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

  1. #1
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    A case for the .750 barrel 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 itís 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? Well, 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 itís 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 todayís world Iím sure this writing will be attacked, and Iím 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
    Last edited by tonykharper; 07-31-2020 at 10:41 AM.

  2. #2
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    Well, Tony, that makes sense and was well articulated.
    One followup question. In your opinion, if you end up with a larger action ,for whatever reason, do you give up anything by going with a properly centered/fitted bushing?

  3. #3
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    Quote Originally Posted by tonykharper View Post
    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 remove 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 itís 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? Well, 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 itís 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 todayís world Iím sure this writing will be attacked, and Iím OK with that.

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

    If there is a counter case favoring the large, particularly 1.062 tenons, I for one, would like to hear it.

    TKH

    What about running a larger barrel profile like a straight 1.25 for large tenon actions?

  4. #4
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    Quote Originally Posted by tim View Post
    Well, Tony, that makes sense and was well articulated.
    One followup question. In your opinion, if you end up with a larger action ,for whatever reason, do you give up anything by going with a properly centered/fitted bushing?
    It has been done but as you said it requires a properly centered/fitted bushing.

    That bushing has to be a work of art. It has to be screwed into the actions thread, and shouldered, then remain square and centered when you cut the thread to hold the barrel.

    Not a task for the weak of heart.

    I appreciate you looking at this. I'm not much of a technical writer and I want it to be as clear as possible.

    TKH

  5. #5
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    Quote Originally Posted by TrxR View Post
    What about running a larger barrel profile like a straight 1.25 for large tenon actions?
    Good point, that can be done but most guys want a 23-27 inch barrel on a rimfire and that is a lot of weight to hang out on a short action.

    RFBR barrels are free floated. Well, I know of one that isn't but that is another story.

    If you make the action footprint longer you can solve that too, but you still have a pretty heavy rifle, and of course it could only be used in Unlimited classes.

    TKH
    Last edited by tonykharper; 07-30-2020 at 07:48 PM.

  6. #6
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    Quote Originally Posted by tonykharper View Post
    It has been done but as you said it requires a properly centered/fitted bushing.

    That bushing has to be a work of art. It has to be screwed into the actions thread, and shouldered, then remain square and centered when you cut the thread to hold the barrel.

    Not a task for the weak of heart.

    I appreciate you looking at this. I'm not much of a technical writer and I want it to be as clear as possible.

    TKH
    Very clear Tony.
    We were lucky up here, we had a real master at them.
    You are spot on, from what I know, most guys make a bushing with internal threads and screw'em on....crooked most times.
    Tommy Fargnoli, the guy that made those lovely 40X sporters by making repeaters out of them, complete with 6 o'clock pins, Said you had to thread them while they were into the action And trued up to yield a nice aligned barrel.
    Thanks again Tony.

  7. #7
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    Tkh

    The VooDoo? Does it not have the Large Tenon ? Back in 1989 I worked for a company that had its own Main Frame Computer , What a Beast it was ! Had it`s own 20x30 air conditioned room ! The Russians are still building the Belarus Ag Tractors that are 1954 technology and cheaper than dirt ! It`s amazing to me that in 2020 engineers want to reinvent the wheel ! Time Precision that TKH once competed with was another beast and I still have one of them relics ! The question TKH , how could this happen ?

    Sputnik is alive and well !
    Last edited by Slick Willy; 07-31-2020 at 09:37 AM.

  8. #8
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    Cool

    Quote Originally Posted by tonykharper View Post
    good point, that can be done but most guys want a 23-27 inch barrel on a rimfire and that is a lot of weight to hang out on a short action.

    Rfbr barrels are free floated. Well, i know of one that isn't but that is another story.

    If you make the action footprint longer you can solve that too, but you still have a pretty heavy rifle, and of course it could only be used in unlimited classes.

    Tkh
    some yrs ago i built 2 rimfire s with 18 inch barrels thru talking with jim stele of rem.most acc. I have ever seen

  9. #9
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    Cool

    Quote Originally Posted by billbrawand View Post
    some yrs ago i built 2 rimfire s with 18 inch barrels thru talking with jim stele of rem.most acc. I have ever seen
    afew months ago i chambered 4 new rimfire barrels for unl. Same length as they came shot one it shot in one outside at 50 yds

  10. #10
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    Quote Originally Posted by Slick Willy View Post
    The VooDoo? Does it not have the Large Tenon ? Back in 1989 I worked for a company that had its own Main Frame Computer , What a Beast it was ! Had it`s own 20x30 air conditioned room ! The Russians are still building the Belarus Ag Tractors that are 1954 technology and cheaper than dirt ! It`s amazing to me that in 2020 engineers want to reinvent the wheel ! Time Precision that TKH once competed with was another beast and I still have one of them relics ! The question TKH , how could this happen ? Sputnik is alive and well !
    Slick,

    First I would like to thank you for your very excellent, well worded, and succinct questions.

    The VooDoo? Does it not have the Large Tenon ?

    I believe it does, but so far it is unproven as a RFBR action. Please advise when it reaches that status so I can update my records.

    Back in 1989 I worked for a company that had its own Main Frame Computer , What a Beast it was ! Had it`s own 20x30 air conditioned room !

    Yes!

    The Russians are still building the Belarus Ag Tractors that are 1954 technology and cheaper than dirt !

    I get it, if it is cheap enough people will buy it??


    It`s amazing to me that in 2020 engineers want to reinvent the wheel !

    It is their nature.

    Time Precision that TKH once competed with was another beast and I still have one of them relics ! The question TKH , how could this happen ?

