what is the 8 in .308?

[42769vette]

this may sound like a dumb question but its one i really dont know the answer to. i know the first 2 numbers are the caliber but i never know what the 3rd number is. like a .223, what is the 3 i know the actual bullet is a .224. what is the 06 in 30-06. so on and so forth i think you get the question its puzzled me for years

 

[OneBadV8]

ummm... usually its just the size of the bore. so they round a little. and they are all different sometimes with the hyphens.

the '06' in .30-06 is a .30 caliber made in 1906. But with the .30-30 the last 30 is the grains of black powder used in the catridge. a google search usually gets you close.

Clear as mud?

 

[jblomenberg16]

It is a .30 caliber, but the .308 is the bullet diameter.

 

[jblomenberg16]

Not to be confused of course with the .303 Brit, which is a .311 bullet, like the 7.62x54r, and 7.62x39.

 

[42769vette]

Not to be confused of course with the .303 Brit, which is a .311 bullet, like the 7.62x54r, and 7.62x39.

thats my point. i dont think there is a rule of thumb on the 3rd number. atleast not that i can figure.

 

[kludge]

.308 as in ".308 Winchester" is the bore diameter across the grooves.

.303 as in ".303 British" is the bore diameter across the lands, while the groove diameter is .311 and thus uses .311 bullets.

To make things even more confusing, the 7.62x39 Russian traditionally uses .311 bullets and has a .311 bore. However early Ruger Mini-30's were built with a .308 bore (to the grooves) and there was a warning not to use surplus ammunition - but to use domestic ammo made with .308 bullets.

My 7.62x39R die set came with two interchangeable neck expanders, one for using .308" bullets and one for using .311 bullets.

Many people who build a bolt rifle for 7.62x39 get a custom barrel with a .308" bore so they have a much better target and hunting bullet selection. (Yes thay can be VERY accurate - the parent case for the 7.62x39 - the .220 Russian - is used for the .22 PPC and 6mm PPC cartridges and 6.5mm Grendel. fireball168 uses the same parent case for his .358 Gremlin, necking up Grendel or 7.62x39 brass.)

 

[jtmarine1911]

There is NO standard when it comes to how a cartridge gets its name!

There comes a lot of confusion as well when you throw Metric designations into the mix.

Some cartridge designers use a combination of the bullet caliber and a manufacturer name to designate it and some just got close to the caliber.

Matter of point: I was reloading some 7.62NATO brass for my AR-10, I was at work on the PC looking up some FMJ bullets from Midway and an engineer inquired what I was doing so I explained. He stood and watched me for a few, messed with his phone a minute, then asked why I was looking at .308" diameter bullets. He then said that .308" comes out to 7.82mm and would not work, so I proceeded to inform him that 7.62NATO was just a refernce name. and used the .357 Mag and .38 Spec as an example.

 

[jlm223]

Really don't have anything to add, just wanted to say I really enjoy reading your post, that's some interesting stuff.