Slide guitar..............?

-i have an acoustic with phosphor bronze strings. the actions low. i recently got a dunlop brass slide but its sounding buzzy when i put it on the strings and when i take it off. should i get a glass slide? i got a brass one because that's what lots od people recommended for an acoustic. maybe i need more practicing or maybe i need a new slide. and if i did go for a glass slide what type should i get?