Ken Campbell, Iowa wrote: what are your sizing and crimping dies and techniques ?
does the lee trimmer index on the shoulder ...or on the case base ?
how much headspace do your baseline cases have...after a few firings, the cases should have zero headspace, ....so ...geepers ....what is growing ?
interesting. ken
Ken: Sizing is Lee Collet Neck Size Die in 7.62x39 modified with a .303 Brit Mandrel to fit my bullet size .3125” Standard die setting to instructions.Crimping Die is Lee Factory set to return case mouths .001” smaller than neutral case mouth size before case mouth flare and bullet seating. The brass ia very minimally worked. You can see the fine line the Lee FC die makes on the brass in the photo, but it is little more than just a line from a - .001 Crimp to close case mouth flare. The rifle is a single shot, I don't need a crimp, but I don't want a flare left. The flare is + .003” and will skid the chamber if left there.
The Lee Zip Trim indexes with the contact of the cutter gauge pin through the flash hole and against the flat plate behind the case head that the 3 Jaw Chuck of the trimmer draws the case head too. Deformed protruding primer pocket edges or dirt can give cases a false long reading but I am not getting deformed case-heads or primer pockets . Case-heads check flat visually and are not tipsy on the case-head flats.
The cases are fully fire-formed from 5 cycles of full power loads and 4 subsequent cycles of the light loads I'm testing. Cases were checked and trimmed every cycle of full power loads also. I believe the brass is full head-space as practical in size.
I cannot determine where the cases are lengthening other than overall length and this is only about .001” at most ... but it is happening!
If these were full power loads I would be expecting normal neck length extruding from the fire power.
There is an error somewhere, but it is only .001” at most presenting at the length overall of the brass from case head flat to case mouth as that is all the Zip Trim monitors and trims.
I am clueless on this one.
Gary