Gene Beggs ???

D

Don Nielson

New member
In all the discussions of thread pitch I don't see anything about diameters? What is the O.D. of the tenon that goes into the bushing? Can anyone do a stess analysis on a smaller tenon?

I started a new thread so this wouldn't get lost. Don
 
Don Nielson said:
In all the discussions of thread pitch I don't see anything about diameters? What is the O.D. of the tenon that goes into the bushing? Can anyone do a stess analysis on a smaller tenon?

I started a new thread so this wouldn't get lost. Don
Click to expand...


Hi Don, nice to hear from you. :)

When working with an action with 1.063 X 18 tpi threads, it gets a little crowded in the front receiver ring. So far, I have made three prototypes each time reducing the tenon diameter. The first one started off at .900 before threading and I used 28 tpi. Of course, this made the bushing thickness pretty thin but it shoots great and in spite of full case loads of H4198 in my 6 Beggs with 68 grain bullets the threads torque up tight and do not loosen after firing many rounds. You can put the thickness in the tenon or the adjustable bushing. It probably does not matter because it all adds up to the same dia., anyway.

My second prototype used a .875 tenon with 28 tpi. This made the bushing a little thicker. It also shot and worked fine. I made a third prototype today with the smallest tenon yet at .800 threaded 24 tpi. Just looking at it, the tenon looks pretty small but the bushing is much thicker. I don't know which installation is stronger. Any way you look at it there is still basically the same amount of steel around the chamber so it probably does not matter.

Admittedly, I have some concern about the reduced wall thickness of the chamber. My greatest concern is for safety. I hope Jerry Stiller will do a structural analysis for me.

Except for a rimfire, I don't think it would be practical or safe to use this system with an action that has front receiver ring threads smaller than 1.0630. The only actions I have worked with so far are the Viper and Cobra drop ports. I don't know how it's going to work with a coned breach like the Panda's.

With your OmniTurn you can program it to turn out parts with miminum clearance. If you decide to try it, I would suggest using a tenon diameter of .875 threaded 24 tpi with minimum clearance. Make the bushing .875 in length and cut two 5/32 keyway slots in the rear of the bushing. Old barrel stubs work great.

You can make a screwdriver type tool to go in from the rear of the action and engage the two slots. I drilled the tool shaft with a #3 drill to accept a 5/32 x one inch sqare key securing it with a small set screw. I had to grind on the key a little to get it to fit the slots. With this tool, you can snug up the bushing with the barrel in place and then tighten to full torque with a barrel vise and action wrench.

Keep in touch. Hope this makes sense.

Later,

Gene Beggs
 
This is slightly off the subject but I recently received one of the large tenon BAT's just because I want to shoot a very high pressure magnum and several folks that I'd talked to were of the opinion that the tenon takes the entire bursting load.........

Now I'm no engineer and to me it "stands to reason" that even in the event of rupture the additional rings of steel would act to contain the burst event but what do I know :rolleyes: It could also be that the bursting of a too-small tenon could initiate a devastating chain effect.... I have no idea.

In short, I'm very interested in the analysis as done by someone like Stiller.

Please :)

al
 
Ooops, looks like Stiller already DID opine on the subject over on The Mother Of All Indexing Threads...

I'd still be interested to hear a more if one of the BigHeads would care to share....

Please :)

al
 
Al,
It may not be so much about bursting as when one arrives at a tight bolt. A long time ago, I read of a comparison between Remington (1 1/6" tenon) and Winchester (1" tenon) both with belted magnum barrels of the same caliber. It was the the author's experience that the Remington has the higher sticky bolt pressure of the two. Gene is shooting cases that have more taper than the PPC and it may be that it takes more pressure for them to get to a sticky bolt (or not). It will be interesting to see how all of this tracks as more shooters try his system.

One more thing about action thread size, Savage has increased the tenon diameter slightly on some of their later model actions without changing the action diameter. Could this be an option for those that want a slightly larger tenon with an indexing bushing? In combination with a Remington lug style washer that was round and functioned only to increase a standard barrel's shoulder contact (on a glue-in) ,there might be some slight advantage.
 
Barrel shank strength

For the arrangement I suggested in another post this was my comment on strength of the shank.
Stress in the shank would be approx. 1.6 times the internal pressure in the chamber, that is if you had 50000 case pressure then the hoop stress in the shank would be about 80000 psi.
My sketch may not be exactly the way Gene is doing it but it's still only necessary to consider the ratio of shank o.d. to it's i.d. It depends on the steel's yield strength but I believe a ratio of 2 or more will have sufficient strength. Here is another pict of what I had shown. I don't think the bushing or receiver should be considered as adding to the strength of the assembly.
 

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Very Good, Boyd, you're very observant

Boyd Allen said:
Al,
It may not be so much about bursting as when one arrives at a tight bolt. A long time ago, I read of a comparison between Remington (1 1/6" tenon) and Winchester (1" tenon) both with belted magnum barrels of the same caliber. It was the the author's experience that the Remington has the higher sticky bolt pressure of the two. Gene is shooting cases that have more taper than the PPC and it may be that it takes more pressure for them to get to a sticky bolt (or not). It will be interesting to see how all of this tracks as more shooters try his system.

