Something I have always wondered about ... 303 British

[goon]

I loaded up my first batch of 16 .303 British 180 grain Speer RNSP's last night with 41.6 grains of Winchester 760. I tried them all out today and they shoot pretty close to where my sights are looking at 100 yards. I am thinking that working up to 42 grains will probably get me right on target. Gotta get them ready for deer season.

Anyhow, something I have wondered...
I have loaded and shot .308 Winchester for a couple years now. I understand why it is called .308. If you take a bullet for it and measure it in your calipers, it is going to be .308 diameter. Makes perfect sense.

The .303 is actually a .311 or so. Why did they call it a .303?

Something I should know already, but I ain't gonna learn if I don't ask.

 

[Moparmike]

One is measured in the lands, and one in the grooves?




BTW, could someone explain to me the lands/grooves thing? Lands are the "tops" of the protrusions, grooves the "bottom" of the, well, grooves?

 

[Biff]

The answer is simple, but a little odd... The Americans measure bore size accross the grooves, the British measure it accross the lands!

 

[SDC]

Some calibres are measured land-to-land, but others are measured groove-to-groove (or where the groove WOULD be, if it's not directly across the bore). Compared to some of the OTHER "Huh? ***?"'s available in the shooting industry, it's not really a big one. For example, NONE of the handguns we think of as ".32"s actually fire a .32" bullet.

 

[9mmepiphany]

at least it makes more sense than guns chambered for .44 calibre shooting .429 bullets

 

[Mk VII]

when Winchester brought out their knock-off of the 7.62x51 case design they decided to call it .308 Winchester rather than .30 - probably because they already had a .30 Winchester Center Fire. Bit like the difference between .357 Magnum and .38 Special - it has to sound different.

 

[Tony Williams]

I've listed the bullet and bore diameters for the major rifle calibres here: http://www.quarry.nildram.co.uk/Cartridges.htm

The nominal calibre used by manufacturers is often only approximate. The .218, .219, .220, .221, .222, .223, .224 and .225 cartridges all have a .220 bore and a .224 bullet diameter.

Tony Williams: Military gun and ammunition website and Discussion forum

 

[Matt G]

I've also oft wondered why I haven't seen a cheap conversion kit available to shoot 7.62X39 through a SMLE .303. Seems like it'd be easy...

 

[Johnny Guest]

7.62x39 mm in .303 adaptor

Do you mean, something akin to the "Navy adaptor," allowing .308 (7.62x51 mm) to be fired in the .30'06 chamber of an M1 Garand?

Hey, why not?

 

[Sunray]

"...why I haven't..." Not enough demand for one thing. The other is that most American loaded 7.62 x 39 ammo uses a .308" bullet.

 

[Gewehr98]

That requires some rebuttal.

The other is that most American loaded 7.62 x 39 ammo uses a .308" bullet.

For a thread that asked the U.S.-manufactured bullet diameter question over on TFL a couple weeks ago, I measured a batch of Winchester and PMC 7.62x39. Wanna guess what the bullet diameters were? See below, 75 rounds of Winchester, purchased late 1999:

 

[Jim K]

Some calibers are designated by the barrel bore diameter, some by the groove diameter. In breech loading rifled firearms, the bullet is groove diameter so the rifling is actually engraved into the bullet as the bullet is forced through the bore. Groove depth is usually about .004", so groove diameter is twice that, or .008", larger than bore diameter.

So the .30-40, .30-30, .30-'06, .300 WM, .30 Remington, etc., are all named for the bore diameter. The .308 Winchester, .308 Norma Magnum, etc., are named for the groove diameter. The bullets of all measure .308".

The .303 British is named for the bore diameter, just like the .30-'06. The groove diameter of the .303 British is .311".

For marketing purposes, cartridges are often given names that really don't reflect actual bullet or barrel diameters. For example, the .218 Bee, .219 Zipper, .222 Remington, .223 Remington, 5.6mm military, .220 Swift, .22-250, and .22 Long Rifle all use bullets of .224 diameter.

Jim