cals. and mm????

[boatguy]

^9
Can someone please lead me in a dirrection to learn calabers and how they are measured, and milameters and why/how are they used, how do you convert one to another. Just basicly a 101 class on all this. For some reason I just can't grasp it, I my be nuking it, I don't know, just sounds so complex to me. Thanks...

[Custom Glock Racing]

Caliber is the diameter of the projectile measured in decimal inches or milimeters.

9mm = .355 cal

[boatguy]

Yea, that much I know, I'm looking for a site that goes into detail about all of this, know of any?

[VN350X10]

Let's start with the basic math.....

1mm = .03937"

That's the easy part.....

Now, when you get into the actual calibers is where it gets confusing.
Some ctg's. are called by their true size, eg. .243 Win., .308 Win., .264 Win.Magnum, .458 Win.

MOST ctg names aren't the true size.
Just for a few examples...
.22Hornet
.218 Bee
.219 Zipper
.220 Swift
.221 FireBall
.222 Rem.
.223 Rem.
.224 Weatherby Mag
.225 Win.

Of these, only the Weatherby is correct...ALL of these use a bullet diameter of .224" (old Hornet used .223", but newer ones use .224")

The various 6mm/24 calibers, 30 calibers, et. al. are just as bad, the new Lazzeroni brand of rifles & their propriatary ctg. names are another series, as they go by groove diameter to name the ctg. size, but they use metric dimensions, the British method usually refers to groove size (but not always), some of the older American ctgs. refer to caliber & powder charge,eg .38/40 (not really a 38!), 44-40, 38 Special is a .357" bullet....
I hope you kind of get the idea.....there is NO set, specific, common nomanclature that REALLY tells you what a given round is.
Best bet-study various reloading manuals & reference books.
Possibly the best single book would be "Cartridges of the World". It's now in it's 9th or 10th edition, & is the best single book for this type of information. I collect firearms books & have a complete set of them, along with a complete set of "Gun Digest", another excellent reference book.

Yes, it's confusing. I try to learn something new every day. Beats the boredom of watching T.V. !!!!

Hope this helps more than it confuses.

shoot safe

uncle albert