If you struggle to get this achievement in the normal way, here's a tricky one. How can one never miss a beat? You guessed it right, if the one would never shoot.
Two weapons in the game have an ultimate that kills enemies without player's attention: Hounds that create a shooting clone, and Hellcrows that create a damaging Crowstorm. There's also "Ultimate Sovereignty: III" sigil, which charges your ultimate automatically, 1% per beat. That allows you to potentially clear the whole level without shooting once. You don't even have to use your ultimate on beat, the game would count ultimate kills as perfect ones in any case.
Enter the first Hell (Voke) on Lamb difficulty. I haven't tested if beating the level without literally shooting once would suffice, so you'd better kill the first enemy. Ignore the rest and head on to the first arena. Keep in mind to never use dash, because the achievement requires you to dash on beat, too, and there's no point in taking extra risks. Running and jumping is okay.
While at arena, keep on running in circles with Hellcrows. Once your ultimate is ready, use it and start running in the opposite direction. After the third arena wait for your Hounds ultimate to be ready and head on to the boss. Use the same tactics during the bossfight, just use Hounds instead of Hellcrows. Once you'll lower boss's HP to 50%, it would summon some enemies, which would require you to switch back to Hellcrows for a bit. After that no additional enemies would be summoned, so you can stop running and wait calmly behind the pillar, which would block all the boss's fireballs, while recharching you ult.
It can take up to 30 minutes to do the achievement that way, and, truth be told, that's extremely boring, but it's also fairly easy.