Quote by TTeddybear

I do that 3x a day 6x on holidays. Still hasn't sped up my downstroke palm muting.
It's accomplished by improving your technique: smaller, more relaxed movements than you're making right now.

You can't make yourself faster, you can only make yourself better which may result in you becoming faster.
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

Quote by Master Foo
“A man who mistakes secrets for knowledge is like a man who, seeking light, hugs a candle so closely that he smothers it and burns his hand.”

Muscle indurance is a factor too. That is assuming you can down stroke right but can't make it last because your forearm starts burning. I mean, if you really have to play FAST you might as well alternate with up and down strokes.
Alright, thanks for the tips. I listen to bands like Fenix Tx where he has those really fast chugging palm mutes, but playing around with down/ups I can deff tell he's doing only down strokes. So I was just trying to figure out a good way to pick up my down stroke speed.
Quote by Dalymiddleboro
Is this just simply accomplished by using a metronome and gradually increasing it's speed?

This is only one way. A good way though!

Another way is to play something at faster speeds than what you can play right now even though it sounds sloppy...it it just to condition your mind to make you feel how faster speeds feel.

Also you can do little bursts which you need to do accurately since you are maybe only doing 4 - 16 notes while doing these.
Learn some Anthrax, down stroke rapage at it's finest. Indians, Caught in a mosh, Among the living etc. etc. etc. etc. .................................