I have the dispenser/scale combo and it's great, never had any real problems with it. If it over or under charges a throw, it says so. I always zero it out each time I turn it on, check it against the beams, and I also do random checks with a beam scale as I load. Always dead on. My loading process using this thing has reduced my velocity spread to a consistent average, and I haven't had a squib, over or under charged load since I've started using it. Well, not one that's made it past me. Some powders just throw poorly, nothing you can do about it (except maybe the straw mod). But you should be catching these poor throws, not loading 'em.
I'm assuming you zero that scale each time you turn it on? And check it to the beams now and again? And when your charge is ready, do you wait until it beeps and the screen displays the final number? Is there an up or down indicator? That indicates your charge is over or under. When it dumps the charge, the weight will look fine WHEN IT HITS THAT WEIGHT and it'll stop dispensing --and you can be tempted to just pull the pan as soon as it hits that weight. But if you wait a bit, you may find that charge is over or under when the final number is displayed. It weighs the charge as it goes in, stops, then weighs the final charge, beeps and flashes the final number. THAT is when you are supposed to take it.
If you're doing everything by the book and waiting on the final weight and that looks good, you've got only one way of finding out if the scale is faulty: check each load against a beam scale until you hit a large discrepancy like you mention. Then I'd be calling RCBS and asking about changing that scale or unit out.
The straw mod is something I plan on doing soon, it'll reduce the amount of over and under charges you get with certain powders that measure difficult. But you still have to wait for that final number.
I think there's an environmental issue to take into account, but I could be wrong and I can't remember what it is: no magnets or metals very close by, no crossing the power cable perpendicular with another, something. I know it has to be setup right on a flat and stable table top in order to be consistent.
As for other brands, I looked around a few years ago when I got this thing. It seemed like there's not much difference between the three or four major makers, and it comes down basically to the features you get, want. All the scales are the same type and the same tolerance, 1/10gr. I think I went with this one because I have RCBS stuff already and it had some of the features I wanted that the others didn't.
FWIW, US Marine marksmanship unit or team or whatever, their shop that handloads all the ammo, they use RCBS gear and this is the exact same scale/dispenser they use.
Good luck, I hope you get to the bottom of it. Sorry to hear it's giving you grief.
