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A case for the .750 tenon on a RFBR rifle

A case for the .750 tenon on a RFBR rifle!

All custom RFBR action makers use the .750 tenon. Why?

It has nothing to do with strength, hoop strength, or union strength.

The primary reason for the smaller tenon is to be able to use straight profile barrels.

There is no magic in the .750 number, .740, .725 etc. etc. would work just as well.

The key is the tenon needs to be small enough to fit a straight profiled .800 - .950 barrel and leave enough shoulder to secure the barrel to the action face.

Straight profile barrels have been preferred in RFBR for a long time.

There was a time rimfire smiths would make bushings to allow straight profile barrels to be fit to the large tenon holes.

Some 40Xs, and clones are still shot this way.

Why do today's RFBR rifles use straight profile barrels?

The reason is if you profile a barrel removing metal from the outside of a barrel you change the dimensions of the bore inside the barrel.

The bore increases in size as the stress is relieved by removing outer metal.

This is settled science; many metallurgy books will confirm this.

The point is, if you make a barrel and finish the bore, when you profile the outside of the barrel you change the bore.

Now if you remove an equal amount of metal from the entire length of the barrel you have changed the bore it’s entire length,

but if you leave a big knot on one end, for a large tenon, you have not opened up the bore in that location.

You have created a restriction at the chamber end of the barrel.

This restriction can be removed. It can be lapped out by someone with those skills.

Some even say if the barrel is shot enough it will eventually work out.

Is the change inside the barrel enough to affect accuracy? If we are talking minute of a moose accuracy probably not, but if we are talking ultimate accuracy yes.

The reason reverse tapered barrels were once popular was because reverse profiling induced a taper in the bore.

Reverse tapered barrels are still used on nearly all IR 50/50 sporters. This method works, but not as good as lapping with a lead lap.

To sum up, we can all cite cases where 40Xs, and it’s copies, Annies, and Suhls have done well in RFBR with large tenons.

These are the exceptions to the rule. I can only recall one Annie, and two Suhls, and perhaps a 40X or two that have had an impact on RFBR in the last 10 years.

The rule today is to use straight profiled barrels. Even with straight profiles it can be hard to find a real killer.

Many very smart people have been chasing rimfire accuracy for a very long time.

If you follow the trends of what works most often you can learn the direction to go.

In today’s world I’m sure this writing will be attacked, and I’m OK with that.

I took the time to put this together to help those that want to understand my perspective.

I come to these forums to learn and if there is a counter case favoring the large, particularly 1.062 tenons, I for one, would like to hear it.

TKH
 
To
A case for the .750 tenon on a RFBR rifle!

All custom RFBR action makers use the .750 tenon. Why?

It has nothing to do with strength, hoop strength, or union strength.

The primary reason for the smaller tenon is to be able to use straight profile barrels.

There is no magic in the .750 number, .740, .725 etc. etc. would work just as well.

The key is the tenon needs to be small enough to fit a straight profiled .800 - .950 barrel and leave enough shoulder to secure the barrel to the action face.

Straight profile barrels have been preferred in RFBR for a long time.

There was a time rimfire smiths would make bushings to allow straight profile barrels to be fit to the large tenon holes.

Some 40Xs, and clones are still shot this way.

Why do today's RFBR rifles use straight profile barrels?

The reason is if you profile a barrel removing metal from the outside of a barrel you change the dimensions of the bore inside the barrel.

The bore increases in size as the stress is relieved by removing outer metal.

This is settled science; many metallurgy books will confirm this.

The point is, if you make a barrel and finish the bore, when you profile the outside of the barrel you change the bore.

Now if you remove an equal amount of metal from the entire length of the barrel you have changed the bore it’s entire length,

but if you leave a big knot on one end, for a large tenon, you have not opened up the bore in that location.

You have created a restriction at the chamber end of the barrel.

This restriction can be removed. It can be lapped out by someone with those skills.

Some even say if the barrel is shot enough it will eventually work out.

Is the change inside the barrel enough to affect accuracy? If we are talking minute of a moose accuracy probably not, but if we are talking ultimate accuracy yes.

The reason reverse tapered barrels were once popular was because reverse profiling induced a taper in the bore.

