nope 
thats not it
.220 Swift.
not 220 swift, but that is a great round!
Is it a 243
nope not a 243
What about a .300 Savage?
not that but getting warmer
.338 Win Magnum
nope not that big
Not a good old .308
na, a bit faster than that
.308 Marlin Express?
nope, no, not that
So faster than a 308, smaller than a 338 and close to a 300? Is it a 30 cal?
Not a 30 cal.
A .257 Rroberts
Close now👍
260 Remmington
Yeh, gotta pay that. 
Where did you get that from?
I just googled head stamp, Lol 
Not 260 rem!