Steel.... I don't think 5/8 is gonna be deep enough for the glute. I'd suggest a one or 1 1/2 inch for the glute. You can still keep the 25 guage... that's what size I use to inject anything.
Hey BBV
Is the soreness anything close to the PGF2a shots. My shot sites are pretty sore but if I take them in the evening then they are gone by morning.