They do have a few benefits compared to lead.
For instance, they have no barrel leading, they keep your seater die cleaner (Don't have to take it apart every few hundred rounds to clean all the lead rings out of it.)
I have never seen one shave during seating, the lead underneath is too soft and would just move out of the way. You can easily dent the copper plating with your thumbnail.
I use medium burn rate powders, a light taper crimp, and starting load data for jacketed rounds.
Convention thinking applied to their use would dictate fast burning powders may cause leading and slow burning powders would either not seal well enough against the back of the bullet, or wouldn't group well because of the heavy crimp necessary for consistant ignition.
Also, they are sized differently than lead or jacketed.
Jacketed bullets run fairly nominal dimensions, and have good dimensional control, as the lead is swaged INTO the jacket. I would assume it's easier to maintain dimensional stability with copper than it is lead. 9mm nominal bullet size would be .355"
Then there's swaged lead which is dead soft, and must be used with target loads, as the lead will vaporize easily, and deposit itself on your barrel like water condenses on a cold cement wall. Swaged lead starts out 1 or 2 thousanths over nominal dimensions, and swages itself to the right size. Dimensional control isn't important, as long as the bullets are indeed, larger, not smaller than the bore diameter. Undersize swaged bullets will lead barrels up in VERY short order.
Cast lead bullets vary wildly in quality, size, hardness, uniformity, and dimensional control. If you buy cast bullets, I wouldn't recommend buying them in large quantities from an unknown source, as the source determines the quality.
Good cast bullets can be tweaked to the gun they are to be loaded in, and to the velocity they are to be loaded at, by a good caster. Casting at home makes sense, as the operator can make good projectiles very inexpensively with a little attention to detail.
If you buy cast lead, they are mostly .001 over nominal dimensions. Sometimes more. So 9mm bullets would be at least .356" with the occasional one .357"
Plated bullets, for the most part, start out as swaged lead cores, and get plated in an arsenic bath with copper ingots up to the desired size. It's a nasty operation.
Then they get 'struck" into their desired profile.
Hollow points are struck again, typically.
Again, they vary wildly in quality by the maker.
Hardness is no longer a factor. Dimensional control is pretty good, as the bullets are 'struck' like modern jacketed hollow points.
They are typically sized slightly larger than jacketed, nominal size for a 9mm bullet would be .3555 on average.
You will occasionally get a few that are undersized, as they are typically not held to the high quality standards as big name JHPs.
For practice rounds, they are better than lead* (Unless you cast it yourself.), and cheaper than jacketed.
Brass didn't look the greatest either. After that I toned down my load and it worked much better. But again the accuracy wasn't really good.
