Nice gun! I'm also old. And, like "sherco" I've shot some nasty loads; the worst was .44 magnum. The idea is to hit what you're shooting at (and nothing else), so I tend to go with any stock loads that produce minimum recoil. Heavier projectiles with stock powder load tend to minimize recoil. Any good hollow point, expandable round is likely to do the job for SD/HD. The objective is to produce shock to stop the aggressor and keep the bullet fragments (or entire round) from hitting anything/anyone else, other than the target.

I don't have a Model 60, but do have a couple of revolvers with 4 inch barrels that handle both .38 Special and .357 Magnum. For most range practice, I shoot the .38 Special round with occasional sessions with .357 Magnum, so I know what to expect with it.

During a lot of my USAF career, the S&W .38 Special Combat Masterpiece was my duty weapon. I think it was ".38 Special", maybe just .38. That was a long time ago; I retired in 1976. The memory fades. I had a lot of trust in the gun and in the load. But, it was for close in combat use, similar to what one faces in SD/HD. For known serious situations we carried the M16 and a handgun. And, for really serious expected situations, we had a combat team and the M60.

Locks are hardly worth mentioning. Except to say, if you don't use them they're unlikely to cause a problem. A good safe is a better solution.

My best advice is to decide what you want the gun and the round to do. Select what you consider the best of both. And, practice, practice until you can handle the gun as second nature and put the rounds where you want them.