How to do Armor Piercer after vertical grapple?

I see a lot of people doing a vertical grapple into Armor Piercer.
How do you do it? Is it just a strict timing? Which grapple followup do I use (L or H)?

Also, when doing a snapback after a grapple, do you do it with the grapple H followup? And is it just a really strict timing too?

armor piercer after up grapple is character specific and universal in any x-factor (not sure about larger characters!)

for snap back you can do either L follow up in the corner or H follow up anywhere on screen.

L follow up i find way easier than H follow up because the later is a one frame link!

Ah okay. Thanks for that. Is the snapback after grapple also character specific? I find I was able to do it on Doom, but not Hulk.

L follow up hits more characters due to being one frame faster than armor piercer but the H follow up should work on everyone.