Rimmed and Rimless, Case Capy in Theory

[TomkinsSP]

So, in my time on this forum I see debates as to the relative power of longer rimmed and shorter rimless cartriges that load the same diameter bullets. As someone who does not have an education in math or physics, but has been reloading 15 years now, and sees the debate as comical, I wonder if I am missing something.
As everyone on this forum knows, both the .37 Pike-Carson and the 9.5mm Junkers use .371 bullets nominally 175 grains. Conviently the case capacity of the .37 P-C is exactly twice that of the 9.5 J with fully seated 175gr projectiles. SAAMY rates the .37 at 16,000 ZUP and the 9.5 at 32,000. I use 4.0 grains of PolkaDot in both loadings. PolkaDot is the worlds fastest powder so it burns instantaneously in the case, and the pressure spike is at ignition.
My contention is that because there is twice as much space in the .37 P-C brass as in the 9.5 J brass, the pressure is halved.
Data in Pettigrew's 3d ed, and real word experience with firearms of similar barrel length seem to support this idea.
Am I crazy, lucky, both?

 

[Engineer1911]

Your posts are lacking spelling, content, and fail to ask a valid question.


Capy and Minty: Two incredible terms used when describing firearms.

Case capacity vs powder burn rate and charge is addressed in a reloading manual.

 

[Rule3]

It will make perfect sense to some folks!

 

[scooter123]

Actually if you ignore the mis-spellings, grammar errors and concentrate on the "gist" of what he is expressing it is a near text book example of Boyle's Gas Law. So what he has expressed not only makes perfect sense it's also well supported by Proven Physics. Basically if you take a particular Mass of a gas and reduce the volume containing that Mass of Gas by One Half the pressure of that gas will Double.

PS; what I haven't mentioned is the effect of temperature in Boyle's Law but because he didn't mention a change in the Temperature in his example we can simply ignore that aspect in this case. Basically in this simplification we limit the equation to P1V1 = P2V2. If anyone really wants to get Fussy Boyle's Law is fully expressed as PV=nRT.

 

[TomkinsSP]

You posts are lacking spelling, content, and fail to ask a valid question.

I smell very well, use old spice and everything.

 

[Nevada Ed]

Do you shot these rounds............?
or is this a general question ?

A picture of the weapon would be GREAT !!

 

[ImprovedModel56Fan]

Am I crazy, lucky, both?

Yes. Why do you ask?

 

[Warren Sear]

You posts are lacking spelling, content, and fail to ask a valid question.

On top of that, he started his post with the word "so". Definite fail.

 

[TomkinsSP]

I can't because they don't exist.

Moving to the less imaginary world of .38 S&W special, 9x19, and .357 rem mag, what prompted me to post were several posts that said something similar to "I moved from .38 spl to 9mm because I can shoot a more powerful round in 9mm."

My shelf here has .38 and .357 loaded ammunition comprised of TB, 231, 700x, BE, PP, TG, LS, 2400 under 75, 90, 100, 115, 125, 140, 148, 150, 158, 160, 180 and 195 grain boolits. I have some CSB-1 and Solo1000 and 225 grain 'pencils' I haven't tried yet. I have some 9x19 loaded ammunition of 100, 125, 147, 150 grains over 2400, TG, BE, 231.

In my limited experience with 9x19 (only have a 940 chambered in 9x19, but have identical 40 in .38 and 640 in .357), ole' Boyle was on to something.

Loaded with 150 grain boolits, which seem to take up the equivelent of 7.0 gr of water, my 9x19 has room for 6.3 grains of water under that boolit, my .38 has room for 17 grains and my .357 has room for 20 grains. So using SAAMI standards...

