handi breech thrust question

[Jason F]

Where is a good source to look up breech thrust to see what is capable to be used on Sb1 frames

[keith44]

that information is locked away in the archives of the original R&D dept of H&R.  If they actually designed it, otherwise it is in the secret archives of the firm that actually designed the first SB1 and performed the destruction tests.  Most of the time this is not available to anyone outside of the R&D group, and perhaps a few engineers tasked with lowering production costs.

[trotterlg]

The SB-1 problem isn't so much the breach thrust as it is the forward thrust on the barrel.  Straight walled cartridges have very little forward thrust because there is no (or not much) area of the case for the pressure to act on.  With a bottel neck case the pressure acts on the area of the sholder of the cartridge which produces the forward thrust on the barrel and therefore on the frame.  The other problem is the area that the breach thrust acts on, they can stand a lot of breach thrust if it is spread over the area of a 12 gauge shell, but consentrate that same amount of thrust on the area of a .223 case head and there is a problem.  Good luck, don't shoot your eye out ;^)  Larry

[necchi]

a lot of breach thrust if it is spread over the area of a 12 gauge shell, but consentrate that same amount of thrust on the area of a .223 case head and there is a problem.

And that's the key right there Jason. There's a huge difference when you put that pressure into an area of .378 like the 223 or the .473 of a 30-06.
Tim showed a calculator for pressure and area a time or two but I can't remeber the thread

[otterbob]

Jason F

As already stated, it is a secret !
However you can get a good idea by compairing what has been done and what is being done.

Breach Force was discussed just a week or two ago, Here is the comments I posted on that thread.

"Vacek,

I am not here to argue with the “experts” on the forum, but here are a few interesting numbers.

As posted above 40,000 psi calibers are being “considered” safe by many members.
Yet they also throw in breech force as a variable that must be considered.

Using the formula posted here on the forum for breech force and rounding off , these are the numbers I get.

Your 22 Hornet = 2999
Your 223 = 6075
Some of the other calibers and gauges that appear on an SB1 and or pre SB1 frame :
30-30 = 5875
44 Mag = 5902
45-70 (28,000) = 5608
12ga 3 inch = 5999
12ga 3 ½ inch (SB1)= 7304
*** 45-70 (40,000) = 10,100

As you can see the 12ga 3 ½ inch breech force far exceeds your 223 on the same frame, it is only my opinion that if the barrel can handle the chamber pressure then the action should not have a problem with the “breech force”.

As for the interesting “*** 45-70 (40,000) = 10,100” see the article in the link below
http://www.realguns.com/Commentary/comar52.htm
Please note that the article is concerning lever guns but lists heavy bolt actions and single shots as having stronger actions.

Run the numbers for yourself and make your own decision.

Most barrel steel produced is formulated and heat treated for 100,000 psi or higher and heat treated to 25 - 32 Rockwell C. What H&R has done in the past and present is a secret, that is why all we can do is compare what has been done and what is being done on what frame in order to make an educated judgement."




Otter Bob

[otterbob]

a lot of breach thrust if it is spread over the area of a 12 gauge shell, but consentrate that same amount of thrust on the area of a .223 case head and there is a problem.

Breach Thrust is a calculation that "INCLUDES" the diameter of the case at the head as a variable. Unless there is another calculation being offered, which I would like for my own information, breach thrust remains breach thrust for which the iron/steel must be formulated and treated to handle.


Otter Bob

[trotterlg]

It is the area that the breach thrust is applied to, like hitting a center punch with a hammer, small area of the pointy punch puts a dent in what the punch is resting on, Strike something the size of a Quarter with the same hammer and there is no dent.  This is not rocket science.  Larry

[ibgp3]

..............................................................
                         223 = 6075
..............................................................
12ga 3 ½ inch (SB1)= 7304
...............................................................

As you can see the 12ga 3 ½ inch breech force far exceeds your 223 on the same frame, it is only my opinion that if the barrel can handle the chamber pressure then the action should not have a problem with the “breech force”.
...............................................................


