Interesting that the letter is also in regards to a Zinc bullet. If they mean a zinc plated bullet, one wonders why anyone would want to market something that would damage the rifling of the barrel of any pistol that fires it.

Also note that they knew of frangible ammunition but they wouldn't mention it because it involved rifle cartridges. One also wonders how the .357 magnum would penetrate automobile armor of the period when it (the armor) could stop non-armor piercing rifle rounds).

The "slow and heavy" statement doesn't seem totally bogus to me. The letter is specifically talking about avoiding shoot-through. This is the same thing that modern hollow-points accomplish, while allowing high muzzle velocity. It is also similar to criticism of the .223/5.56 round when fired at longer range, where the velocity is no longer sufficient to cause the bullet to tumble. It simply passes through, imparting little energy to the target, and making, essentially, a .22 caliber hole. From that perspective, it's plausible to argue that sufficient velocity so as to guarantee a shoot-through is not appropriate for self-defense, since the excess energy is wasted, and the bullet becomes a hazard to people and objects behind the target. This is the same reason we don't use .454 Casull or .50 S&W as a self defense round. Well, that's not the only reason, but it's one of them.

@James: I didn't interpret that section as talking about frangible ammo, but as talking about hydrostatic shock or temporary wound cavity.

This argument immediately made me think of an article in the 1951 Gun Digest in which Roy Weatherby argues for "High Velocity", and Elmer Keith argues for "Heavy Bullets".

"In Africa we learned that if we used smaller caliber high velocity bullets, the animal had to be close enough so that the bullet would not lose enough velocity to keep it from disintegrating within the animal's body... But if you can get that small caliber to disintegrate inside the animal, it will kill anything on the face of the earth." - Weatherby -

"Dangerous game is not really dangerous until it is in close proximity to the hunter, and when that is the case he doesn't need high velocity but rather a big caliber with a heavy bullet that will penetrate well and also deliver a heavy knockdown wallop." - Keith -

The argument will probably never go away...

Can't vouch for the accuracy of the claim, but it is said that the bad guys were having good luck avoiding serious harm when police bullets tried to reach them through a car door. The 38 just did not have enough juice to do the job. Allegedly, the 357 was designed so law enforcement could successfully shoot through a car door.

"the 357 was designed so law enforcement could successfully shoot through a car door"

Yes, back in the days when cars were made out of real metal.

Now days a .25 will go thru a car door.

J. Edger would have s87t a brick if he had seen a 50AE.

Joshua@ given that they emphasized it was rifle ammunition I couldn't think of anything else.