Virtual wildcating: carpenoctem calibers

NOTE: This post is long. And about very pecular topic... so for the most people this text probably will not be interesting.

For some lighter blogging (after all the ruminations about politics, human rights, values etc) let's do some virtual wildcating*.

Smallest of the (commonly used) centerfire pistol calibers: 6,35mm Browning and 7,65mm Browning (as they are originally known, or .25ACP and .32ACP as they are known in USA) are usually denigrated as not-even-marginal and totally unsuitable for any real self-defence use (although any gun might work as psychological threat).
But... guns of these calibers are still used for self defence around the world. And that should come as no surprise. First and foremost, there are a lot of them in circulation (because there were lots and lots of them made by lots and lots of firms throughout the XX century). Plus, when we compare smallest and lightest of modern 9mm Short (= .380 ACP - which is considered smallest caliber barely adequate for self defence) pistols, Kel-tec P3AT, to its "older brother" in caliber 7,65mm - Kel-tec P32, we see that P32 (smaller caliber gun) is slightly smaller in size and is somewhat lighter AND holds one more round. Yes, differences are small, but they still are there. And when talking about 6,35mm... Baby Browning, production of which began in year 1931 (and which is still produced under the name PSA) is still smaller than even the Kel-tec P32 (although it is heavier than the polymer framed Kel-Tec). There is one other factor too - small guns in somewhat bigger calibers (as the already mentioned Kel-tec P3AT) have really snapy recoil - which might not be to suitable for somebody with weak hands and/or wrists.

But, as was already said, these two calibers (.25ACP and .32ACP) are not what you would call "effective". There are two "main" causes why it is so:
First - small diameter of the bullet (which obviously means small wound channel);
Second - very low muzzle energy (around ~90J for 6,35 and ~170J for 7,65) which means low penetration capability (which only slightly exceeds "required" 12 inches of ballistic gelatine).
So it is obvious, that if you want to improve effectiveness of these calibers, you have to "improve" muzzle energy and bullet diameter.

Answer to the energy question is known for a long time - increasing the chamber pressure increases the muzzle energy. That is, as long as the firearm is able to handle it, but, bearing in mind that standard operating chamber pressures for 6,35 and 7,65 are really low (acording to accurate powder 18000CUP for .25ACP and 20500psi for .32ACP (which is basically the same) - compare that to, say, 23200psi for 9mm Makarov or 35000psi for .40S&W), slightly increased pressures in good quality (steel) guns pose no problems.
Bufallo Bore is currently loading .32ACP to +P pressure levels for 300J of muzzle energy. Magsafe has .25ACP +P load which delivers 200J of muzzle energy. These loads probably should not be shot in low quality (zinc casting) guns, but they do show what is possible within the provided envelope.


It is somewhat more complicated with the second part of the equation: wound channel diameter.
Usually this problem is solved by the use of expanding bullets - bullets which drastically increase their diameter on penetration of living tissue (or ballistic gelatine, or wet newspapers :) ).
Because of low inherent energy levels expanding bullet technology is not quite applicable to these small calibers: when using expanding bullets, penetration, which already is marginal, decreases even further. According to brassfetcher:
"[When using .25ACP] It is generally advisable to utilize FMJ ammunition for both practice and carry with this caliber, as the penetration depths typical with the expanding types of ammunition usually do not exceed 8", while FMJ bullets can usually be counted on to reach FBI minimum penetration depths" and; ".32ACP cartridge typically demonstrates outstanding expansion, but penetration depths less than 12" or greater than 16" penetration and no expansion. It is very difficult to find a balance of penetration and expansion with this caliber, when fired from a short barreled pistol".
There are more problems - because of the limited muzzle energy you can not expect expansion every time. At best you could hope that 2/3 of bullets will expand (and when dealing with heavily clothed person - probably even less). Compare that to 9x19mm Parabellum where most hollowpoints do actually expand with almost 100% reliability.
So, summing it up, bullets of these small calibers expand pretty erratically, and even if they were reliable "expanders" - that would decrease penetration to unacceptable levels.

In such a case probably best bet would the use of big(ger) diameter non expanding bullet.
That sounds weird because bullet diameter IS actuall caliber and it IS (as per definition) fixed. You can't have bigger (or smaller) diameter bullets in the same caliber. But...



As the name says, this is virtual wildcating article, so I present you :) with Carpenoctem calibers: 7mm Carpenoctem and 8.5mm Carpenoctem (or .27 Carpenoctem and .34 Carpenoctem if you wish).

Ammo of these wildcat calibers could be used in guns intended for 6,35 and 7,65 cartridges and would provide reasonable (although small) increase in effectiveness. And: modified guns could even safely shoot standard 6,35 and 7,65 ammo (accordingly) although with horrible accuracy and (very big) loss of muzzle energy :). But I am getting ahead of myself...



Some time (a few years) ago stumbled upon .480 Achilles (you should probably go there and read the whole thing). In short: .480 Achilles is a caliber which uses heeled bullet in shortened .45 Colt cartridge cases to shoot .475 diameter bullets. As I said - you should probably go read the whole thing - there is explanation of what a heeled bullet is, and what sort of problems can be expected (Aaron Bittner: At first I thought the of the presence of the heel as a real handicap. Heeled bullets require outside lubrication which tends to attract dust and dirt. A heel also reduces bearing surface on the bullet for a given weight. Heeled bullets require special tooling to crimp. Nevertheless heeled bullets have been used successfully for over a century; witness the humble (and hugely successful) .22 Long Rifle.**).

