Wildcatting / Bolt Thrust?

[wookie76]

Allow me to ramble on a bit.

How do you account for bolt thrust in a single shot where there is no bolt?  This is in regards to barrel stubbing and unconventional or wildcat chamberings.

For example:
HeWhoCan'tBeNamed replied to an inquiry of mine that the 376 Steyr wouldn't be acceptable loading because it operated at too high of pressures. 

Given the known chambering of 270 Winchester and it's .473 case head operating at 65000 psi, using πR² and the Steyr case head of .496, I converted to get a max pressure of 59100 psi.  Several mainstream loading on the Hodgdon data site fall below this.

HeWhoCan'tBeNamed also declines to chamber in 260Rem claiming it also operates at too high of pressure.

[quickdtoo]

Sounds like someone doesn't know what he's talking about, the 260 Rem works fine in a Handi, I have one, it's no different than a 7mm-08 or 308 Win!   The Steyr has a .501"- .506" case head, rim diameter doesn't matter, but it's not suitable for a Handi, maybe if they ever make the Handi-mags someday.

Tim

http://stevespages.com/page8d.htm

http://ammoguide.com/?catid=158

http://www.riflebarrels.com/articles/custom_actions/bolt_lug_strength.htm

Bolt Thrust

Bolt thrust is easy to calculate. Only two inputs are required. They are peak chamber pressure in PSI and as mentioned, the inside area of the case head that the gas pressure can work on. The formula then is:

THRUST=AREA*CPSI Where:

AREA=3.1416*(HS/2)^2

HS=the diameter of the inside of the case head.

[trotterlg]

Well, it isn't the inside of the case head, it is the entire diameter of the case head not including the rim if there is one.  The pressure can act on the diameter of the chamber just like the piston in an engine does.  There may be some reduction in the loads because of the brass not moving freely inside the chamber, but they are not easily defined so just go the the chamber diameter at the breach and be safe.  The standing breach is exactly the same as the bolt, they both see the same loads.  I don't know what you are really asking for?  Larry

[quickdtoo]

Bolt/breech thrust is calculated using the pressure and the INSIDE CASE HEAD AREA, not the chamber diameter, I already posted one source for the formula, here's another.

Tim

http://en.wikipedia.org/wiki/Bolt_thrust

Calculating bolt thrust

With a basic calculation the bolt thrust produced by a particular firearms cartridge can be calculated fairly accurately.
[edit] Formula

    \vec{F_{bolt}} = P_{max} \cdot A_{internal}. [1]

where:

    * Fbolt = the amount of bolt thrust
    * Pmax = the maximum (peak) chamber pressure of the firearms cartridg
    * Ainternal = the inside area (of the cartridge case head) that the propellant gas pressure acts against

Cartridge case heads and chambers are generally circular. The area enclosed by a circle is:

    Area = \pi r^2 \approx 3{.}1416 \cdot r^2.

where:

    * π ≈ 3.1416
    * r = the radius of the circle

Equivalently, denoting the diameter of the circle by d.

    Area = \frac{\pi d^2}{4} \approx 0{.}7854 \cdot d^2.

The green line denotes the internal case head diameter and the red line the external case head base diameter of a rifle cartridge case.

A practical problem regarding this method is that the internal case head diameter of a particular production lot of cartridge cases (different brands and lots normally differ dimensionally) can not be easily measured without damaging them.

[McDerry]

Tim beat me to it.

Bolt thrust is the force exerted back on the breech face.

It is the inside diamter of the case head though, as the case is functioning as a pressurized bladder versus a piston.  Essentially backwards of how a piston would function.

Can use the outside surface area for ease of calculating just remember it will only be a ball park figure then.

Suprisingly a a 12 gauge (7700# of bolt thrust)  makes the .223 Remington (5500# of bolt thrust) look like a powder puff bolt thrust wise.  


Mind you your math about the steyr pressure being reduced is slightly flawed.  Its already being expressesd in psi so there is no need to try to calculate a new chamber pressure.  It is still going to be 60,000psi cartridge.  The problem is it will be producing in excess of 12250 pounds of bolt thrust.  a 270 winchester is producing 9000 pounds bolt thrust tops.

[quickdtoo]

Suprisingly a a 12 gauge (7700# of bolt thrust)  

I get 3584 lbs thrust using an actual .630" inside diameter of a 12ga case I just dissected which is far more realistic considering the SB1 frame they come on. 

