What is in a cartridge name? (Part 2)

Written by Ballistic Technician Philip Mahin

Last time we were discussing why a 270 Winchester uses a .277” diameter bullet. Before we get too deep into this, we need to put a face with the name. When you hear the term 270 caliber (or 30 cal for that matter), this is referring to the firearms bore diameter. This shouldn’t be confused with groove diameter and I’ll show you why.

Bore DiameterThe groove diameter will be .277” but the bore is .270”. This puts an engraving into the bullet and grips it by the rifling as it travels down the barrel making it spin in flight. Now the 270 Winchester was an easy one. What about the 7.62×51? It can also be called 7.62 NATO or 308 Winchester depending on what chamber you have. The 7.62mm translates to .300” or 30 caliber for a bore diameter and so .308” translates to 7.82mm for a groove diameter. That is also the way Lazzeroni named the 7.82 Warbird. It still uses a .308” bullet but it is a name different enough to not get confused with anything else. But what about the x51 on the NATO cartridge? That actually corresponds to the length of the case in mm and would equal 2.015”. The 30-06 cartridge would look like 7.62×63 in military form and there are others like the 5.56 / 223 that are confused quite often. By the way, the 223 Remington cartridge uses a .224” diameter bullet. The .223” diameter bullets we sell are primarily used in the 22 Hornet cartridge chambered in older guns that actually had a .223” diameter groove. More to come . . .

This entry was posted in Uncategorized and tagged , , , , , , , , . Bookmark the permalink.

3 Responses to What is in a cartridge name? (Part 2)

  1. Bart Bobbitt says:

    As the wind speed above the line of sight is higher than in it, I wonder how difficult it would be to incorporate it into Sierra’s ballistic software. A chart I made showing it is shown in this link’s site:



  2. Bart Bobbitt says:

    Oops, wrong link. I’ll get the right one.


  3. Bart Bobbitt says:

    Link to wind chart


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s