Thanks everyone... some very good points raised.
D-Mon
In my enthusiasm to post my results, I didn't acknowledge your help with the methodology
Regarding neck thickness, the .300/221R made from .357 Max brass measures 0.010" vs the .300/221 case made from old reformed 223 Win brass measures 0.0115".
.300/221 cases made from 221 Fireball brass measure from 0.085 to 0.0115" (they definitely need neck turning, I'm not surprised at the lack of concentricity given the extreme sizing from .224" to .308").
Stands to reason the .300/221 case has a thicker neck, as it is originally part of the shoulder.
These measurements are taken with a Mitutoyo digital vernier, not the best for measuring neck sizes... I'm getting a digital pipe micrometer soon, which will be far more accurate.
Jon
I sectioned both a .300/221R (discarded non-annealed case) and a standard .300/221 FB, and there is indeed a slight difference in case thickness at the head. Measured as best as I could just above the web, the .357 Max case wall thickness is 0.0395" vs 0.0400" for the .300/221 FB created from Winchester 223 brass.
Note the amount of burrs around the flash hole on on the Remington .359 Max case!
The biggest difference was in the case head thickness just below the primer pocket... the .357 Max brass is MUCH thinner than the 223 brass at 0.0480" vs 0.0780". The radius between the head and the case walls was also different... the .357 Max case was exactly R1.0mm vs R1.25mm on the 223 case.
Not sure how much difference R0.25mm and 0.005" wall thickness will make in overall case strength, but the much thinner case head below the primer pocket is a worry. It would be VERY wise not to exceed moderate .300 Whisper supersonic loads
Redtazdog
Thanks for the links... I'm sure I'm just reinventing the wheel with this .300/221R cartridge...
I'll see if BellM have a standard reamer print, but I'll also have some more fun designing my own
BoS
Threaded Mode