Otter Bob

I always assumed the .223 was excluded because of the .556 loads with much higher pressure.


...also, as someone pointed out above, Breech thrust is not strictly equal to the piston force calculated on the base of the cartridge. Shoulder thrust adds a component and chamber friction subtracts a component, to mention two.


I recall a story about P O Ackley demonstrating the advantage of straight walled cases by firing a rifle without the bolt.  I haven't ever read any article on that, so it may be a legend.

[keith44]

I recall a story about P O Ackley demonstrating the advantage of straight walled cases by firing a rifle without the bolt.  I haven't ever read any article on that, so it may be a legend.

I do not recall that one, and have read just about everything I could find by P.O. Ackley.  He may have done it though,  I just do not remember that...

[necchi]

Run the numbers for yourself and make your own decision.

Ther's not a snowballs chance in a hot place I'd even consider that.
 
There's a reason the makers aren't doing it and haveing the frame fail isn't a secret, it's fact.
 
H&R knows what their doing and their not going to take a chance on a law suit because a gun blows up.
 
It's not some secret way of making more money because they can make folks buy another frame,
,It's plain and simple about saftey.
 
What are you doing here with that statement OtterBob? Trying to somehow say it's OK to put high pressure barrels on a low pressure frame? And a guy should try it for himself because the company is withholding info or data?

[OldSchoolRanger]

Jason,
 
 Don't know if this will help, but there was a discussion recently regarding this same subject just worded differently.  I posted the links for you.
 
 http://www.gboreloaded.com/forums/index.php/topic,244542.0.html
 
 http://www.gboreloaded.com/forums/index.php/topic,246776.msg1099429269.html#msg1099429269
 
 http://www.gboreloaded.com/forums/index.php/topic,247161.msg1099431801.html#msg1099431801
 

[Swampman]

The breech thrust for a bottle necked cartridge is different than that of a straight walled cartridge all else being equal.  A longer cartridge will have less breech thrust than a short one all else being equal.

[otterbob]

 
 
Breach Thrust calculates thrust against the face of the bolt. Thus the bolt lugs must be strong enough to handle the thrust. The handi has no bolt lugs , instead it uses a solid mass as an integral part of the frame to withstand the thrust created when the cartridge fires. To say that there is a difference in thrust created by a small center-fire cartridge verses a large center-fire cartridge is correct by default, but to say the amount of thrust created by the “shape” of the cartridge as a factor would mean you are using a different formula by default , as shape is not a variable in the bolt thrust equation.

 
H&R 1871 has determined that the stress applied to an SB1 frame cannot exceed “****” and the same determination has been made for the SB2 frames. What “****” is, they will not divulge. However we the users that modify a “Handi” make judgements based on known formulas and known pressures that we can derive from what is being done and what has been done.

 
Now if you do not think that a 12ga 3 ½ inch mag does not produce more breach thrust then a 223 rem then produce your formula/equation so that we can “peer review” the numbers to test your  formula/equation.

 
I know that many of the readers here are going to cringe when they read this next statement, And they have the absolute right to do so.

 
THE FOLLOWING IS MY OPINION !!!

I WILL NOT TELL ANYONE WHAT CAN OR CANNOT BE DONE TO A HANDI !!!


Considering that the factory would not “push the envelope” I will stand up and say that in my best judgment the SB1 should be a 10,000 psi frame and the SB2 would be much higher.

 
Otter Bob

 

 

[Swampman]

The amount of cartridge case touching (gripping) the chamber walls and it's shape effects how it grips the chamber and thus how much thrust there is.  This is one of the reasons it's important not to have lube on the case or oil in the chamber.

