Ahh, yes. Now we can get to the meat and potatoes.
I don't have a lot of experience with plated bullets, but I do have a little bit. I was advised to treat them just the same as a hard cast bullet, and use the same data, as the plating is so thin as to be of no effect on the interior ballistics. That's what I have done with the few that I've loaded, and that advice has worked well.
That said, H110/296 probably is not the best powder for plated bullets. Not to say that it can't be made to work, but there are myriads of better suited powders available for that type of bullet. H110/296 is a "full throttle" powder... start loads are only 3% less than max loads, and it needs a heavy crimp to help get the party started... all things that are not suited to the nature of plated bullets.
The problem that you are having is that there is not enough resistance to the initial movement of the bullet for the pressure to build to the point needed for proper progressive burning of the powder. So, because of this, you get bloopers like you are seeing.
I would recommend, were it me, to try some Alliant Unique, Lyman 50th shows you can get about 1400fps at the top, about 1100 at the start with a 120gr cast bullet, which is close enough to your 125 that you could start with this data and work up. 296 is not even one of the listed powders for any cast bullets at that weight... it is not listed until the 150gr and higher weights.
If you like the slow burning powders, you could use Alliant 2400, which would give you similar performance to the H110/296 you are using now.
There's lots of powders that you could use, but unfortunately H110/296 isn't really suited for what you're trying to do I'm afraid.