New Handi specific Magnum cartridge design safe for SB1 frames!

[trotterlg]

I've finally found the solution to shooting High pressure rounds on any H&R frame.  Secret it is the design of the cartridge base and inside of the brass.  In the design below, the cartridge operates at 65,000 PSI however the breach thrust is only 1,600 pounds due to the diameter of the inside of the brass at the case head.  By reducing the inside of the brass to .175 inches at the case head the pressure acts on only .025 Square inches reducing the breach thrust to about what a 22 Mag produces.  Really cool right guys?  Larry




How many of you believe this is true? 

[nomosendero]

All things considered I thing I will go the cheaper route & continue to buy bolt guns that will handle the cartridges I
want to shoot & even do it accurately. 

[26-t]

Way to GO!! This could be the way of the future. You have my vote. Thanks 26-t

[Matt3357]

I could be wrong, I was once a long time ago, but if you have the same amount of thrust but reduce the area you still have the same amount of thrust but at dangerous levels of concentration?  In other words, wouldn't it blow primers and possibly pierce your frame? Seems an awful lot like a nozzle to me.

Matt

[trotterlg]

Move down to the "wildcat /breach thrust" string, Quick Says this is how it is calculated. 

[trotterlg]

In case you haven't figured it out, I really don't believe this for a half a second.  Lary

[Matt3357]

Good deal,  I was hoping I caught your drift.  Sometimes it is hard to tell the tone through text. 

Matt

[quickdtoo]

Move down to the "wildcat /breach thrust" string, Quick Says this is how it is calculated.  

The professionals below are the ones that state how breech/bolt force is calculated.


Here's the supporting documentation for the bolt thrust formula that Larry is challenging, the first is by Dan Lilja of Lilja Precision Rifle Barrels, Inc.

Tim

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

Bolt Thrust (By Dan Lilja  )

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.

Here are the same two factors for calculating bolt thrust by Anthony G Williams which agree with the Lilja formula, this fella has some substantial credentials. http://www.quarry.nildram.co.uk/

http://www.quarry.nildram.co.uk/ballistics.htm

One cartridge issue affecting gun design is bolt thrust. This is the rearwards push on the gun's bolt or breechblock caused by the cartridge firing. This depends on two factors: the chamber pressure, and the inside diameter of the base of the cartridge case. Put simply, the wider the cartridge case, the greater the surface area the pressure has to work on, so the greater the bolt thrust for any given chamber pressure. So a long thin cartridge case may develop the same chamber pressure as a short fat one with double the internal base area, but the latter will develop double the bolt thrust. The greater the bolt thrust, the stronger the gun's locking mechanism has to be to withstand it.

And another from Realguns with calculated breech face pressures for several levergun chamberings, note that he states the source as Dan Lilja and adds the specific criteria of the area of the smallest interior surface of the case web perpendicular to the bore.

Some things I don't know about bolt thrust....

Lately, bolt thrust seems to come up whenever there is discussion about the pressure handling characteristics of a particular firearm and cartridge combinations, i.e. "You can rebarrel your Chipmunk and make the change from .22 Hornet to .577 N.E., but beware of the increased bolt thrust". Why be concerned about bolt thrust at all ? Forget those giant 2 or 3 or 9 or more bolt action lugs, or even that rotating lock up of a Savage or Browning lever gun. The Marlin has basically three small pieces of metal holding that bolt in place behind the cartridge, maybe 3/8" thick at the widest point and thinning dramatically behind the forward "lug" on the lever. I guess I can include the pivot screw that holds the lever in position as part of the overall support equation.

Bolt thrust is one of those firearm strength indicators, or probably more correctly stated, forces working against strength indicators, that is of little use without knowing the strength of resistance. Without a baseline to define acceptable or excessive thrust, there is little significance in the indicator ?

Most recently I've seen the formula for bolt thrust expressed as being equal to the area of the smallest interior surface of the case web perpendicular to the bore, multiplied by the chamber pressure, and expressed as p.s.i1. This is similar to determining the compression strength of a column by calculating at the smallest diameter, but I don't believe this can be expressed as p.s.i because bolt thrust is suppose to be an aggregate pressure exerted over an area, the surface area at the case web perpendicular to the bore. As a relative indicator it works pretty well. I arrived at a radius by dividing the interior case diameter by two, I squared the result and multiplied by 3.14 to get the surface area. I multiplied the area by the case pressure and expressed the result as pounds of breech face pressure. In any event, the following table represents some relative measurement across several of the chambers available for this gun.

Marlin Cartridges - Big Bore or 336 Versions
Cartridge    Chamber Pressure     Lbs.\Breech Face Pressure    % +/- .45-70 SAAMI
.30-30              42,000                     5278                             +2%
.35 Remington       33,500                     5002                                  -3%
.44 Magnum          36,000                     5252                                  +2%
.444 Marlin          42,000                7287                            +41%
.45-70 SAAMI       28,000                     5152    
.45-70                   40,000                 7359                             +43%
.45-70                   45,000                 8279                             +61%
450 Marlin             51,500                 9475                             +84%

Footnotes: 1. Lilja Precision Rifle Barrels

[McDerry]

Based on the drawing you would be measuring the cases interior width at the .500 mark.  Immediately after that is the web of that case. 

[Shu]

And this new cartridge will shoot a 200 grain bullet at 8000 fps so I have no hold over out to 1 mile, no recoil and be silent so I won't ruin my hearing. Maybe I should think about replacing my 45-70. 

There are some calculations that give an inverse answer after a certain point. In a rocket motor the burn rate/nozzle size vs. pressure caculation does this. I don't fully understand it but it does.

[bikerbeans]

Dang!  Now you guys tell me it's a joke after I already ordered the reamer from 4D.

BB

[mrbgt]

I might need a bigger reloading press or at least a 4 foot breaker bar to size the brass 

[MSP Ret]

You guys are all missing Larry's point. This is only the parent cartridge. I am interested in buying a .17 HMR or .17 Mach2 barrel, fitting it to an SB1 frame and having it rechambered from the parent cartridge (the .308 trotterlg Super Special), to the ".308 trotterlg Super Special/MSP Ret .17 Highstepper AI".
This would be eaily accomplished by simply necking down the parent cartridge to .17 caliber, an easy one step process, then fireforming it to AI. With the reduced pressures there would be no problem with the SB1 reciever or the steel used for the rimfire barrel. I can see it with either a ghost ring aperture rear sight or a large diameter Red Dot for fast close range target engagement....Merry CHRISTmas to all....<><....

Oh, one thing I forgot, an ammo cuff on the buttstock for fast reloads when hunting dangerous game...  

[gcrank1]

Im thinking a 12ga. USH with a .17 cal. liner, using modified 50BMG brass with a turned powder chamber inserted before necking down. Should be good for 'ludicrous speed' !
BTW, that diagram reminds me of a shaped charge.........

[Shu]

Yes it does look alot like a shaped charge... well the forming part anyway. With this drawing there can be very little pressure on the primer. I think it's a winner. Too bad I won't get the credit or the royalties...

[manatee1947]

So this is the antithesis of the WSSM, therefore , say a 204 Ruger, and a 9.3 X 74R are excellent Handi choices ? Therfore the ultimate Maxi- if I may, would be a 357 case extended to 3.8 inches and necked down to .257 diameter, thereby producing a 25666666666 winchester ??

[gcrank1]

Larry, I believe you have 'created', quite literally, a monster..........

[jedman]

    Great Idea !    I would think the cases could be made from inexpensive plastic and after firing you just discard them.  

    Merry Christmas  !!