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Ballistician's Notebook: The .357 Mag

Ballistician's Notebook: The .357 Mag


The .357 Magnum caused quite a stir when introduced in 1935, but it took several decades for it to gain wide acceptance. A 158-grain lead semiwadcutter bullet was the only load available from the major ammo makers until the 1960s and was the culprit of fouling many bores with a heavy coat of lead. Once better ammo and components were available, and gunmakers introduced less expensive revolvers, the .357 Mag. was on its way to becoming one of the great handgun cartridges.

It's All About Pressure

The .357 Mag. case is 0.135 inch longer than the .38 Special, primarily to prevent its being chambered in a weaker .38 Spl. revolver. The extra case length adds little propellant capacity; it was the choice of propellants and greatly increased pressure that let the .357 Mag. double the velocity of many .38 Spl. loads in the 1930s.

The .38 Spl. started as a blackpowder cartridge, so the case is rather spacious for smokeless propellants. Early experimenters, including Elmer Keith, Phil Sharpe, and others, used the extra capacity to load the .38 Spl. with fast-burning rifle propellants like Hercules 2400 and DuPont SR-80. Their test platforms were heavy-frame .38s whose cylinder diameters were the same as a .44 Special cylinder. These included the S&W 38/44 and the Colt New Service and Shooting Master. Through trial and, yes, error, these early researchers found they could achieve a massive velocity increase over the fastest .38 Spl. factory loads.

The modern maximum average pressure (MAP) of the .357 Mag. is 35,000 psi, 75 percent higher than the .38 Spl. +P. This extra pressure combined with propellants that release energy slowly made the velocity gains possible.

Match Propellants To Bullets

Early in my reloading, I found I had to be smart about propellant choice when loading the .357 Mag. to top velocities. As an indigent grad student with a limited propellant selection, I tried getting top velocities from 160-grain cast bullets using Unique. Nothing broke, but the recoil was sharp enough to open the loading gate on my three-screw Ruger Blackhawk every time I pulled the trigger. Call it a "clue."

The "full-weight" bullets for the .357 Mag. were, at that time, the 158-grain versions. For hunting, these heavy bullets offer deep penetration and retained weight. Hodgdon H110 and Winchester 296 were hard to beat back then and are still my choice for bullets of 158 grains or more. However, 2400 and VihtaVuori N110 may produce less velocity loss across the cylinder gap in some revolvers.

As lighter bullet options appeared in the late 1960s, the effects of burning rate became evident. The 110-grain bullets did not like H110 and W296; the light bullets didn't offer enough resistance during the pressure rise, and pressure and velocity variations were high. Slightly faster powders like 2400 bettered the slow spherical propellants but still posted inconsistent velocities. I loaded Unique under 110-grain bullets largely because I found that a major factory producing a very nice 110-grain factory load was loading it. Today, we have many new propellants that would fill the bill: Alliant Power Pistol, Accurate No. 7, Ramshot True Blue, Hodgdon Longshot, and others sit firmly in the "sweet spot" for 110-grain revolver loads.

For bullets between 125 and 145 grains, I like to go a little slower. Although H110 and W296 are certainly appropriate at the upper end of this weight range, I've been pleased with slightly faster propellants like 2400, VV N110, AA No. 9, and Ramshot Enforcer.

The Velocity Shift

Remember that there is a significant difference between the velocity from a .357 Mag. pressure test barrel (10-inch unvented) and most revolvers (see the accompanying chart). Slow-burning propellants combined with light bullets often produce the greatest shift. The propellant preferences above take this into consideration. This becomes especially important if you have to load to a particular velocity or energy level.

We tested a number of .357 Mag. revolvers at Speer, all with 6-inch barrels. The velocity variation among different revolvers of the same make and model was rather high. Remember, the velocity shown in reloading publications will seldom be what your revolver produces. It's the basic nature of revolvers. An inexpensive chronograph is the best friend a .357 Mag. reloader can have.

A wider cannelure (right) helps establish a more effective crimp when loading Magnum revolver cartridges.

Don't Forget The Crimp

I think that many problems I encountered in my early days of reloading Magnum cartridges could be traced to inconsistent crimps. Then, most loading dies featured an abrupt crimp shoulder made to match the deep, V-shaped crimping cannelures of cast bullets. Jacketed bullets tended to have narrow, shallow U-shaped crimping cannelures. Applying too much crimp force would easily crumble the case mouth. Fortunately, newer dies have a crimp shoulder balanced for both bullet styles, and jacketed bullets are now available with wider cannelures, up to 0.060 inch compared to the older ones at 0.030 to 0.040 inch. The wider crimp cannelure lets you lay a bit of the case wall into the groove to produce a neck-down crimp with greater holding power than the conventional roll crimp.

A case trimmer is another tool that helps with uniform crimping. I've seldom opened a box of new cases that were all the same length. I learned to batch-trim cases to uniform length if I want truly uniform crimping, regardless of the bullet I load.

Cases For Accuracy

I once thought that accuracy would suffer if I shot .38 Spls in a Magnum cylinder. Then I learned from a friend who was building target revolvers from Model 19 S&Ws that he consistently made factory .38 wadcutters shoot tiny groups at 50 yards. I gave up on the issue when I shot one of my iron-sight best groups--just over 3 inches at 110 yards--with a 5-inch S&W Model 27 loaded with hot .38 Spl. handloads and the Keith 171-grain cast bullet. That's one less thing for me to worry about.

Handgun hunting spurred development of jacketed bullets that were heavier than those formerly considered to be "standard" weight. In .357 Mag., we saw weights from 165 up to 200, but the expanding versions are usually no heavier than 180 grains. With the velocity drop in revolvers, you need to establish the velocity you want and use a chronograph to be sure you meet the goal. Heavy bullets rely more on penetration than expansion to accomplish their task, so velocity becomes more of a f

actor in flattening the trajectory than making the bullet mushroom.

Whether you handload or shoot factory ammo, knowing the velocities your revolver produces is important to a .357 Mag. shooter.

.357 Velocity Change

Powder (type/grs.)Velocity (fps) 6-in Revolver BarrelVelocity (fps) 10-in Pressure BarrelVelocity Change(fps)
Speer 135-Grain Gold Dot
H110 / 18.513871819432
W296 / 18.513771835458
2400 / 16.013771729352
AA No. 9 / 15.513451707362
Power Pistol/ 9.612911571280
VV 3N37 / 8.711851432247
Unique / 7.811851395210
All powder charges are maximum.
Notes:The velocity shift between revolvers and the .357 Mag. pressure barrel tends to be greater with the slower- burning propellants.

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