whatever you wanna call it. im getting a lot better at the gallop in most trash songs -angling the guitar differently as well as the pick itself..but when it come to a pure downpicking attack i tense up and my forearm gets super burned out. ive heard both styles should be played with your wrist but the harder i try to go faster i tend to use my entire arm. what can i do to get that hypnotic sound im looking for in either style? ie. the gallop in Metllica's disposable heros.
You really must try to relax as much as possible and pick really hard. Also, the classic thrash sound is usually achieved with scooped mids, so lessen the mids on your amp helps you get the sound, too.
Yes, you should use your wrist and as Archer said you really need to focus on relaxing. That goes for anything you practice on the guitar. It is extremely important to keep this in mind, and if you tense up, stop for a second and relax.