Reloading Press: .357 Magnum (9x33mmR)

The Reloading Press is an at-least-weekly feature here on Gaming Ballistic for 2016. Each week it looks at some interesting real-world cartridges and presents them with hopefully-useful information in GURPS Format. Except when it’s interrupted by a massive writing project, then it’s not every week.

But by special request, here’s the first of several revolver cartridges, which have been sadly neglected on The Reloading Press to date.

.357 Magnum (9x33mmR)



The .357 Magnum was developed in 1934, and the first weapon to chamber it was released in 1935. It was developed in response to the .38 Super (which incidentally was found to penetrate the bulletproof  – bullet-resistant, thanks – vests of the day. That required a faster bullet, as those vests were proof against anything slower than 1,000 fps).

Well, the .357 would eventually far, far eclipse this. More on that in a moment. 

Regardless, this is a very high energy cartridge, and the pressure is about double that of the .38 Special that was the foundation of the design. This led to the case being lengthened by about 3mm to prevent being able to close the cylinder on .38 Special revolvers accidentally loaded with .357M cartridges, which can be counted on to have very poor outcomes to the weapon and the shooter.

The .357 and .38 cartridges both fire 9.07mm bullets (actually .355 to .357″); the .38″ refers to a naming convention used for the outside diameter of the cartridge case.

In any case, this for a long while was the standard reference cartridge by which – rightly or wrongly – all other self-defense and law enforcement cartridges were judged. You can see this in many period writings, and even the more-recent .357 SIG hearkens back to the power (and given the loading below, that is both literal and advertising power) of the .357M harnessed in a conveniently sized automatic platform.

But there’s no question: the .357 is a powerhouse, and revolvers chambered in it with barrel lengths from 4″ to 8″ are bad news if you’re on the wrong end of them. The power is such that they made somewhat-attractive snub-nosed backup guns as well, though having fired one myself, for this purpose a small-frame 9mm is probably a better choice. More on that later.
Ballistic’s Calculator Inputs

Basic inputs for the calculator are as follows, selecting 101.6mm (4″) for the (test) barrel length.

INPUT
125gr .357M
Chamber
Pressure
35000 psi
Barrel
bore
9.1 mm
Case
Length
33 mm
Chamber
Bore
9.1 mm
Barrel
length
101.6 mm
Bullet
Mass
125 grains
Aspect
Ratio
1.7 L/Bore
Burn
length
40 mm
Projectile
Caliber
9.1 mm
Total
Accelerated Mass
125 grains
Expansion
Ratio
1.95 expansion
Projectile
Load
1



Output Stats


The .357M has a lot of chamberings available for it. Everything from about 7 to 12 grams (110 to 158 gr), with the most common seeming to be 125gr and 158gr. Both are available in a wide variety of energy ranges, and some of those energies are shockingly high. The highest energy projectile found develops 1,700fps out of a 4″ barrel. The military 9mm is 124gr and develops 1,250fps out of a 5″ barrel. So yeah, it’s a monster. 

As per usual, I selected the biggest and baddest load to do GURPS stats of, because players will usually gravitate towards this.

Notes

  • The velocity is at the muzzle. The velocity with a 4″ (101.6mm) test barrel is tuned to match real-world data at 1700fps with a 124gr JHP bullet. This might not be the very highest energy .357 available, but it’s likely close.
  • Velocity out of shorter than a 2″ barrel falls off dramatically – you can lose 1d per 2mm of barrel in this range. 
  • The bulk of a .357 cylinder would suggest perhaps going with the 9mm or similar loads actually tuned to deliver performance out of a shorter barrel.
  • I very strongly suspect that the “tipping point” where the propellant charge no longer accelerates the bullet falls rather lower than the 6d damage shown here. This site, “Ballistics by the inch,” shows a 125gr .357M getting the best velocity out of a 16″ barrel, falling from 2000fps down to 1740fps by adding 2″ of barrel. So cutting off damage increases past 16″ of barrel is probably legit.
The very, very good results from 3″ to 16″ barrels make the .357M a versatile cartridge, especially in situations where carrying more than one type is impractical for whatever reason. 

The very, very good results are also a direct result of taking the highest energy I could find. A more reasonable 125gr projectile that is tuned to 1450fps from a 4″ barrel, or a 158gr hunting load at about 1250fps (9mm velocity with a heavier bullet) will both deliver about 3d damage from a 4″ barrel, a 15% reduction. The lower powder burn length required in the model will also tend to tap out the velocity at lower barrel lengths as well.

The JHP with modern design is quite impressive, expanding in this case to 1.95x its starting diameter, or about  17mm – enough to legitimately earn a pi++ modifier. Damage falls to 2d+1 in the model, but 2d+1 pi++ is nothing to sneeze at, being both more penetrating and equally expanding as a .45ACP.

GURPS rules don’t allow that, but the same bullet would do 3d (0.5) pi+. 