[BAGTIC]

Depending on cartridge case friction to restrain chamber pressures is extremely unwise. Cartridge cases vary in strength, ductility, friction coefficient. Any effect case friction has in confining bolt thrust should be considered a bonus and not something on which to depend.
Consider that cases occasionally split or separate. When that happens the interior of the case ceases to be the 'piston' against which the gas pressure exerts it force. The diameter of the interior of the chamber itself  becomes the limiting factor. A prudent person would calculate breech thrust based on chamber diameter itself as a contingency against unanticipated case failure.
If the case is gripping the chamber walls then any setback of the lugs, even though temporary, will result in case stretching which can result in thinning of the case walls just forward of the head. This is the cause of many of the bright rings visible on the outside of overworked cases and the grooves that can sometime be detected on the inside of the case with a paperclip or other probe. It is also why in some countries proof loads are well lubricated before firing in order to assess worst possible case  head thrust. Plan for the worst possible scenario, hope for the best.

[trotterlg]

This is very much correct.  On a Handi you also need to consider the forward thrust on the hinge pin.  This is mostly from bottel neck cases and the forward thrust against the sholder of the cartridge.  It is easy to calculate, straight walled cases only exert a forward thrust eqiuvelent to the friction of the bullet going down the barrel, while the chamber pressure acts on the sholder area of a bottle neck case to push the barrel forward.  I guess the loads on the frames are a lot more complex than most people think.  Larry

[necchi]

Yeah, there is alot going on.
 
I understand Otter Bob's point, he spelled it out plainly, but I'm sure glad determining what barrel goes on what frames is determined by someone elses best judgement.
 
I've seen first hand too many times what happens when someone poo-poo's the safty standards and pushes the envelope with guns and loading cartridges for them.
 
 There's been more than just a few sad stories posted on this forum and others here on GB's alone.

[otterbob]

On a Handi you also need to consider the forward thrust on the hinge pin.  This is mostly from bottle neck cases and the forward thrust against the shoulder of the cartridge.  It is easy to calculate,  Larry

  I would enjoy seeing your simple equation for forward thrust, Please post it when you get the chance.

 
IF there is forward thrust as you state, it would be negated by breach thrust by an equal factor (newton's laws not mine) therefore allowing us to increase the breach force factor equivalent to the forward thrust factor allowing even more range of breach thrust and the possibility of more chamberings.

 
For forward thrust to increase pressure on the frame hinge pin it would have to be in excess of breach thrust ( again, newton's laws not mine).

 
The different shoulders angles of a bottleneck cases will change the timing of the pressure application of breach force by a minuscule amount.


PS:  members of the forum,
Although it appears at times we (some members) are attacking one another for their point of view, I wish to say that most of us are just strongly presenting our points of view. As for myself I still enjoy the posts of the members that I sometimes quote.
This is a forum where we have been allowed to state our positions with a passion without having to flame another's.
 

 
Otter Bob
 

[ibgp3]

"Forward thrust":

Sometimes extreme examples make concepts clearer.
In the .44 case at the top, "forward thrust" is easy, it equals 0.
In the second case, the .44 is necked down to .22; but because it is bottle necked, calculation and visualization of the effect of the pressure on the rifle is difficult.
In the third case the barrel has a 44 chamber and no outlet. (Don't try this at home ;>)
Calculation of the "forward thrust" is easy: it equals the piston thrust at the back of the case.
Does the "forward thrust" cancel the piston thrust? Nope, sorry, they combine; just as they do in a bottle necked case.
So the "forward thrust" is just part of the breech thrust.

[trotterlg]

I am so glad to see some one besides me gets this!  Larry

[Swampman]

I get it....I studied it about 30 years ago.

[otterbob]

Does the "forward thrust" cancel the piston thrust? Nope, sorry, they combine; just as they do in a bottle necked case.

If you mean that one cancels part of the other, then you are correct.

So the "forward thrust" is just part of the breech thrust.

Not possible by the laws of physics, You can not move forward and backwards at the same moment in time. You can ADJUST the amount of movement of the other by an increase or decrease in the thrust of the opposite. if you combine forward thrust with a greater reverse thrust then you have canceled the forward thrust by using an equal amount of the reverse thrust thus reducing the reverse thrust with a lesser forward thrust.


If anyone wishes to discount or include a variable to the breach force equation as found posted here on the forum then I say again, post your equation so that we can review it.


Otter Bob

[trotterlg]

You got a mouse in your pocket?  Larry