Reverse tapered barrels are still used on nearly all IR 50/50 sporters. This method works, but not as good as lapping with a lead lap.

To sum up, we can all cite cases where 40Xs, and it’s copies, Annies, and Suhls have done well in RFBR with large tenons.

These are the exceptions to the rule. I can only recall one Annie, and two Suhls, and perhaps a 40X or two that have had an impact on RFBR in the last 10 years.

The rule today is to use straight profiled barrels. Even with straight profiles it can be hard to find a real killer.

Many very smart people have been chasing rimfire accuracy for a very long time.

If you follow the trends of what works most often you can learn the direction to go.

In today’s world I’m sure this writing will be attacked, and I’m OK with that.

I took the time to put this together to help those that want to understand my perspective.

I come to these forums to learn and if there is a counter case favoring the large, particularly 1.062 tenons, I for one, would like to hear it.

TKH

Tony, Thank you for posting this information. I also come here and to other forms to learn.
I find it very interesting what you said about what happens when you remove material from a barrel's exterior and how much it can affect accuracy.
I seen this on two barrels which had the chamber end turned down from 1.200 to 1.00 .200 was removed and both barrel shoot very good.
the purpose for doing that was to copy the characteristics of what you said about reverse taper barrels.
based on a bullet can start off (chamber end)slightly larger in the bore is ok, but can not start smaller then try and go larger as lead is a dead material. the same thing, when you slug a barrel, can't be tight then loose then tight that barrel will have problems.
I am planning two more experiments doing the same thing with the chamber end of the barrels, I very confident now more so, on what you provided here that it will be successful like the other two barrels.

Thanks again for sharing, I really appreciate the information.

Lee
 
To


Tony, Thank you for posting this information. I also come here and to other forms to learn.
I find it very interesting what you said about what happens when you remove material from a barrel's exterior and how much it can affect accuracy.
I seen this on two barrels which had the chamber end turned down from 1.200 to 1.00 .200 was removed and both barrel shoot very good.
the purpose for doing that was to copy the characteristics of what you said about reverse taper barrels.
based on a bullet can start off (chamber end)slightly larger in the bore is ok, but can not start smaller then try and go larger as lead is a dead material. the same thing, when you slug a barrel, can't be tight then loose then tight that barrel will have problems.
I am planning two more experiments doing the same thing with the chamber end of the barrels, I very confident now more so, on what you provided here that it will be successful like the other two barrels.

Thanks again for sharing, I really appreciate the information.

Lee

the original theory for .750 straight no tapered bbls was that a tuner would be more effective and easier to adjust for smaller groups.
 
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Very nice post Tony, it’s great to see the movement away from the “support” theory of one vs the other (the train wreck that occurred in my thread) and into more applicable info. I happen to like the smaller tenon where I might take advantage of how it’s best used, but as I’ve said, there are reasons I’m using the larger tenon. I’ve also stated openly, if I were to design the action differently for things outside my current reasoning, I would likely use a smaller tenon, so there’s no basis for challenging anything you’re saying here.

Thank you for posting good info,
MB
 
Very enlightening! Thank you. Question: Are there any makers of profiled barrels that compensate for the change in the bore ? Or, do they assume the accuracy for the average guy buying a profiled barrel is going to be good enough? Some of this probably comes down to economics.
 
Very enlightening! Thank you. Question: Are there any makers of profiled barrels that compensate for the change in the bore ? Or, do they assume the accuracy for the average guy buying a profiled barrel is going to be good enough? Some of this probably comes down to economics.


IMO I would avoid any barrel maker that had a opinion or assumption that accuracy would be good enough for the average guy/shooter.
if a barrel maker will not start off with the intention of producing a hummer out of every barrel they produce again IMO they should be avoided.

Lee
 
As would I, if I knew who they were. I'm just asking because I doubt that I will ever have a straight barreled .22. If I'm spending the time and money on having a rifle built I would want to end up with something that is more consistently accurate than a1k off the shelf rifle.
 
the original theory for .750 straight no tapered bbls was that a tuner would be more effective and easier to adjust for smaller groups.

Bob,

Many still believe straight profile barrels of any size are easier to tune than barrels with knots and lumps.

I don't know the truth so I didn't mention it in my post.

