Im not sure this is the right forum, but could someone tell me what the cannelures that are found on some metallic cartridges are for.

Secondary resting point for the origional bullet, typicaly lead wadcutter types. Not of any importance as far as reloading goes (assuming that's why your asking).

Just curious really.

I always thought the cannelure was there to lock the jacket to the lead core. It could realistically go anywhere on the length of the projectile to acheive that function , but has been conveniently placed to coincide with the point at which the case mouth finishes when the projectile is seated - allowing case mouth crimpimg to work more effectively .

Or something like that anyway....that is a simplified reason for it as I see it anyway .

muzza
The canalure on the "bullet" is there to act as a crimping groove/core retention, as you mentioned. However I beleve the gentleman is refering to the canalure you sometimes find about 1/2 way down streight wall pistol cases like the 38spl, 45ACP etc. But I could (as often happens) be wrong.

Duh-

you are right . Too many other things rolling round in the small brain dept.....

The case cannelure is an id thing on some calibres isnt it? Like - match loadings . And , as you say , on straight walled pistol/revolver rounds it serves as a seating depth guide , as well as looking pretty...

I shall attempt to get more sleep tonite to avoid further obvious acts of stupidity..

It prevents the bullet to be pushed into the case when hitting the feed ramp or under the action of recoil.