All it says is ".300 5-Round Mag" and "This is a five-round magazine for our .300 detachable magazine assembly. Cartridge overall length allowed is 3.700″."
No dimensions listed. Also checked on midway, where he also sells them.
So I'm guessing its for the RUM or H&H, judging by the OAL listed.
I actually have already annoyed the guy enough with questions, he told me that it would fit 375 H&H which is what I need it for.
Was hoping someone had one lying around, but I guess I could call and ask on a weekday.