1.039 that puts the bullet right at the shoulder and close to compressing the powder (HP-38) Is my thinking wrong ?
Take another couple of bullets and cases and try that test again with several test subjects. You should be getting a reading closer to 1.075 to 1.080 inches.
I loaded and shot 95 test rounds in my 75 Shadow. The first were at 1.1" and shot fine but a skosh on the light side. I ended up at 1.095" with plenty of margin for OAL error. I like the bullet and ordered 3K.
I may add another .1 grs of powder when my order comes in.
Your chamber 'might be exceptionally short', but I would redo the push test with
at least 5 different spent cases and bullets. Your test sounds mighty short.
You wouldn't be able to use a MG 124 JHP as it's conical nose that tests close the same in my and many other CZ chambers. The Zero 125gr JHP traditional ogive wouldn't meet your test results and preferrences either. Somethings not right.
re "is my thinking wrong?" If you load shorter than the data, you need to decrease the powder load proportionately, so it won't be closer to compressing the powder.