There is no such thing as always in genetics. The biggest factor is the genetic makeup of the mother, which isn't always the easiest thing in the world to determine.
I think it is possible to refine out a line to where it throws something consistently, and in general if a breeder has a nice blue bar sire, and a female that is from a blue bar sire, there is a good chance that you'll have some blue barring in the baby you buy.
For example, I have a male with solid blue barring, not a speck of red. He's the 3rd generation of Blue Bars from that line. I have a female from a nice blue bar line from a reputable breeder, I have photos of her blue bar siblings. I'd be pretty confident that there will be some blue bar offspring if I pair them together, but wouldn't be surprised at all if some red came up.