I don't think it's in the casting of the grip frames,, but the actual polishing of them AFTER casting. No uniformity because there are likely more than one person doing that job,, and as mentioned,, the Bisley shape is a bit different than the plow handle. It takes a skilled hand to polish stuff nicely AND uniformly.
And even if you purchase a RW Grip Frame,, it's oversized & you have to do the final hand fitting/polishing yourself,, OR,,, send your gun to Ronnie (or someone else,) to be done for you.
Ronnie gets $350 for a grip frame and that's w/o grips. I can't recall what he gets for a set of grips,, or what he charges for fitting & all.
The point is,, it COSTS MONEY to get top quality,, and a skilled person has to do it.
By all accounts,, the JT PPP has suffered a problem where the grip frames & grip fitment is concerned.
And I have a strong feeling that it WILL get resolved somehow. I trust Ronnie, Bobby, Jason, & yes,, Ruger to figure out how to correct this.