Most factory original nipples are sized for #10 caps. The RWS caps are effectively #11. If you are changing the nipples to upgrade be sure that they match the cap size. I have a revolver that with the nipples that came with it, will not fire standard #10 or #11 caps. It will fire #11 magnum caps, but the #11 caps are a loose fit and often fall off and jam the works. The strength of the magnum caps blows the caps apart even if they are pinched to fit. I spent a fair amount of research time because I needed a longer cone on the nipple to have the cap and the hammer meet to ignite the priming compound. So when looking for new nipples, make sure the overall length of the replacement nipples matches the length of the nipples that work on your revolver. I have a set of new nipples to try.
More powerful caps are certainly safe to use, but watch out for cap jams.