Each shot / reloading cycle, they shrink a little more and do not recover as far. Hard to say where that lost length is going to. In the cases I've resized, the majority of the resizing effort resides just above the web, but I believe that's just due to the wall being thicker there. Meanwhile, its getting harder to get the same neck tension each subsequent reload without cheating the taper crimp in a little further each pass. I have an inertial puller set up on a pendulous arm that I drop onto concrete from a specific height to gauge the number of strikes it takes to dislodge a specific cartridge. Yeah, I need a life... Anyway, with the once fired brass, I could use a taper crimp of .478 to get a tension that requires 12 inertial puller drops. After 4 reloadings, I now need it set to set the taper crimp to .476 for the same tension. Something's changing...
At the same time, the brass keeps retreating. Here's what I've observed so far:
1 Fire Unsized length = 1.693-95
2 Fire Unsized length = 1.691-92
3 Fire Unsized length = 1.688-90
4 Fire Unsized length = 1.685-87
5 Fire Unsized length = 1.682-84 (that's from a load of 25 brass I just took out of the tumbler this afternoon)
I suspect this last load will no longer resize to a minimum of 1.690, but I haven't tried processing it any further yet.
Bob, I've cross-sectioned a case to actually look at the wall from top to bottom under the stereo microscope. I found no abnormal thin spots.
Up until now, I was mixing my brass together after processing. I d put a micro-dot on the head each time I reload it with one of those push-punches using a reduced strength spring. I had once through fourth fired brass mixed together and I suspect that might be why in some test passes, my SDs were wide. I'm very thorough in my processing and I scale every load. Yeah, I need a life...
If you're new to reloading, here's my step list for the 450b. I keep brass in ziplocs with a sticker on it that has a check-box for each step, so they don't get mixed up.
1: Tumble in clean walnut media (little pieces of dryer sheet mixed in to pick up the dirt and de-static the media)
2: Inspect with a magnifying glass for problems (one of those headband magnifiers from harbor freight)
3: Lube (imperial), decap/resize.
4: Wipe off excessive lube
5: Clean the primer pockets with a
cutting uniformer (kills two birds with one stone)
6: Uniform the flash holes (one time affair)
7: Lightly burnish inside of necks with stainless steel bore brush in drill (easy does it)
8: 8 minutes in the ultrasonic cleaner (dish liquid/vinegar/water mix) blot, then oven dry
9: Prime, microdot the head to track the number of reloads
10: Measure length segregate by length (new step)
11: Expand/flare mouths (just a hint of the flare)
Note: Lately, I've adopted the the stance of not doing this step and found it yields slightly more tension. Tension is paramount
12: Scale the powder load (I use a Lyman 1200 DPS2, checks perfectly to my beam scale)
13: Seat bullet while DPS2 is dropping next load (the timing's prefect)
14: Taper crimp
15: Optional Lee FCD crimp. The jury is out on this step. Scars the brass with not so obvious benefits so far.
I may have forgotten something. Family is grousing at me to watch a movie with them. Yeah, I need a life...
Hoot