chamber gauge and resizing questions

I've been playing with three chamber checkers and my barrel to learn the differences.   Fired brass (from my pistol) doesn't fit in the Lyman, is tight in the Shockbottle and Sheridan but does fit in the Kart barrel.   The Kart is the only of the four where it also falls back out by itself.

1) If brass is fired from my pistol and is only going to be fired in that barrel again, is the purpose of resizing the brass to re-establish neck tension below where the expander works the case?  

2) How much can one make up for less neck tension with a heavier crimp - or are the two not really related?

3) Does reducing the outside diameter of the brass, more than the minimal needed, result in more of the firing energy being taken up by expanding the case?  I can't imagine that makes much difference to energy imparted to bullet or any other significant issue

4) Are all chamber checkers going to yield cartridge diameters as the smallest that fits in all barrels, therefore of dubious value when I am only shooting one pistol in that caliber?

Thanks

45acp
1.brass is sized to provide neck tension.   You can size just to where the base of the bullets stops. Sort of like neck sizing. (Old RCBS news letter). This  didnt work, caused chambering problems.   I now size with the thickness of a nickel spacing betweeen die and shell holdder.

2.  Neck tension is primary,  a taper crimp does little to keep the bullet from moving.  The slight crimp helps feeding and chambering by removing the flare/bell.   To much taper crimp may size a lead bullet smaller in diameter, if over done.
Range brass can produce wide variations of neck tension. Bullet pull ranged from a low of 45 lbs to over 100lbs. .002" to .005""

3. Dont know.  Military testing of 5.56 ammo said  there is  4%   difference in case volume between    new and fired.  Case volume would have an effect on pressure and velocity. No idea how much. As long as all brass is sized the same, of the same lot, i dont see a problem. Range brass is not good for accuracy. Imo.

4.  Ammo must fit the guns chamber.  Never used a pistol gage to check reloads.

SAAMI has standards.  The tolerances  show largest and smallest of loaded ammo and chambers. https://saami.org

What does this all mean? Very little till rounds dont chamber. Then  taking measurement may give a clue to where the problem lies.

Two thoughts

One. Full length sizing the shell and then expanding it creates a shelf for the bullet base, if done correctly. Factory rounds in hbwc use a cannelure for the same purpose. In hbwc, it bites into the bullet, for all others, its at the base.

Tigher fit increased pull force which results in higher chamber pressure and velocity.

Three. Spend more time shooting, not wasting it like the rest of us. Smile