I've never had the pleasure to shoot or even handle a Ruger Deerfield, but being that it is a semi-automatic rifle, I would
ASSUME that it takes a certain level of "OOMPH!" from your handloads to ensure that the rifle properly runs and feeds, yes? As such, you may be really pushing the limits of what a plated bullet can do (or should be asked to do?) given not only the typical velocities of .44 Magnum, but here again running .44 Magnum with increased velocity due to a much longer rifle barrel.
Berry's tends to suggest not exceeding 1,200 FPS with their plated bullets unless you purchase their TP (thick-plate) slugs, of which they do not currently produce in a .429" diameter. Xtreme makes a terrific plated slug and they recommend you don't exceed 1,500 FPS with their slugs, and only use a light taper crimp. .44 Magnum by it's very nature benefits from (and in many cases,
requires) a solid roll crimp.
In my opinion, plated slugs aren't the best answer in your situation with a Ruger Deerfield carbine. With that said, the most cost-effective method I have yet found for true jacketed and high quality .429" slugs for use in the .44 Magnum has been the 250-ct "bulk" pack of Nosler 240 grain .429" JHP slugs. I haven't shopped for them in a while, but have in the past considered it a successful buy to find them under $60 for 250 slugs. Compared to single 100-count boxes of jacketed .429" bullets, these are a fine deal for a
very good bullet.
And no compromises.