The .270 Win is true 7mm - not the 7mm-08 or the 7mm Rem Mag.

Surely you jest!

The calibre of a rifled barrel is measured by bore size... bore size is not bullet or groove diameter, it is measured from top of land to top of land.

7mm and .270 both fit this description of rifled barrel calibre.


Cartridge designation has no rule of thumb...
 
I've often said that I don't see why the .284dia exists in North America when we already had the .277 dia. I've always though that the legitimate step down from .308dia was .277.
The Europeans stepped down from the .323 to the .284, and that makes some sense, as those are 2 very different diameters with 2 very different applications. In North America, we seem to want absolutely everything in between, and we make mountians out of the smallest bullet diameter change. We also seem to think that 100fps will allow a bullet to bounce off of an animal.
Mike
 
mike shickele said:
I've often said that I don't see why the .284dia exists in North America when we already had the .277 dia. I've always though that the legitimate step down from .308dia was .277.
The Europeans stepped down from the .323 to the .284, and that makes some sense, as those are 2 very different diameters with 2 very different applications. In North America, we seem to want absolutely everything in between, and we make mountians out of the smallest bullet diameter change. We also seem to think that 100fps will allow a bullet to bounce off of an animal.
Mike
Click to expand...

not that easy for european because there is a least two 8 mm one in .323 the other in .321 called the short 8 mm or 8x57J then cam the 8x57JS ...

confusing isnt it ...
 
medvedqc said:
not that easy for european because there is a least two 8 mm one in .323 the other in .321 called the short 8 mm or 8x57J then cam the 8x57JS ...

confusing isnt it ...
Click to expand...

Actually, the "other" 8mm diameter is .318; that was the 8X57J. The .323 diameter version is the 8X57JS. This is the more modern version. The 8X57J was chambered in 1888 Mausers, and some 98 military/commercial rifles.
Most european rifles are in generall one or the other of these diameters, though there is some ambiguity. Generally speaking, the older rifles in the older diameters are in .318, and the "newer" rifles in the newer calibers are in .323; though, I would put money on the fact that any commercial 8mm post about 1930 is in .323, as it became the standard. It's much like early on in 30cal history there was a bit of ambiguity.
Mike
 
If the barrel is bored to 7mm (.277) then rifled .0035" deeper per side, we get a bore diameter of .284" Both diameters .277" and .284" can be properly referred to as 7mm, just as .308, .310, & .311 bores are referred to as .30. Now how the Brits dubbed the 7X57 a .275 Rigby is curious; perhaps their rifling was .0045" deep, or maybe ".275 Rigby" just sounded good to them.
 
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