For that riff (I'm sure you all know the song) I do two things that I'm not sure are using bad technique or not;

1) I usually alternate pick everything, but not this. It feels too awkward. I use D D U D D U D D U etc. Is that bad for this riff?

2) Also since all the palm mutes are on the E I just keep it palm muted the whole time. I can play with taking my palm off, also, but it's just more movement that I don't think is necessary. What do you think?
1. I would be alternate picking that. Though it might actually be played all downstrokes.

2. Doesn't matter.
1. It's up to you. If it feels awkward, it might just be a rhythm you need to work on, but do whatever works.

2. Why would that be a problem? Of course you can keep it muted the whole time. As long as you aren't muting the A string, there's nothing wrong with that.
I used to down pick all of that. Now I would alternate pick it.. But down picking all of it might help if you're considering moving on to more technical stuff with economy picking and stuff.
it depends how far you are willing to go to play it "properly". Hetfield plays it all down strokes and mutes the E string, so as long as you're not muting A then that's ok, but to go for the full effect then down strokes all the way man, it also sounds more aggressive that way.

Make me laugh people... go ahead, make me laugh...
i would play it all downs, at least for the palm mutes, theyve got more bite. i usually dont alternate pick palm mutes unless there its too fast and there is no other way to do it. btw on the recording its all downs, not just master of puppets but almost any mettallica song with palm mute riffs. this is true for most thrash metal bands of the 80s
I'd alternate pick the whole thing, I'd also release the mute whenever it's not needed. Otherwise you could be using it as an anchor and may face problems at higher speeds.
Speed is a by-product of shut the fuck up.
Quote by Survivalism
In the end, all that really matters is how it sounds when you play it.


And as long you don't feel any pain on your picking hand, then your technique is fine.
Besides being a guitar player, I'm a big fan of the guitar. I love that damn instrument. Steve Vai

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Quote by El Cumanés

And as long you don't feel any pain on your picking hand, then your technique is fine.

Not true, I used to play with awful technique and I never experienced any pain. I did, however, hit a lot of barriers when it came to speeding up. Now that I've revamped my technique I'm much faster than I used to be, things sound better, it's easier and it feels better too (although like I said, the other was never painful).
Speed is a by-product of shut the fuck up.
Hetfield downpicks it.

It also feels better to downpick it I always noticed, like you feel all tough n' shit.
I would alternate pick, judging by your current skill level. I would only downpick that after I'd worked with it with a metronome for a bit. Downpicking at that speed usually builds shittons of tension on your arm.