Small, Medium and Large Bore: Thoughts on a Metric Definition

[gzr]

Was thinking about what constitutes a small, medium or large bore these days in context of modern cartridge capabilities even in older case designs, and in context of what's generally available today. Why not:

Up to 6 mm (0.236 in): Very Small Bore
6 mm (0.236 in) to 8 mm (0.315 inches): Small Bore
8 mm (0.315 in) to 10 mm (0.394 in): Medium Bore
10 mm (0.394 in) to 12 mm (0.472 in): Large Bore
12 mm (0.472 in) and up: Very Large Bore

I think this shows pretty good general accord with traditional nomenclature around Imperial calibers, and also puts some nice round Metric numbers on those traditional classes while elaborating at the small and large ends. What are your thoughts?

 

[grand veneur]

The classification of A-Square seems to me better, because the cartridges caliber .375 are to be regarded as the last of the medium bores. From practical personal experience I can confirm that there is a clear difference between cartridges caliber 9,3mm or 375 and cartridges caliber 416 in terms of recoil. In all cases, the difference is much greater than between cartridges caliber 300 Magnum and cartridges caliber 9,3mm or 375.

10mm and above is more likely to be counted among the big bores, whereby that's right, one should also differentiate in this class. The cartridge 500 Jeffery is no comparable to the cartridge 416 Rigby for example. Taylor's classification in his book seems therefore more practice-oriented when it comes to the big bores.

A-Square, Rifles-Ammunition-Bullets 1995

 

[grand veneur]

The caliber classification we are talking about is related to hunting, especially Big and Dangerous Game hunting in Africa.

In hunter circles where one primarily hunts its native game, species that are often much smaller than the African, there is often a completely different classification and everything that goes over 8mm is already considered as an big caliber. By rifleman's, big calibers are already cartridges like the 7,62x51mm NATO, in Europe in all cases.

 

[gzr]

The classification of A-Square seems to me better, because the cartridges caliber .375 are to be regarded as the last of the medium bores. From practical personal experience I can confirm that there is a clear difference between cartridges caliber 9,3mm or 375 and cartridges caliber 416 in terms of recoil. In all cases, the difference is much greater than between cartridges caliber 300 Magnum and cartridges caliber 9,3mm or 375.

10mm and above is more likely to be counted among the big bores, whereby that's right, one should also differentiate in this class. The cartridge 500 Jeffery is no comparable to the cartridge 416 Rigby for example. Taylor's classification in his book seems therefore more practice-oriented when it comes to the big bores.

A-Square, Rifles-Ammunition-Bullets 1995

Nothing in your post seems to contradict the categories I have set out. The 2mm increments actually seem to agree with Taylor because:

1. .236 (6mm) to .315 (8mm) small bores coincide with Taylor's 'light rifles'.
2. .375 up to .394 (10mm) are indeed the last of the medium bores. A .318 Westley Richards would be the start of the medium bores.
3. .416 is agreeably in a different class in my structure: large/big bores from .393 (10mm) to .472 (12mm) in accordance with what you pointed out about recoil.
4. 500 Jeffery is differentiated from the .416 Rigby, because the 500 Jeff is included in the >12mm (>0.472) 'very large bores', whereas the .416 is a large/big bore, as would be the .404 Jeff

Could you point out where my schematic contradicts your post about Taylor? Perhaps I missed it. For now I think it only expands upon it, and puts it in nice 2mm intervals that everyone can remember.

 

[grand veneur]

I don't know cartridges caliber between 375 and 408, the latter is more to be classified as a 416 in terms of recoil and working in practice than as a 375, and here we are with the classification of Taylor.

 

[grand veneur]

As for the Big Bores, Taylor divides them into Large Bores and Large Medium Bores, where he also sets the limit around 12mm.

 

[AZDAVE]

7.62 and smaller = small bore
8mm-9.5 = Med bore
10mm and up = big bore

 

[375 Ruger Fan]

Doesn't the 6.5 CM identify as a medium or big bore?

 

[mdwest]

Doesn't the 6.5 CM identify as a medium or big bore?

It identifies as a non fat soy latte bore…

 

[Hunter-Habib]

<.243 (Varminter)
.243- .275 (Small Bore)
.275-.318 (Medium Bore)
.338-425 (Medium Heavy Bore)
.450-.500 (Heavy Bore)
>.500 (Stopper)

 

[mdwest]

I dont get too wrapped around the axel on "bore"... I look more at what a cartridge's capability is rather than how wide (metric or imperial) the projectile is..

there are .22's that have more ballistic capability than some 30 cals..

and there are 338 and 35 cals that have more ballistic capability than some 40 cals..

i.e. a trapdoor 45-70 is awesome (1800 foot pounds of energy).. and would be considered a "large" bore by most.. but.. it has neither the range or the energy (3500 foot pounds) of a .35 Whelen (mid bore)..

For me it all depends on what it is I am trying to accomplish (hit hard at close range? accuracy at mid range? hit hard at long range? minimal pelt damage? etc..etc..).. Once I have established that, I'll pick an appropriate caliber and cartridge.. (while never considering whether the rifle is a small, mid, or large bore)...

 

[gzr]

I dont get too wrapped around the axel on "bore"... I look more at what a cartridge's capability is rather than how wide (metric or imperial) the projectile is..

there are .22's that have more ballistic capability than some 30 cals..

and there are 338 and 35 cals that have more ballistic capability than some 40 cals..

i.e. a trapdoor 45-70 is awesome (1800 foot pounds of energy).. and would be considered a "large" bore by most.. but.. it has neither the range or the energy (3500 foot pounds) of a .35 Whelen (mid bore)..

For me it all depends on what it is I am trying to accomplish (hit hard at close range? accuracy at mid range? hit hard at long range? minimal pelt damage? etc..etc..).. Once I have established that, I'll pick an appropriate caliber and cartridge.. (while never considering whether the rifle is a small, mid, or large bore)...

Sure and I agree. But a .45 ACP is still a large bore and a .500 S&W could be a very large bore, though you probably wouldn't want to stop an elephant with either. Qualify with 'big bore pistol' or 'very large bore revolver'. Is a 10mm auto a 'big bore pistol'? Some in Alaska carry them for bear protection...

I think the whole bore size category thing should be about bore size rather than application. To use an absurd example, one would never think of a 250 grain .243 as a 'medium bore', even if it did have the same bullet weight and game dropping capability as a .338 Win Mag.

Also about the fact that no bullet diameters exist between 7.62mm and 8.00mm, or .375in and .394in: Doesn't matter, still covers the cartridges that do exist! Or any new ones to fill in the gaps for that matter.

Fun topic for mental machinations. I like the 6-8-10-12mm increments for ease of memory. <6mm could be called 'varminter' as well as 'very small bore'. Most cartridges <0.236in are used for varmints, though I do acknowledge people sometimes hunt deer with .223 etc.