Personally I'd gauge itby how they live their lives, just the same as everyone else. But in this list, (things you won't believe are in the bible), [ranker.com] point 21 from this is pretty relevant: if they are Christian then they should love others as they do Jesus...so if they'd take a bullet for Jesus they'd do it for you...if they're true Christians.

They are whacked if they do. lol

Right or Wrong I think the idea has some merit, especially for the religious fanatics, regardless of their particular sect.

It's a logical guage. If they truly believe the claptrap, they wouldn't. According to their legends, God is omnipotent and omniscient so would not be harmed by a mere bullet, no matter how shiny. A mortal incaarnation of said god could possibly be harmed, but, meh, they're a dime a dozen.

It's certainly a good way to gauge their lack of faith in his omnipotence, since an omnipotent being could not be harmed in any way, let alone by a bullet.