Is it safe to use a Presta valve tube in a Schraeder rim WITHOUT the adaptor? I'm doing that right now, Presta in the rear tire and Schraeder in the front tire . I though it was probably ok since the entire Presta valve stem is metal. I'm converting to Presta so that my spare tubes will work with the other bikes I ride with.
I've done this off and on over the years for many miles with no problems. You are using the little nut to hold in place right? If you want more peace of mind there are both plastic and metal hollow shims designed to fill that space, but you should be fine.