opening after turning down, relieving stress and how it would not open at the unturned portion, where the shoulder is. What I don't understand is how the bore will get smaller at the area that is not machined, regardless of if it's .750 or 1.0625. It would seem that, if anything, the change would be less with less machining. And it seems the fix might be a shorter tenon...if this actually occurs at all.

Admittedly, it's been a crazy last few days(weeks) with family health issues. I might have missed something.

 

[RAVAGE88]

Mike, respectfully, I've not asked questions, but posted resources that factually prove some of his comments as incorrect concerning bbl droop and bullet deformation qualification. Tony's a hell of a guy and shooter but the info is out there to all of us that wish to better understand this aspect of the discussion.

Often there is no real need in knowing how what we do, does what it does. But when that turns to unqualified and just incorrect information on the web, it just confuses things for everyone.

Art belongs in museums. We should all focus on the actual science and/or physics behind what we want to better understand.

Or...just shoot and do what works! Either way is good.

I posted the links. I think anyone remotely interested, should read the article and play with the program a bit.

I agree with you 100% and although I will always accommodate effort, there are details that are beyond the grasp of those that don’t get the science.

On the surface, what Tony posted is good info, hence my appreciation for posting good info, but there’s a divergent point where those that can take the conversation farther have to carry on with others that truly understand what you posted, otherwise, the train wreck begins. I’ve learned to just read on without saying more than can be digested but the cool thing is, there are a few that truly think about it and are able to participate at a higher level....Hozzie is a great example of someone that will do this and it’s awesome when Landy gets involved.

Thanks for the links and keep on keepin on.
MB

 

[RAVAGE88]

Mike, It would be great if you started a thread on why a larger tenon is another option. the only thing I know and read was the fact the 40X was originally a CF and when they made it into a RF they kept the CF tenon size this is the only RF action from the past that uses it.
as I said I like Anschutz 150+ years of experience and they used a .780 tenon on the match 54 this is way before the .750 tenon they also have an off-set bolt race as well as a recoil lug. the Anschutz engineers must have known something.

Lee

Thanks Lee, I’ll consider that, but I don’t think I will. The focus area of the subject is extremely narrow and it seems that mathematic facts really piss some guys off. From what I’m seeing though, I believe this will continue to evolve for the better as there are more than a few proving to be intellectually mature enough to participate in a productive conversation without some weirdly strong adherence to anecdotal information.

MB