Tim

[wookie76]

I was scheme'n and dream'n a 376 Steyr Flanged wildcat based on it's parent.
http://triebel-shop.com/product_info.php?cPath=240_380_488&products_id=26212&osCsid=33435271442d2d12e8559d46bb5e9594

[trotterlg]

Sorry Quick, you are wrong on this one.  If we were to take your exapmple to an extreme, if you had a case head that had an inside shape that tapered to zero at the primer flash hole your formula would have zero breach thrust.  We all know that would not be true.  This is exactly like any piston in any cylinder, the total thrust is calculated using the area of the cylinder and has nothing to do with the shape of the piston in it.  Larry

[quickdtoo]

I was scheme'n and dream'n a 376 Steyr Flanged wildcat based on it's parent.
http://triebel-shop.com/product_info.php?cPath=240_380_488&products_id=26212&osCsid=33435271442d2d12e8559d46bb5e9594

You could always run it at reduced load capacity, but I tried that with a 300WSM barrel hoping to at least achieve 30-06 Ackley velocities, I barely made standard 30-06 velocities with 150gr moly bullets, the larger case head just isn't Handi friendly, just too much flex within the action. 

Tim

[quickdtoo]

Sorry Quick, you are wrong on this one.  If we were to take your exapmple to an extreme, if you had a case head that had an inside shape that tapered to zero at the primer flash hole your formula would have zero breach thrust.  We all know that would not be true.  This is exactly like any piston in any cylinder, the total thrust is calculated using the area of the cylinder and has nothing to do with the shape of the piston in it.  Larry

I think you need to read the links I posted Larry, then write Dan Lilja and Al Harral and tell them they're wrong too, Harral spent 30yrs at Lawrence Livermore as a structural engineer for crying out loud!!    

Tim

http://www.varmintal.net/abolt.htm

http://www.varmintal.net/index.htm

[tykempster]

trotter, the inside area is what you are dividing by, therefore if the inside of the case head approaches 0, you're dividing by a small number, giving you astronomical bolt thrust.

At least that's how I'm reading it...(something/something(casehead))

[McDerry]

Suprisingly a a 12 gauge (7700# of bolt thrust)  

I get 3584 lbs thrust using an actual .630" inside diameter of a 12ga case I just dissected which is far more realistic considering the SB1 frame they come on. 

Tim

Can't be smaller then .730 (bore size) and that leaves you with over .085 of material, think federal cartridge  Thats 5229 lbs at 12500 psi.  Jump that up to the pressure limits on some of the magnumn imports and your pushing the high 7's.   Measuring inside the web of the case defeats the purpose of taking the inside measurement.

[quickdtoo]

The SAAMI MAP for the 12ga is 11.5 kpsi, and as I stated, .630" is the actual measured inside diameter of a Winchester 2¾" hull where the powder rests, 12ga 3½" Mag would be a bit higher with a SAAMI MAP of 14kpsi, thrust would be 4364 lbs. I think I have some 3½" mag hulls, I'll dissect one and check it out later.

Tim

http://www.leverguns.com/articles/saami_pressures.htm

[gcrank1]

As this is another element of chamber pressures I will post it here for consideration:
I understand that a pressure vessel; ie, the case will also have twice the radial pressure (to the case walls) than to the ends (one, the breech thrust, the other the ejecta).
The ejecta, since it is movable will have an varying effect by whatever its weight is, once the stable inertia is overcome.
The case wall/chamber friction outward will slow or reduce the breech thrust somewhat.
Since we cant measure or calc these for every given situation we go with the 'rule of thumb' calc's to give a ballpark.
For any cartridge that will even approach the upper limits of safety in these rifles I shy away.
I keep remembering the admonition that at some point these may become a 'pipe bomb'.

[McDerry]

The SAAMI MAP for the 12ga is 11.5 kpsi, and as I stated, .630" is the actual measured inside diameter of a Winchester 2¾" hull where the powder rests, 12ga 3½" Mag would be a bit higher with a SAAMI MAP of 14kpsi, thrust would be 4364 lbs. I think I have some 3½" mag hulls, I'll dissect one and check it out later.

Tim

http://www.leverguns.com/articles/saami_pressures.htm

Tim its not where the powder rest that is important its the largest diameter of the inside of the case head.  As soon as the case goes from the straight wall to the web that tapers to the primer pocket is where you should be measuring.  It can't be decreased below bore diamater.

Also don't forget proof pressures and bolt flex when comparing the two recievers.

[quickdtoo]

I found a 3½" hull, inside case head ID is .707" that equates to 5511 lbs thrust at 14kpsi.

Tim

[tykempster]

Of course it could be decreased below bore diameter, that's why a bullet won't seat all the way down to the case head in a straight walled case, as a primitive example...or else you'd be dealing with cases that were not any stronger just in front of the web than at the "neck".

[Shu]

If you can't do the 376 styer try the 375/444. It is pretty close to the same balistics.
I have a 376 styer built on a mauser 98, you know when you shoot it. Recoils is not bad, but I kinda shudder a bit thinking about it on a handi.

Good luck with your pursuits.