I can't answer your question directly, 16"50calNR, but I can say that if I had, and will have a turret/progressive soon (finally closing on the house with my garage/shop), I will have an RCBS dispenser or Hornady dispenser, and not the disks from Lee.
I also have debated getting a RCBS Chargemaster or Hornady auto measure, but I can use a Lee dipper into my Lyman 500, and trickle to the exact weight in less time than it takes those machines to weigh out. Although I did see a yellow machine on youtube spit out some serious weight really fast. Close to 60 grains in like 8 seconds or something crazy, but I don't need to load that fast. LOL
I have used, and still use the Lee dispenser for my TB .44 mag loads. I have to take the handle, raise it, and bump it twice, and then drop the powder, and I will get good results.
I doubt your 505 is off. Get some check weights to verify. I would be the Lee is either new, and just static prone right now, or the disks are just off.