I have heard rumors that if you do it right before the sight updates, theres a higher chance, or to hit at one of the lines when you spin. I think all of this is total bull sh*t.
it is all probability, if someone just got a weapon that you wanted, chances are very high your not going to get another one, also, if the weapon is at the top of the list, that is also going to not have a high probability of winning because their are many people buying that crate