Either way.
You might be interested in the fact that creedmore has a number of spellings .It used to be the name of a major shooting range in NYC ! There were target rifle models with the name also , such as the Remington Rolling Block and Sharps Creedmoor rifles.
They shut down the shooting range and turned it into a mental institution !!
I don't really think there is a "proper" way to say it. There's a proper way to say "Creedmoor"... and a proper way to write it... literally, a proper way. It's a proper noun and should be capitalized.
Yes, it is Creedmoor, named after the old range on Long Island, NY.
From an 1876 article...
"The place was an open, desolate field, with coarse, scanty grass and brambles - a veritable moor. The first owner's name was Creed, in whose family the property had been for generations. Hence by a happy inspiration and coincidence arose the now famous appellation, and "Creedmoor " became the name of the new range,"
All Six Point Five cartridges have been said this way.
Yes, unless you go a bit farther back to when the 6.5mm Mannlicher was known in English speaking countries as the .256, later followed by the .256 Newton. Bore diameter, not groove, which is one reason that when an internet expert slugs the barrel and relates his ".2645" bore diameter", I get a bit touchy. Kind of like the difference between a magazine and a clip, you know.