HELP! Cant do air magnum to save my life!

Hey guys Ima noob lol. I got MVC3 day one and was horrified at the deep learning, got UMVC3 nearly 7yrs later and tried on ps3 and was overwhelmed. After spending over 1,000 hours playing Killer Instinct for xbox one Im alittle tired. So I got UMVC3 for pc and now playing the EX version! I LOVE it. I`ve put 40hrs into the lab trying combos, I can do some stuff, I want to learn chris, but I kant seem to nail the air magnum. Its not when you just jump and do it for an OTG.

Its when you launch them into the air, knock them down with S. Then as your falling down chris does the air magnum and causes the opponent to pop again. Ive spent 40hrs in the lab trying to do it, I can barely do it. Heres my main problems.

-Chris says “suck it!” it gets to the point where he drops after S. and has his magnum out but he doesnt have enough time to pull the trigger.

-Chris actually ends up shooting the magnum then out of nowhere instantly pulls it out a second time as soon as he lands, causing his opponent to tech role.

-As Chris is falling down he pulls out his knife and lands. :bawling:

This is causing me to not use chris as much, I can do some stuff with him, but I cant extend any solo combos without that dropping air magnum. I want to make a resident evil mahvel team on UMVC3 EX. But alast I cant :frowning:

Any help guys? :anguished: