Shuckle(s) - Moveset

Chances are he will be attacked by Machamp. Or whatever was super effective to the previous Pokémon.
I suggest Kaefertrutz cuz Machamp resists rock, and Felswurf cuz it's 3 bar.

Struggle Bug - Gyroball is the best moveset against Tyranitar and it will take 0.58 potions against a level 30 Tyranitar. I think those are the little 20 power potions, so if the attacker will only need 60% of one small potion, and that's the best you can do...You can change the moves or leave it.

The difference between the attackers regarding Time to win will be determined by their attack stat and moves, not your Shuckle's moves. So actually, you might want to choose the moveset that is the worst against the majority of attackers to reduce their energy gain (however little effect that will have) to stay in the gym longer.

If I was the attacker, I would keep on karate chopping with Machamp as always, maybe not even use charge move depending on the next mon

Gyarados also resist steel.

Tbh, i dont think so, that Shuckle with his tiny attack will hurt any attacker...

Very simply, it doesn't matter. Dump TMs if you want to have fun. But don't expect any changes to matter.

I made the mistake of messing with a Shuckle in a gym once. Take it from me guys, don't fuckle with Shuckle.

Are people actually debating to use a TM on a pokemon with 17 attack stat?