Which calibers fall into the category of medium bore?
What is the start and cut-off point?
RV

Roughly, 26 to 36. There will be some argument of course, but this will work as aguideline. - Dan

Traditionally , the medium bores were considered those between 30 caliber and 40 caliber. The .375 s are for sure medium bores , except here on AR (grin) .

And I think anything below .30 should be considered a small bore........

My personal thoughts are, 30 caliber and below are small bores. Medium bores are 8mm on up to 40 caliber. I still haven't come to terms with whether the 40's are heavy medium calibers, or light large calibers. 45 caliber and up are certainly big bores.

I suppose this should be qualified by the fact that my centerfire rifles consist of a 350 Rigby, 458 Lott and 500 Jeffrey. One of these days I'll pick up a 300 mag so that I'll have a small bore The wife does have a 6.5X55 and a .308, so there are some small bores in the safe.

I believe Saeed considers 6.5mm on up as medium bores, and 375's as the beginning of the big bores. It's his site, so I will bow to his preference.

Right under Medium Bore Calibers, it says:

"From The 27 To 366 Caliber Rifles"

I think John Taylor tried to quantify this in his two books on African rifles and cartridges. I tend to think in African terms when referring to Small, Medium, and Large bores.



In Big Game and Big Game Rfiles he listed

Small: anything under .28

Medium: .30 - .375 (or less than .40)

Large medium: .40 or greater but less than .45

Large: .45 or greater

There was also a Miniature category that had a energy cut off point but I can't remember the number now.



In African Rifles and Cartridges, he listed the medium bores as starting at .318 instead of .30 (if I remember correctly). Although he doesn't list the catridge specifically by name when listing .318 as the floor, I believe he was referring to the .318 Westley Richards which is actually .330". All of the above is from memory as I don't have the books handy at the moment to double check.



.30 caliber seems to be the one that straddles the fence with a lot of people. Some put it in the small bore category while some put it in the medium bore category. But, there are no .29 caliber cartridges (at least common ones) and the gap between .28 (7mm) and .30 seems to be a good cut off point between Small and Medium, at least for me. Leaving aside specialty bullets, the heaviest .28 caliber bullets are 175 grains. The heaviest .30 caliber bullets are 220 grains. That's a pretty good size jump. That's why I like to include the .30 calibers in the Medium category.



Of course, energy developed should be a criteria also. For example, I wouldn't think of the .30-30, the .32 Win Special, or the .35 Rem as medium bores in the African sense. Examples that are medium bores in Taylor's context: .30-06, .300 H&H, .318 WR, .338-06, .338 Win Mag, .35 Whelen, 9.3x62, .375 H&H.



Just my ramblings....

-Bob F.

Perhaps I should have expanded on my post. I look at the classes of game that would be hunted with various groups of calibers. I look at the 30 caliber and under in what I tag as deer rifles. These are rounds for use on thin skinned non-dangerous game under 500#'s. They can certainly be used on larger game, but aren't ideal. I really can't see any game where I would consider a 30 caliber noteably more gun than a say a 7mm.

When you jump up the next class of game, medium to large thin skinned game, ie elk and moose, and the smaller bears, then the 338 through 375 come into their own, this is the medium bore class.

When you look at thick skinned and larger dangerous game, then the heavy medium and big bores are worth paying the recoil piper.

well, since the 8mm rimmed french lebel round was/is considered the first smokeless "small-bore" military round, then i'd have to say the mids start on the far side of .323 and go up to 45, with the big bores starting there. but what do i know? i've never owned a mid-bore, by my definition, and i have owned all of one "big bore," a .45-70 marlin, and it was so unpleasant to shoot, i sold it. but i will, some day, have me a .338 win mag or a .375 h&h bolt gun. i think proper stock design will take care of any recoil gripes that i had with the marlin.

I kind of relate it with what is suitable for small, medium and large game. Around here that means gophers to coyotes (small), deer sized game (medium), and so on. The subcalibers on up to roughly .25 are what I see as more or less the "varmint" class, or small game/bore. Places in Africa have established the 375 as the minimum for dangerous game, which I think makes a good cut-off for medium to large, with all inbetween being that of the medium variety. Although around here a .35 caliber is considered a large bore by the majority of hunters.

I suppose like a lot of things, the viewpoints can vary with the geography, available species and popular methods.