So my model would predict 8 points of penetration, and 16 points of injury. GURPS RAW would be 5.25 points of penetration, 15.75 points of injury for the JHP bullets, compared to a flat 10.5 points of penetration and injury for FMJ rounds.

Platforms


The platforms here can be summarized quickly. Sub-nosed revolvers, moderate-barrel revolvers, big-honkin’ barrel revolvers, one or two insane semi-automatic pistols, and lever action carbines.

Starting with the rifle, you can expect a 16″ barrel and 8-round or 10-round capacity, and probably Acc 4 from this. It’s handy and will allow you to get the most possible velocity out of the very effective .357M.

Next comes the semi-auto, which is basically either a 1911-style frame (Coonan sells one), or the venerable and oft-discussed Desert Eagle. We’ve seen the DE before, so I’ll find a picture of the Coonan.

Lastly, we have revolvers in various frame sizes and barrel lengths. The manufacturers (S&W itself in the image shown) have done a nice job of giving options from “beefy” to “svelte.”

8 thoughts on “Reloading Press: .357 Magnum (9x33mmR)

  1. That's quite the hot round – 3d is the Model 27 given in High Tech; even a 4" barrel shooting this stuff out does it by +2 already!

    Do you just use your ballistics spreadsheet straight for this, or do you have a customized one? There's a few rounds I've been wanting to do in the same style as this.

    I've also been wondering how you get your D&D numbers; it's given as a flat number here, but typically d20 used dice for guns? Is that no longer the case?

    1. ​That just means I'm picking a certain cartridge and barrel combination to match.

      What I do is put in the stats. I use the a pressure I can find that represents the usual average maximum pressure for a round (this can be tricky to find). The caliber and case length are usually easy. I tend to use the diameter of the cartridge at the shoulder for chamber diameter, if the cartridge has one. Barrel length is from the "test barrel" column. Once I put in all of the stuff I can read, I use Goal Seek (there it is again) to adjust the Burn Distance (or Burn Length?) to the point where the velocity at the muzzle matches the reported value in Wiki or whatever I'm using for my source.

      That's "tuning."

  2. Out of interest, what load are you assuming for this?

    And how would it change if we assumed popular TL7/early TL8 police loads instead? Like the 145-grain Winchester Silvertip that was often used by agents of the FBI that wanted a hotter load than the +P 158-grain SWCHP .38 Special load issued to agents.

    For a lot of games, the PCs are armed with .357 Magnum revolvers because that’s what FBI men or detectives carried in the real world. It’s helpful to know the stats of typical issue or approved private purchase ammo from their service weapons (which are usually 2.5-inch to 4-inch revolvers).

    1. That information is in the post: it’s 124gr at 1700fps. I always try and choose the highest energy load available because that’s what PCs tend to gravitate towards.

      And you really should say “for a lot of MY games” there, since most games I have played in don’t give a crap about what load they carry – they just focus on the weapon.

      Got to get ready for work, but if you can find a bullet weight and velocity out of a known barrel length for the load you want, I can quickly generate a data table for that load.

      1. Sorry for being unclear. I do realise you specified projectile weight and velocity in the post.

        I meant to ask which real world load (manufacturer and brand name) you were modelling with those stats, as knowing the type of ammo allows me look up when it became commercially available and if there are any legal constraints on characters with LE-type jobs carrying it in their duty weapons (handloads and exotic custom ammo are often prohibited for official carry; with some agencies only allowing specific ammunition or a list of accepted types).

        I’m aware that caring about the specific loads is very much a minority view. Some previous Reloading Press articles have made distintions and even mentioned specific loads PCs might use, e.g. the 9x19mm, 5.56mm NATO and other articles on common service ammo.

        So it would be neat to have the same for the .357 Magnum, as any realistic Cops/Mysteries game set anywhere from 1940s until the 90s (TL7 to early TL8) that features guns at all will feature some revolvers in that chambering.

        The Winchester Silvertip 145-grain JHP is rated 1,290 fps from the manufacturer, probably in a 4-6″ test barrel. It clocks at around 1,175 fps from a 3″ barrel.

        I’d also love to see analysis and stats in different barrel lengths for the .38 Special loads most FBI agents and cops actually carried in their service guns as well. If you are ever interested in doing a Reloading Press on the humble .38 Spl, it would be easy enough to find velocities for the +P 158-grain SWCHP and the later Hydra-Shok +P+ 147-grain JHP.

      2. There seems to be an Internet consensus that the 2010s vintage Winchester Silvertip 145-grains that are factory rated at 1,290 fps from a 4″ vented barrel are vimpy new-fangled things, probably reduced in power by Dimmikrats, lawyers, bureaucrats or beancounters, if not all of these in conspiracy with Satan, lizard-people and dinosaur-riding Nazis from the Hollow Earth.

        Chronoing of Winchester Silvertip 145-grain ammunition purchased before the turn of the century pretty consistently seems to yield 1,370+ fps from full-size carry revolvers and at least 1,240 fps even from a 2.5″ barrel.

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