The problem with plated bullets is they are usually a softer lead, and the plating is there to mask the symptoms of improper loading, which is leading, which is the standard everybody seems to use for whether its a good load.
Soft lead works great and very accurrate at lower pressures, and plating is a good cure for minor leading, and can allow you to drive it a little faster without leading. This cleans up a lot of very minor issues in semi-autos, which have a limited range in which they function BUT when you start pushing them at magnum velocities in revolvers, they begin causing problems you don't see as obvious barrel leading.
The pressure from ignition makes the base of your bullet expand to a tight fit. the softer the lead, the easier it expands. In a revolver, the chamber is not directly attached to the barrel, so your bullet can over expand before it goes into the forcing cone and is squeezed back down to barrel size. The more a bullet expands, the more undue wear on the forcing cone, and the more pressure build behind the bullet. On an unplated bullet, you would see excessive leading, and back off your load. Plated bullets may hide that symptom. I've seen very little reloading data that actually does pressure testing on plated and coated bullets. Freedom Arms warned extensively about the accelerated wear on the forcing cone from standard soft lead core jacketed bullets, and the importance of thick jacketed, harden core bullets in the .454 Casull when it was first released. While .357 and .44 don't carry near these pressures, the principle is the same, and coatings do not equal copper jackets when it comes to helping the bullets hold their shape.
What this means is that it is still important to know and understand the hardness of the bullet under the plating or coating, because while it reduces leading, it does not reduce bullet expansion.
Exposed lead is a natural lubricant, and once you coat it, it takes more pressure to get a bullet moving. This is why it is recommened to not drop below jacketed STARTING load data. Softer coated bullets should not be driven much faster than uncoated cold swaged bullets. This is why it is recommended to not exceed mid range jacketed data with soft lead coated bullets.
In this case the OP, is using a plated bullet with hardened lead core of BRN16-17 whcih will probably work well in the tradition magnums, but I would not try to duplicate his efforts with plated soft lead bullets.