Thank you for pointing that out.

TKH
 
As would I, if I knew who they were. I'm just asking because I doubt that I will ever have a straight barreled .22. If I'm spending the time and money on having a rifle built I would want to end up with something that is more consistently accurate than a1k off the shelf rifle.

I understand. I can't speak for other makers as I only have experience using Benchmark barrels and I can say of the 5 I had chambered they all shot really good with the last one being the experiment I mention here, being capable of shooting sub.200 ctc groups without a tuner.
but Muller and Shilen are the top RFBR barrel makers with probably Shilen being the most popular due to availability.

Lee
 
Bob,

Many still believe straight profile barrels of any size are easier to tune than barrels with knots and lumps.

I don't know the truth so I didn't mention it in my post.

Thank you for pointing that out.

TKH

Tony, from what I understand and from my own experience reverse taper barrels are finicky when trying to tune them not sure because of the extra weight already at the muzzle from the taper.

Also do you think what the barrel is made of makes a difference like SS vs CM ?

Lee
 
A case for the .750 tenon on a RFBR rifle!

All custom RFBR action makers use the .750 tenon. Why?

It has nothing to do with strength, hoop strength, or union strength.

The primary reason for the smaller tenon is to be able to use straight profile barrels.

There is no magic in the .750 number, .740, .725 etc. etc. would work just as well.

The key is the tenon needs to be small enough to fit a straight profiled .800 - .950 barrel and leave enough shoulder to secure the barrel to the action face.

Straight profile barrels have been preferred in RFBR for a long time.

There was a time rimfire smiths would make bushings to allow straight profile barrels to be fit to the large tenon holes.

Some 40Xs, and clones are still shot this way.

Why do today's RFBR rifles use straight profile barrels?

The reason is if you profile a barrel removing metal from the outside of a barrel you change the dimensions of the bore inside the barrel.

The bore increases in size as the stress is relieved by removing outer metal.

This is settled science; many metallurgy books will confirm this.

The point is, if you make a barrel and finish the bore, when you profile the outside of the barrel you change the bore.

Now if you remove an equal amount of metal from the entire length of the barrel you have changed the bore it’s entire length,

but if you leave a big knot on one end, for a large tenon, you have not opened up the bore in that location.

You have created a restriction at the chamber end of the barrel.

This restriction can be removed. It can be lapped out by someone with those skills.

Some even say if the barrel is shot enough it will eventually work out.

Is the change inside the barrel enough to affect accuracy? If we are talking minute of a moose accuracy probably not, but if we are talking ultimate accuracy yes.

The reason reverse tapered barrels were once popular was because reverse profiling induced a taper in the bore.

Reverse tapered barrels are still used on nearly all IR 50/50 sporters. This method works, but not as good as lapping with a lead lap.

To sum up, we can all cite cases where 40Xs, and it’s copies, Annies, and Suhls have done well in RFBR with large tenons.

These are the exceptions to the rule. I can only recall one Annie, and two Suhls, and perhaps a 40X or two that have had an impact on RFBR in the last 10 years.

The rule today is to use straight profiled barrels. Even with straight profiles it can be hard to find a real killer.

Many very smart people have been chasing rimfire accuracy for a very long time.

If you follow the trends of what works most often you can learn the direction to go.

In today’s world I’m sure this writing will be attacked, and I’m OK with that.

I took the time to put this together to help those that want to understand my perspective.

I come to these forums to learn and if there is a counter case favoring the large, particularly 1.062 tenons, I for one, would like to hear it.

TKH

How is it that centerfire (including BR) are able to easily run no contour barrels at at 1.250" diameter running more than 28" in length with tenon diameters that are commonly larger than 1“ diameter?

I understand that I am not a RF BR competitor, but the theory behind the reason being stated here doesn't make sense to me. It sounds more like a pet theory that has persisted through generations as "this is how it has always been done"
 
How is it that centerfire (including BR) are able to easily run no contour barrels at at 1.250" diameter running more than 28" in length with tenon diameters that are commonly larger than 1“ diameter?

I understand that I am not a RF BR competitor, but the theory behind the reason being stated here doesn't make sense to me. It sounds more like a pet theory that has persisted through generations as "this is how it has always been done"

Jay,

That is a great question and one of many that makes it hard for a centerfire smith to do great rimfire barrel work.

