Look at the pith on one of the shoots. Red osier has a white pith, while silky dogwood has a tan-to-salmon colored pith. I know you probably can't tell at this time of the year, but red osier has whitish berries while silky dogwood has dark blue berries. They both like to grow in moist areas like the edges of swamps & streams. I've made LOTS of arrows with silky dogwood, and it does make good arrows, although I find that they require more frequent straightening than, say, Southern arrowood viburnum (my personal favorite). Grooving the shafts before heat straightening them may help, and I've been told that burnishing the heck out of them after straightening helps as well. I'm even more picky about picking shoots for shafts with this species, harvesting only the straightest shoots with very limited branches. I usually cut shafts that are about 1/2" or so at the thick end tapering to about 3/8" or so at the top end (I plane them down to a uniform diameter after they've seasoned, and I'd rather have too large a shaft than one that's too small to use). Hope this helps.
Will