Gen 4 G20: What's everyone's take on PRE in an AM barrel? My max observed  is .0090 over new (Starline) @ .4300

Other than measuring for the sake of measuring, my gut is saying I shouldn't put much stock of the results.

PTII is looking more and more like a reality.

I think you are saying that Pre Measurements vs. the expansion...is it useless?  Well it is sometimes necessary to check where the SMILE may and if it starts with upper end loads.

Underwood's new 10mm brass usually starts at 0.4220"
Chambers can range various internal diameters from 0.4270" - 0.4340"
Knowing the inside dia. vs the max expansion, tells whether the expansion exceeds the chamber itself!
Yes even tighter AM barrels with upper end loads can exceed the dia of chambers and that can show where the feed ramp is on any barrel if pressures are too high.

Best I can measure: LW 5.15" is .4330

Max from this barrel is .4300 - No load has produced any kind of smile.

I've read that .4340 is the max expansion that some will load to. My stock (Gen 4) barrel measures .4390

The max expansion I've realized is .4305 in a Lone Wolf barrel, it's chamber measures .4340.

The same load that produced .4290 in the LW produced .4340 in the stock barrel.

Head hurts...

Quote from: Benchrst on December 07 2015 09:46:25 PM MST
I've read that .4340 is the max expansion that some will load to. My stock (Gen 4) barrel measures .4390

The max expansion I've realized is .4305 in a Lone Wolf barrel, it's chamber measures .4340.

The same load that produced .4290 in the LW produced .4340 in the stock barrel.

Head hurts...

The brass probably fills to capacity when at max pressure and temperature, then when it cools it probably shrinks a little.  (Wild guess)

By you numbers it shrinks .005 after cooling