I had purchased some 300WM ammo at a local sporting good store that was on sale. It was Hornady Custom Lite/ Reduced Recoil 150gr SST. Main reason for purchasing was to get the brass for reloading and it was cheap.

I took it to the range yesterday and shot 1 box. On the second shot, I noticed the recoil and rifle report was different. When I ejected the shell I noticed it looked like the neck had came off. I then disassembled and inspected the rifle for the missing piece. I didn't see anything so I tried chambering a new round which did so and I continued on. It wasn't until today that I was cleaning the brass when I noticed the head stamp on the questionable shot says 7mm rem Mag. I also wonder if I actually shot a 7mm rem mag thru the gun or if they somehow loaded a .30cal in a 7mm RMag stamped casing. I feel like I would have noticed the difference as I was loading each shot individually.

Also all the other proper headstamped brass after cleaning and FL resizing is measuring 2.598. My Hornady reloading manual states max case length to be 2.620 and Min case length to to be 2.615. The latter being what I trim all my brass after each firing. So it appears Hornady has loaded this with brass that is shorter than spec. My question is this normal as this is my first time to shoot factory loaded ammo with the intent of reloading it.

Picture is the 7mm headstamped on left compared to the 300 WM on right. The shoulder measures the same on both.
Thanks,