the thing that most people fail to understand about unboxing: it is not the crate, nor the key that determines the chance of unusual, but a remote server that 'rolls the dice' and decides, at that exact moment and on a case by case basis, whether or not you will unbox an unusual. then, it rolls the dice again, determining the hat/effect (so 2 more rolls) if it has already hit the 'unusual' number of the dice roll (1 out of 100, like rolling a 1d100 and hitting the number preselected to be the unusual). in other words, it is all luck, and there is no crate that grants a better chance of unboxing an unusual than any other.
during the week of christmas last year, there was (supposedly) a 4x increase in your chances, but that, again, has nothing to do with the crate or key itself. i did witness many more unboxes of unusuals that week, so that rumour was likely true.
people either get lucky, or they don't. crate number is ignored in all but the 'losing' 99% of unboxes, where it is used to determine which pool of items to 'roll' from.
i hope my explanation is helpful to some people, and if anyone can verify my statements, it will convince people not to worry about things like crate number, and prevent people from going out of their way to buy series 1 crates, etc, in hopes that it will give them an edge.
and, to specifically address the question, i am going to take a stab here and say that someone misheard, or misunderstood something they heard: the chances of getting a hat may very well be about 1 in 4 in the sniper crates (dunno, don't have one handy to look at right now), but that is not the chance for an unusual. if 1 in 4 crates produced an unusual, those crates would cost an earbuds each in the trade market lol. there is no merit at all to that claim, sorry.