One more thing about action thread size, Savage has increased the tenon diameter slightly on some of their later model actions without changing the action diameter. Could this be an option for those that want a slightly larger tenon with an indexing bushing? In combination with a Remington lug style washer that was round and functioned only to increase a standard barrel's shoulder contact (on a glue-in) ,there might be some slight advantage.
Click to expand...


Very good Boyd; all good points. :cool: :D

You missed your calling my friend; you should have been an engineer. :)

Later,

Gene Beggs
 
Lesson

Easiest thing to figure out is the hoop stress. Use .221 for ppc inside radius and .500 radius for id of threads on 1.0625 barrel. Plug numbers into this website and look at stresses, highest on inner radius.

http://www.engineeringtoolbox.com/stress-thick-walled-tube-d_949.html

With 60,000psi you get about 90,000 psi hoop stress at 1.0 inch diameter ( 1.0625 thread).
With 60,000psi you get about 113,000 psi hoop stress at 0.8 inch diameter (0.875 thread).

go to http://www.kalyanicarpenter.com/416ss.htm and look up properties.

Most barrels are in the Rc28 range which has a yield at 105,000 psi and a ultimate at 130,000 psi. The 416R is a little better material, but close enough for this calculation.

Yield is less an issue then the ultimate, but it is good to stay below either way. I doubt that in the few thousand cycles that a barrel sees it would be an issue, especially at the short pressure times. I would say that a 7/8 - 28 tpi would be ok.

You can look at the numbers and make up your own mind though. Now you can be an engineer too. :D

PS.. The extra sleeve and action all tightened up on the barrel will add strength for bursting for sure, may not keep the inner stress cracking away if it ever happens though. I think it would take thousands of cycles (shots) to cause cyclic fatigue on the inner chamber.

ps2, alinwa my head is not that big :cool:
 
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Boyd Allen said:
Al,
It may not be so much about bursting as when one arrives at a tight bolt. A long time ago, I read of a comparison between Remington (1 1/6" tenon) and Winchester (1" tenon) both with belted magnum barrels of the same caliber. It was the the author's experience that the Remington has the higher sticky bolt pressure of the two. Gene is shooting cases that have more taper than the PPC and it may be that it takes more pressure for them to get to a sticky bolt (or not). It will be interesting to see how all of this tracks as more shooters try his system.

One more thing about action thread size, Savage has increased the tenon diameter slightly on some of their later model actions without changing the action diameter. Could this be an option for those that want a slightly larger tenon with an indexing bushing? In combination with a Remington lug style washer that was round and functioned only to increase a standard barrel's shoulder contact (on a glue-in) ,there might be some slight advantage.
Click to expand...


Agreed.

I've fought sticky extraction w/factory tenons. I've called it "action flex" but in reality it's probably more related to tenon diameter than anything. I've believed that a Rem with a blocked magwell would take more pressure without getting sticky but this could just be poor observation of limited testing. I've not rigorously tested to find yielding of the lower lug abutment.

al
 
what

that analysis does show is quite a bit more stress which also means quite a bit more strain, ie expansion of chamber. That could easily become sticky brass for extraction.
 
Originally Posted by Boyd Allen
"Savage has increased the tenon diameter slightly on some of their later model actions without changing the action diameter."

Do you think this was done to accomodate the short fat family of cartridges?

I think that maintaining a factor of safety at the tenon is paramount.

For this reason, I would shy away from a fat cartridge in a standard action.

I'm sure some have noticed Ruger's recent entry (RCMs), and their barrels chambers being held to standard mag diameters. They must have some reasoning behind this.

I believe Jerry Sharrett is right on, concerning initial barrel setup being all important.
 
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Chamber strength

It was posted that: Yield is less an issue then the ultimate
I take this to mean it may not be too critical if a barrel yields but is important that it not burst. This makes sense from a safety standpoint but it's not good thinking from a functional standpoint. Bursting thru the receiver section is probably unlikely but yielding might occur if pressure is high enough. Enough people have posted that it should be clear the barrel in the chamber area is going to be stressed up to about 80 - 90% of yield. (With some barrels we would be at yield!) Shooters probably aren't going to blow anything up but they might stretch something!
 
What I meant by that

was that it may not be much of an issue for safety. This whole analysis is very conservative by the nature of it being a very short time event, similar to a vibration or shock event. There is also no case adding in here taking any load, which it does some. Typically the surface may microyield at a point, but will always come back due to the material backing it not yielding. After millions of cycles, the inside surface may see surface cracking and then it would become an issue due to cyclic fatigue, but we will never get there in the number of rounds we shoot. Overall I would not design anything that way, but I also wouldnt hesitate to shoot it and see what happens to bolt and case stickyness etc. It may build residual stress into that inner ring of metal though, I doubt it will really matter.
 
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