Ok, I snapped a picture of few .357 Sig wwb fmj and federal jhp casings. These I collected from the pool of 50 rds of wwb and 50 rds of federal, both ran flawlessly, and the weapon if anything was dirtier as I shot these last.
If anyone can observe something weird on those strikes in the pic, let me know. To me they look normal.
Again, unfortunately I did not collect elite performance casings but out of almost 200rds, only two were duds.
It is just something I've never experienced before. I pulled the trigger and hammer dropped and nothing happened. On one I cocked the hammer back and squeezed the trigger and that round then fired as normal.
On the other dud, when the hammer fall and nothing happened, obviously slide didn't move, I just squeezed the trigger and it fired as it should.
This happened on two different mags (had enough sense to at least test that),

so I'm pretty sure it is not mag related.
The last two mags of federal jhp, I rapid fired two mags back to back, no issues.
I will just chunk it as bad ammo, as others have pointed out, and I'll stay with wwb for range and federal for sd.
That's two duds out of I believe 298 rds I fired today. I think it is hip worthy.
Side note, incredibly accurate and I had no other issues at all. Just those two weird ones...
