Hey guys, my 6yr old boy was collecting spent cartridges for his collection today when we were shooting at the range. It's visibly close to a .308 but definitely longer. Put the caliper on it & is way different than.308. Significantly longer & definitely wider. Rim of case is more wide as well. Also, I'm sure the case is definitely steel & Not brass. My boy asked me what it was & I said 308 buddy, then I looked closer & Im wrong, however I do know some shooters that can probably answer our question......