CART capy -7.0 allowable pressure
9x19 13.3 6.3 330 cup/100 +p 393 cup/100
.38spl 24.0 17.0 170 cup/100 +p 200 cup/100
.357 27.0 20.0 450 cup/100

Since the .38 has 2.69 times the space under the boolit, to handle 0.51 times the pressure, I can obviously SAFELY load this particular boolit faster in a .38 than in a 9. I could SAFELY load this particular boolit faster in .38+p than in 9+p. And .357 well, I have 3.17 times the space and can handle 1.14 times the pressure of 9+p, we are talking tall blondes with submachine gun pressure here.

Apples to apples no load I can make for a 940 will beat a load I can make for a 40 let alone a 640.

Your apples may be of a different variety.

 

[TomkinsSP]

And...

So

 

[fredj338]

I can't because they don't exist.

Moving to the less imaginary world of .38 S&W special, 9x19, and .357 rem mag, what prompted me to post were several posts that said something similar to "I moved from .38 spl to 9mm because I can shoot a more powerful round in 9mm."

My shelf here has .38 and .357 loaded ammunition comprised of TB, 231, 700x, BE, PP, TG, LS, 2400 under 75, 90, 100, 115, 125, 140, 148, 150, 158, 160, 180 and 195 grain boolits. I have some CSB-1 and Solo1000 and 225 grain 'pencils' I haven't tried yet. I have some 9x19 loaded ammunition of 100, 125, 147, 150 grains over 2400, TG, BE, 231.

In my limited experience with 9x19 (only have a 940 chambered in 9x19, but have identical 40 in .38 and 640 in .357), ole' Boyle was on to something.

Loaded with 150 grain boolits, which seem to take up the equivelent of 7.0 gr of water, my 9x19 has room for 6.3 grains of water under that boolit, my .38 has room for 17 grains and my .357 has room for 20 grains. So using SAAMI standards...

CART capy -7.0 allowable pressure
9x19 13.3 6.3 330 cup/100 +p 393 cup/100
.38spl 24.0 17.0 170 cup/100 +p 200 cup/100
.357 27.0 20.0 450 cup/100

Since the .38 has 2.69 times the space under the boolit, to handle 0.51 times the pressure, I can obviously SAFELY load this particular boolit faster in a .38 than in a 9. I could SAFELY load this particular boolit faster in .38+p than in 9+p. And .357 well, I have 3.17 times the space and can handle 1.14 times the pressure of 9+p, we are talking tall blondes with submachine gun pressure here.

Apples to apples no load I can make for a 940 will beat a load I can make for a 40 let alone a 640.

Your apples may be of a different variety.

You are making too many simple assumptions. One thing i have learned in more than 40yrs reloading, pressures are rarely linear, start peaking at diff points depending on bullet wt & volume & burn rate within a given case volume. So you cant take pressures from one totally diff cartridge & extrapolate to another with any degree of accuracy. IT will always be a WAG.

 

[forestswin]

Your posts are lacking spelling, content, and fail to ask a valid question.

Fixed it for you

Added an 'r' to you....spelling

And

I don't have my physics book handy, but if I remember correctly
You can divide your imaginary numbers by the imaginary unit (i)
To get real numbers

 

[hdwhit]

scooter123 wrote:
...a near text book example of Boyle's Gas Law. ... in this simplification we limit the equation to P1V1 = P2V2.

If anyone really wants to get Fussy Boyle's Law is fully expressed as PV=nRT.

I have no argument with what you wrote, scooter123. If we ignore Temperature when applying Boyle's Law, then doubling the volume does indeed halve the pressure (or vice versa).

It is also a purely academic result that is meaningless in practice since:

1. Combustion of the powder is a vigorously exothermal reaction so in this case the change in temperature is a material factor in the application of Boyle's Law,
2. Combustion does not take place in zero time, and
3. Once time is brought into the understanding of the problem it ceases to be a linear equation as the rate of combustion of most powders is influenced by both the rate of pressure increase and temperature increase.

Thus, while the understanding of the simplified statement of Boyle's Law by TomkinsSP is correct, the simplified statement is not sufficiently representative of what goes on in a cartridge when it is ignited, so the answer to TomkinsSP's question(s) are:

• Your simplifications of the underlying theory make it meaningless in practice and applying it to reloaded cartridges will lead you to erroneous and potentially dangerous conclusions, so to proceed along this line would mean you are crazy.
• Yes, the fact the differences between the theory and practice have so far failed to align in such a way as to damage your guns or maim your person has been sheer luck.

 

[rwsmith]

Don't expect linear relationships.......

One thing you cannot assume in internal ballistics is that changes in variables produce a one to one relationship all through the curve. The powder burns differently in a larger or smaller space, the velocity produced changes the volume of burn area differently. One may burn hotter under those conditions. The curves produced may be similar, but one could be steeper or have a faster rate of climb.

Extrapolation in reloading is risky because of this. If that is all that you have to go on though, make sure that your estimate is conservative.

An example of this is the 9mm case. A .38 bullet is almost the same size but the 9mm case has a fraction of the volume. You can set .38 bullets to any depth you want, but in a 9mm, a slight change of case volume caused by pushing in the bullet a short way can produce drastic rises in pressure.

I haven't looked it up but I would bet that the cartridges you mention have different working pressures, too.

 

[TomkinsSP]

You are making too many simple assumptions. One thing i have learned in more than 40yrs reloading, pressures are rarely linear, start peaking at diff points deoending on bullet wt & volume & burn rate within a given case volume. So you cant take pressures from on totally diff cartridge & extrapolate to another with any degree of accuracy.

What I think that I am seeing is: outide of a case (a) the same single base propellant without carbon added as a retardant has a perfectly linear burn rate. (b) Since combustion starts at the surface, doughnuts, small balls, big balls, sticks, little flakes and big flakes burn at different but consistant rates. Inside of a case: (c) full cases burn better because ignition is more consistant (and yes BE is so much less finicky than TB in this regard), (d) pads or discs can keep smaller loadings tight to the touch hole, replicating the ignition pattern of a full case. In ammunition loaded with THE SAME BULLET BUT IN DIFFERENT CASES e) these observations are most pronounced in loadings where the solid propellant is converted to gas within the case, in loads where some burn is in an identical barrel its pretty similar, but loads where some powder burns outside the barrel it is less similar.

While 75% or more of my experience in loading has been with .38 special. I have a fondness for flat based lead bullets, ones I would call wadcutters or semi wadctters. With similar bullets I have found points of convergence in same weight, similar design lead bullets having either exactly or within a few tenths of a grain charges of the same propellant in .44special/.45acp and .357(rifle)/.30-30/7.62x39.

 

[TomkinsSP]

Maybe I am not expressing this clearly. I am not suggesting that because I can fit 30.0 grains of Kaboom Powder into a .38 special case I would do so. Nor am I suggesting that I could use my bullet-puller, pop a bullet off of a .38 and dump the powder in a nine case, seat the bullet and... (I bet it would be safe to do the opposite, as the greater volume will result in a lower ignition temperature (for exactly the reasons stated) but that is not my intent or plan either.

What i am doing is trying to optimise rounds for snubbies. This isn't magic, IMHO if you control enough variables, its science. And if not linear well it plots along a common parabolic curve.

I am shooting exactly the same projectile, through an identical barrel (640 and 940 are a tad over 2", 40 a tad under), slugged they are too close for my micrometer to tell the difference. Same powder, same charge (which is limited by those short barrels and my desire not to see a ball of flame, otherwise it would be limited by pressure in 9x19 first), roll crimped in the same die.

Now maybe Tim or somebody had some super-secret non canister powder that can somehow elevate 9x19 over .38, but I don't see it in TB, BE, 251, LS, 700x, TG, 2400, at least with a 150grain wadctter.

 

[reddog81]

Them's some very, very confusing posts.... Load data from published sources - USE IT!

Everyone of your posts contains statements that make zero sense.


Re: "Now maybe Tim or somebody had some super-secret non canister powder that can somehow elevate 9x19 over .38, but I don't see it in TB, BE, 251, LS, 700x, TG, 2400, at least with a 150grain wadctter."