    Time Precision sponsored me as a shooter back in the day. Provided rifles, barrels, tuners, rests, etc. If you study the time actions you will see they also have a large tenon. They also had front locking lugs. Art was a pretty smart guy. He tapered his barrels and used a special type of fluting.

    This fluting started very deep at the chamber end and faded out at the muzzle. His thinking was this helped to keep the bore fairly uniform.
    He once told me he really liked the ones that showed a slight taper to the muzzle, but admitted not all of them did.

    As you know his rifles were pretty successful. People said they were too hard to load but that never bothered me until the arthritis kicked in.

    Sputnik is alive and well !

    So am I, and hope you and yours are too.

    Thanks again for the questions. I can only hope my answers meet with your approval.

    TKH
    Last edited by tonykharper; 07-31-2020 at 10:11 AM.

  11. #11
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    One advantage

    to the big tenon. There are those that believe the part of the barrel that meets the face needs to be larger than 0.900. (I am not necessarily one of them btw). There are good smiths in this sport that like the old #7 contour Shilens and R0 or Ross tapers also. IF that is the case and IF the barrel maker or person lapping the barrel laps it correctly with a taper, the situation changes. In my mind the big plus of the smaller barrels is our knowledge of tuning them. The R0 or Ross retains that. IF we now have that correctly lapped barrel we need to install it. When the tenon is cut, the barrel expands (if a button) and that may or may not be a disaster. Cutting a 1.200 diameter to 0.750 causes more distortion than going to 1.0625. In that case, the finished barrel on the large tenon will more closely resemble the initial shape. It also gives more surface area at a larger radius on the action face, in either case which gives better structural support. In the large tenon case, the torque in which you tighten the barrel to matters MUCH less.

    All that being said, IF THE R0 OR ROSS TAPER BARREL IS LAPPED SUCH THAT IT LOOKS LIKE A PERFECTLY LAPPED 0.900 BLANK, (that's not impossible btw) I might go for the big tenon action over the small for:
    1. more face contact and
    2. less tightening torque distortion.

    In the end, if I am going to build actions for the masses, I will build a 0.750 tenon IF the action design allows for it. (tough on center lockup). I may also build myself a large tenon and experiment though. The big kicker there is that I have the ability to lap my own barrels. Truth be told, on anything other than a straight 0.900, I rough cut the tenon before I lap it anyways for reasons listed above.

  12. #12
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    Quote Originally Posted by Slick Willy View Post
    ...It`s amazing to me that in 2020 engineers want to reinvent the wheel ! ...[/B]
    Be careful Slick. If engineers didn't change things and "reinvent the wheel" as you would say, all of us would be still using them old tractors. 35 years ago EVERYONE hated fuel injection and electronic ignition. If you tried to go back to carbs and points in today's world, you would have a riot. Just because something we have now works, it doesn't mean it can't be done better.

  13. #13
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    Quote Originally Posted by stiller View Post
    to the big tenon. There are those that believe the part of the barrel that meets the face needs to be larger than 0.900. (I am not necessarily one of them btw). There are good smiths in this sport that like the old #7 contour Shilens and R0 or Ross tapers also. IF that is the case and IF the barrel maker or person lapping the barrel laps it correctly with a taper, the situation changes. In my mind the big plus of the smaller barrels is our knowledge of tuning them. The R0 or Ross retains that. IF we now have that correctly lapped barrel we need to install it. When the tenon is cut, the barrel expands (if a button) and that may or may not be a disaster. Cutting a 1.200 diameter to 0.750 causes more distortion than going to 1.0625. In that case, the finished barrel on the large tenon will more closely resemble the initial shape. It also gives more surface area at a larger radius on the action face, in either case which gives better structural support. In the large tenon case, the torque in which you tighten the barrel to matters MUCH less.

    All that being said, IF THE R0 OR ROSS TAPER BARREL IS LAPPED SUCH THAT IT LOOKS LIKE A PERFECTLY LAPPED 0.900 BLANK, (that's not impossible btw) I might go for the big tenon action over the small for:
    1. more face contact and
    2. less tightening torque distortion.

    In the end, if I am going to build actions for the masses, I will build a 0.750 tenon IF the action design allows for it. (tough on center lockup). I may also build myself a large tenon and experiment though. The big kicker there is that I have the ability to lap my own barrels. Truth be told, on anything other than a straight 0.900, I rough cut the tenon before I lap it anyways for reasons listed above.
    Jerry, thank you for bring your knowledge and experience to the conversation.

    Your points are well taken:

    1. more face contact and
    2. less tightening torque distortion.

    Do you see this to be a problem with many RFBR .900 barrels?

    The ones I see don't take much to break them loose.

    The take away here is don't over torque the barrel.

    If you don't mind saying what number do you torque barrels to.

    TKH

  14. #14
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    I have a Meyers action

    I had Killough build the rifle and it came with Ross taper Shilen barrel Gorham chambered for it. The rifle didn't shoot competitively, really. After some time I looked with a bore scope and saw a flaw in the barrel from Manufacturing. Sent the barrel back and they sent me a new replacement. I fitted it myself and it shoot OK but not "Killer" as someone says but the more rounds I've put through it, the better it has shot. I also have a bushing I bought from Dan. I have yet to fit a barrel with the bushing that has shot as well as the barrel I have now. It may make a pretty good case for the large tenon or maybe just happenstance but Id agree with Jerry on the size thing at this point.

    Pete

  15. #15
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    Regarding Lapping:

    In the not too distant past anyone but a barrel maker who lapped and admitted it was chastised and called an idiot for doing it, how dare anyone even touch the inside of their barrel. Its good to see others doing it, talking about it and not be crapped on for mentioning it.

    Pete

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