empty cases for trigger work

Read an article on how a person needs to balance an empty case on the top strap while practicing their trigger pull. 

With loyal 629 in DA its really easy.   IN DA, slow or medium, the case flies off. But when placed on the barrel serrations,,, it just stays their.

is that a result of big heavy gun, crappy long trigger pull,,  when i do it, i only notice a muscle moving in my inner elbow.