Who shoots 150 grn wadcutters in 9mm? What reloading data are you looking at? A quick glance in Lyman #48 has plenty of jacketed 147 grain 9mm loads over 1,000 FPS and 146 grain jacketed bullets in 38 Special top out right around 800 FPS. This is common phenomenon across all bullet weights and designs in both lead and jacketed. There are numerous loads that even use the same powder charge(or within .1/.2 grain) and 9mm always has at least 100 if not 200 FPS advantage. If you can't get 9mm to preform better than 38 Special that is a big problem.

Maybe a more specific question or an actual example of what you are trying to accomplish would help. Posting gibberish and making wild assumptions is impossible to decipher.

 

[TomkinsSP]

For the purposes of this discussion I own three smith and wesson J-frame revolvers, a M40 (.38spl) with a 1 13/16" barrel, a M640 (.357mag) and a M940 (9x19) with 2 1/8"barrels. I have slugged all three barrels and they are the same within my micrometers ability to measure. I have filled full lenth sized (but not decapped) fired starline brass with isopropyl alcohol using a syringe. 9x19 holds equivilent of 13.3 grains of water at 77'F, .38 holds 24.1, .357 holds 27.0. I like 100% metplat lead wadcutters, my current favorite is a 150 grain dropped (by Matt of Matt's Bullets in Arkansas) from a H&G 244 mold. I loaded one each into 9x19, .38 and .357 brass (full length sized and decapped, without primer or propellant) and roll crimped each with a Lee die. I then measured the avalible space under the seated bullets, not surprisingly the bullets occupied the same amount of space in each case, leaving space equivelent to 6.3, 17.0 and 20.0 grains of water. (after the alcohol evaporates I fill the primer pocket with caulk and have snap caps). So under this bullet there is 2 and 69/100 times as much space for the propellant to complete its conversion from solid to gas (if this occurs within the case as I desire). The cylinders are the same length, gap is the same, the nine has a slight advantage 5/16" in the cylinder and 5/16" in the longer barrel (if some of the burn occurs after the bullet is released from the case). I specifically do not want a fireball created by unburnt powder leaving the barrel.

 

[Rule3]

For the purposes of this discussion I own three smith and wesson J-frame revolvers, a M40 (.38spl) with a 1 13/16" barrel, a M640 (.357mag) and a M940 (9x19) with 2 1/8"barrels. I have slugged all three barrels and they are the same within my micrometers ability to measure. I have filled full lenth sized (but not decapped) fired starline brass with isopropyl alcohol using a syringe. 9x19 holds equivilent of 13.3 grains of water at 77'F, .38 holds 24.1, .357 holds 27.0. I like 100% metplat lead wadcutters, my current favorite is a 150 grain dropped (by Matt of Matt's Bullets in Arkansas) from a H&G 244 mold. I loaded one each into 9x19, .38 and .357 brass (full length sized and decapped, without primer or propellant) and roll crimped each with a Lee die. I then measured the avalible space under the seated bullets, not surprisingly the bullets occupied the same amount of space in each case, leaving space equivelent to 6.3, 17.0 and 20.0 grains of water. (after the alcohol evaporates I fill the primer pocket with caulk and have snap caps). So under this bullet there is 2 and 69/100 times as much space for the propellant to complete its conversion from solid to gas (if this occurs within the case as I desire). The cylinders are the same length, gap is the same, the nine has a slight advantage 5/16" in the cylinder and 5/16" in the longer barrel (if some of the burn occurs after the bullet is released from the case). I specifically do not want a fireball created by unburnt powder leaving the barrel.

What the heck does the above have to do with the Price of Tea in China or anywhere else?

What are you trying to establish? Perhaps follow this guide.

 

[reddog81]

Just use powder with a flash suppressant, something like BE 86. Easy answer to a simple question.

I'm not sure what case capacity or rimmed vs rimless cartridges has to do with that question.

Are you seating the 150 grain bullet flush in the 9mm case?