I just got into it myself, and I started off using an old set of RCBS dies without the aforementioned replacement seater plug. I had no problems with heavier bullets, but I personally found when I was using smaller grain bullets such as 110 grain spitzers or 125 TNT's, I lost up to three cases in every fifty.
You said you needed to buy dies, I came across a brand new set of Hornady new dimension dies with a floating seater for $20 and change. For the price I'm very content, I don't know if anybody's had a bad experience with Hornadys.
For the RCBS, I'm going to order the replacement part as well so I just looked at their website: you best bet is to call RCBS Customer Service at 1-800-533-5000. their website was not particularly helpful for this topic
I've been having a lot of fun with mine, I'm sure you will to.
Rex