I don't think today that training with your SD ammo is as big a deal as it was in the 1970's and 1980's, more in vogue but less important, generally....
Actually I meant 629. I had a 329 PD and loved it. The only reason I sold it was that I could not get a bullet crimped tight enough to stay in place....
The heavier bullet builds up the same pressure but the lighter bullet travels faster at the same pressure. You adjust the powder charge to the bullet...
You can shoot 158's forever. Part of the problem with the lighter bullets is that they are shorter, meaning they do not seal between the forcing cone...
I do not think the GP100 is any stronger than the service/speed six just cheaper to make. My brother has the same security six he bought in the early...
I have played with many, settled on an AR pistol. I tried 5.56 and 300 AAC they are both VERY, VERY loud. I have since migrated to a AR Pistol in 40...