The answer is in the lead bullet we shoot vs the jacketed bullets used in centerfire. Of course there are many other factors such as speed and pressures.

Those centerfire actions that hold those 1.250 barrels 28 inches long must have a very long foot prints.

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.

This is one reason taper to a rimfire barrel is important. Centerfire guys don't even think about bore taper.

This is no "this is how it has always been done" even after all these years we are learning more everyday.

What I stated here is settled science. It is well documented.

Thank you for your question. I'm sure there are many other centerfire guys wondering the same.

TKH
 
I read the other thread too. I’m almost positive the original reason for a small tenon in RF relative to CF was that the actions were smaller (like the 52) except for the 40-X, and those patterning it.

That tiny cartridge chamber removed so little material (strength) that the chamber wall at .75 is still as beefy as a ~1 inch tenon with say a 300 win mag cut out of it, and plenty strong for a straight barrel that is downsized just like the 52, Anshutz, Kimber etc actions are downsized.

The 40-X is a 1.35” action and it would honestly look ridiculous (and waste it’s inherent strength) to use any smaller diameter barrel than Remington used, which was something like a 1.20 to .85. Bigger replacements are possible though because of its diameter. I would personally not choose to downsize a tenon given a choice. I run barrels as thick as 2.0 straight and the tenon, not my generously built actions, is where my mind goes in contemplating weak points.

I have 52’s and 40-X’s in Rimfre. I don’t think you must have a 1.35” action for an ultra-accurate Rimfre but I would go to the mat over the idea that an action or barrel any manufacturer has been willing to make could be too heavy for accuracy. BR knows that weight done right is the friend of accuracy. In all of shooting, there is not a minimum weight rule, for good reason. I do know you’re not saying otherwise, I am just saying...
 
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Tony, from what I understand and from my own experience reverse taper barrels are finicky when trying to tune them not sure because of the extra weight already at the muzzle from the taper.

Also do you think what the barrel is made of makes a difference like SS vs CM ?

Lee

Lee,

I haven't spent a lot of time with CM barrels. I know they are hard to machine compared to SS.

I've never found reverse tapers to be hard to tune. They are used today on nearly every IR 50/50 sporter.

Rules do not allow adjustable tuners. However, they are tuned by leaving a 2-3 inch dog knot on the muzzle end of the barrel and counter boring it to achieve tune. The idea being to get weight out beyond the crown.

TKH
 
Jay,

The answer is in the lead bullet we shoot

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.

This is one reason taper to a rimfire barrel is important. Centerfire guys don't even think about bore taper.



TKH

Tony, if a .22 bullet gets “bent” by the barrel’s droop, (despite a very short bearing length) then it’s going to be straightened out again at the end of the barrel. The muzzle end of a barrel is not supporting any other weight and is as straight as can be made.
 
Tony, if a .22 bullet gets “bent” by the barrel’s droop, (despite a very short bearing length) then it’s going to be straightened out again at the end of the barrel. The muzzle end of a barrel is not supporting any other weight and is as straight as can be made.

Jay,

I think you are right it will be straight but will the side bearing surface spring back, or will one side grow? Will it still be balanced when it leaves the crown?

Kinda like bent metal. Once deformed very hard for it to return to shape perfectly. Lead is inert it just doesn't have any spring back in it.

Jackets with nice bases, and lots of pressure helps centerfire bullets.

TKH
 
And here I thought the subject of how many angels can dance on the head of a pin was tedious and unprovable....
 
Jay,

That is a great question and one of many that makes it hard for a centerfire smith to do great rimfire barrel work.

The answer is in the lead bullet we shoot vs the jacketed bullets used in centerfire. Of course there are many other factors such as speed and pressures.

Those centerfire actions that hold those 1.250 barrels 28 inches long must have a very long foot prints.

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.

This is one reason taper to a rimfire barrel is important. Centerfire guys don't even think about bore taper.

This is no "this is how it has always been done" even after all these years we are learning more everyday.

What I stated here is settled science. It is well documented.

Thank you for your question. I'm sure there are many other centerfire guys wondering the same.

TKH
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
 
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