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Brass 'Bloats', the sides bulge out when fired making the length shorter, not longer.
This is particularly the case with 'Semi-Auto' chambers since they are 'Loose' to facilitate the auto-loading process.
Two things to remeber here,
1. Neck length isn't important as far as accuracy goes.
The primary function of the neck is simply to hold the bullet more or less centered with the barrel.
Secondary function is a gas seal, but the shoulder does most of that work.
2. As you push the case sides back in where they belong, and he shoulder/Datum Line back where it belongs to headspace properly,
The brass has nowhere to go but 'Up' into the top of the die.
The higher pressures you run, and the softer brass you use will determine how much the brass 'Grows' (how much brass from the side walls migrates forward) with repeated sizing/loading/firing.
With .223/5.56 'Range' brass, I trim to MINIMUM while I'm swaging primer pockets etc on he second loading and never touch it again.
Since I'm not loading super hot for a bolt gun the brass never needs to be trimmed again.
The one thing that precise trimming is needed for is CONSISTANT crimps when you use the seater/crimp dies.
Collet style 'Factory Crimp' dies don't care what length the brass is within reason,
But a seater/roll crimp die MUST have the same length cases to work properly.
(Hense the popularity of the 'Factory Crimp' collet dies, nobody likes trimming!)
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