Loading at the range is the ONLY way to fly for load development. Once you've tried it, you won't ever want to be without the capability again. I've gone to a small Harrell's press that clamps to the side of my range box, and using regular 7/8-14 dies at the range. But the Wilson hand dies are easily the best bang for the buck in handloading. They consistantly produce very concentric ammo with a maximum portability factor.
Will the hand dies produce more concentric ammo than your regular RCBS dies? That depends on how your current dies and setup are performing. With good dies and proper setup, the answer is "no". The hand dies won't do any better. The goal is zero run-out, or as close as we can get to it, and you can get just as close with either type of die. But, it can be a bit of a challenge to get regular threaded dies and press in proper harmony to produce really straight ammo. With the hand dies, it's just drop dead easy - they have far less that can go wrong and introduce run out.
Any gains in accuracy, "of your ammo", will be directly related to the run-out just mentioned. So, as already stated, the only way you'll see any accuracy improvement is if you current setup isn't working so well. That certainly could be.
Note, I just talked about potential accuracy improvement of your ammo. The other part of the equation of course is your rifle. If it's only shooting 1 - 1.25" groups now, I'm kind of skeptical that hand dies are going to make much improvement. UNLESS, the current poor performance is due to really crooked ammo from your current dies and press. But if your current ammo is even reasonably straight, say run-out of not more than .005, I suspect your rifle isn't really accurate enough to show you much improvement by reducing the run-out to .001 or less. Some, probably, but not a lot - possibly not enough to really even detect, given the large variation in group size you are getting now. If your current setup is producing run-out of under .003, I'd say your rifle simply won't show you any fruit from improving on that.
Regardless, I'd encourage you to get the hand dies. They absolutely can't hurt, and will add to the enjoyment of your hand loading hobby - something I can tell you will appreciate.
- DAA