Just to be a little more clear; yes, any particular fired straight wall case will be shorter in OAL before it's re-sized, however that same case after re-sizing will generally be a little shorter OAL than it was before it was fired in the first place.
I'm not trying to be pedantic, but I'll put the following out there for the benefit of the guys who haven't be re-loading for long: (it's worth what ya paid for it
It helps me to understand this by thinking about the slight taper that virtually all "straight wall" cases have to help them chamber easily. When fired this taper is blown out to the chamber dimensions releasing the bullet. When you re-size the case you are squeezing that brass cylinder back down to a slight taper by forcing it into a cone shaped die. That action pushes the brass back toward the case head a little bit each time, resulting in a slight shortening.
In a typical bottle neck case the gas pressure against the interior of the case shoulder pushes that shoulder forward until it is stopped by the shoulder of the chamber, and then in the resizing process the neck expander ball is dragged through which also pulls brass forward. These two actions tend to make the brass flow forward into the neck, and the case gets a little longer each time it's fired and re-sized, so trimming is required. Neither of those actions occurs in a "straight wall" case, so there is nothing to counter the compression of the brass toward the head by the sizing die.
Common problems with multiple uses over time in a bottle neck case include head separation caused by the brass being stretched thin just in front of the case head, because that brass moving forward has to come from somewhere, and overly thick case necks caused by the brass flowing into the case neck.
Common problems with multiple uses over time in straight wall cases include case mouth splits from the case mouth being repeated expanded and then squeezed back down, and case OAL becoming too short from repeated resizing.
Brass "flow" from the pressure in the chamber upon firing is something that occurs somewhere in the 60,000 psi and up range, depending on the particular lot of brass. As most straight wall cases operate well below that pressure level, you're not as likely to see this effect. IMHO Straight wall cases eventually die from more simple mechanical forces as a result of being repeated stretched open and squeezed back down during the reloading process.
In the .450B we are adding one more mechanical process with the "body" crimp. It remains to be seen how that effects brass life long term. In the meanwhile, I am getting excellent case life when compared to most bottle necked cases I load for.
BD