After I read the article(-s) it dawned on me, that actually most useful application for this sort of cartridge would probably be in smallest calibers - because you would get increased bullet diameter (which is "at premium" in these small calibers), but keep overall size of the cartridge the same and that means also the size of the gun remains the same - because the diameter of the cartridge body does not increase, barrel chamber size will not increase, chamber wall thickness remains the same and allows the same chamber pressures etc etc etc...

Actual diameter of the bullet of the 6.35mm caliber is 6.38mm (.251''). Diameter of the case is 7.06mm (.278'') - this means that using heeled bullet this would be the diameter of the bullet. Although increase in the diameter of 0.71mm (.027'') might not sound to impressive (although it's still bigger by almost 10 percent) that's a full 20 percent increase in cross-sectional area of the bullet.
Looking at 7.65mm caliber, actual bullet diameter is 7.85mm (.309''), case (= heeled bullet) diameter 8.58mm (.338'') - increase of 9 percent in diameter and 18 percent in cross-sectional area.

Increases are not ground braking, but, we have to bear in mind, that we are dealing with very small calibers - and every little bit helps :). And, it should be mentioned, that going from 8.5mm carpenoctem to 9mm Short (.380 ACP) would give increase of less than 6 percent in diameter and only slightly more than 11 percent in cross-sectional area...

Best part of it - only needed change to the pistol is a rebored barrel (well, and there might be a need to recut the chamber in the barrel (which in this case is really simple, considering that the whole cartridge, including the bullet, is pretty much straight) and recrown the muzzle - which is usually normal part of barrel reboring). .277 and .338 are pretty common bore diameters so rebore to these calibers is not a problem. Btw., aforementioned Baby Browning has removable barrel and therefore is prime candidate for such conversion (ok, so Kel-tec P32 could be converted too... like some other handguns).

There are no real problems with headspace either - differently from most other pistol calibers, 6.35mm and 7.65mm were designed by J.M.Browning to headspace not on the case mouth, but on the semi-rim (which is of slightly bigger diameter than the case body).


Getting back to the "shorcomings" of heeled bullets... well it's XXI century and the problems with bullet lubrication which were very important in the end of XIX century can nowadays be solved without to much of a problem.
For one, most bullets today are jacketed bullets which do not pose any leading*** problems (that means they don't have to be lubricated). Even cast bullets today could be coated with dry film lubricants (an example) which are not sticky (do not gather dirt) and solve the leading problems.
Home tinkerer could copper electroplate the lead bullets or just use Lee Liquid Alox and powdered mica (as was originally done with .480 Achilles).

Another thing which does pose some concerns is bullet bearing (surface) length of the heeled bullet.
Some playing with Mountain Molds online bullet mold design software let me create a 7mm carpenoctem 61gr naked weight .415 long bullet with .130 long heel which should have ~.240 of the bearing length. Would that be enough? Well, we are talking here about low powered pistol caliber - so probably yes (then maybe not - that would be known only after some real life testing)...
Because 6,35mm has excess case capacity****, heel could be lengthened at least by another .04 in and maybe more (with commensurate increase in bullet weight), but to long a heel would be undesirable from the bullet stability point - long heel could easily kink to one side when traveling down the bore which would lead to deterioration of accuracy (not that accuracy for such calibers would be main priority).


So, summa sumarum:
Slightly bigger and slightly heavier bullet at the same (or slightly increased) velocity (in standard unmodified cartridge cases only loaded to slightly higher pressures), which provides slight (slightly less than 30% when judging by TKO factor) increase in "stopping power"*****. And it would require only slight modifications to the pistol - reboring the barrel.

Is it worth it?
Well, actually... sanely thinking about it - not at all :) - 7mm and 8.5mm carpenoctem are only slightly less un-effective than their parent cartridges 6,35mm and 7,65mm Browning - and for self defence even ubiquitous 9mm Short would still be far more recommended.
But wildcatters are like car hot-rodders - they are always trying to improve things... just because they can... :DDD




And the last thing: about the name of the caliber.

Carpe noctem from latin means "pluck the night" (= seize the night).
For one this name is a respectfull nod to the Horace's "carpe diem".
For two - this is another respectfull nod. This time to Georg Luger who designed the pistol (and corresponding cartridge) named Parabellum, which comes form latin adage "Si vis pacem, para bellum" (If you wish for peace, prepare for war).
And for three... well it just points to intended use - seizing the situation on those nights when a small gun in a pocket just might be needed.


Carpe noctem...



_____________
* For those who do not know it - wildcating is process of desinging new wildcat cartridges. Why this (my) exercise is virtual? Well, because actual wildcating in Europe (unlike the USA) it is "not quite" possible ... purely theoretically you could do that, but you would have to jump through a such a lot of financial and bureaucratical hurdles, that it is not worth it :/
** 22lr - most common caliber in the world.
*** (Undesirable) coating of the barrel interior with molten lead, which occurs when shooting cast bullets and which leads to all sorts of problems with the gun.
**** Which means, that normally cartridge case under the seated bullet is never full of gunpowder, see here.
***** And yes, I know there is no such thing as "stopping power", Taylor KO factor is "science fiction" and there is no replacement for (hit) placement :). But here we are trying to compare calibers (one of which does not exist) - not shooters, - and for basic (preliminary) comparison of effectiveness TKOF is usefull. Here is a Table of "empirically derived" (i.e. speculative :) ) "typical" data (bullet diameter in inches; weight in grains; velocity in feets per second; energy in foot-pounds.):