Always wondered why some 38 Special cases have one or more cannelures while others from the same manufacturer have none?

What purpose do they serve? They must be there for a reason, it must cost the factory extra to make them.

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-jwk-
US Army '72-'95

Good morning
As I understand it that little cannelure is so the bullet should not be able to enter the case any further causing excessive pressure at ignition. Military and some police departments required this on cases so an individual would not have to be concerned during reloading in very dark situations. Simply dropping a loaded round from 2 feet can reseat a bullet rather deeply into a non cannurled case. Some thin walled 38 speacials cannnot take much addition pressure. Even 1911s can be ruined by shooting SHORT loaded rounds.

Interesting. I have seen the cannelures on lots of my 38/357 brass and always thought they were from when the round was made and crimped. Then wondered why they did not "iron" out when I re-sized the brass.

The brass is actually made with those cannelures in them?

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Still Running Against the Wind

There are two reasons for cannelures. One is to hold the bullet in place, especially when the cannelure on the case corresponds to one on the bullet. As previously mentioned, pressures go up when the bullet is pushed back into the case. The combination of lightweight revolvers and heavy bullets could due the opposite; recoil pushes the bullet forward, sometimes preventing cylinder rotation. Charter Arms Bulldog 44 Spls, as an example, were very prone to this.
The other reason is to differentiate loads. As an example, Remington 38 Spl JHPs in 110, 125 and 158 grain have different cannelure placement.

Bob Hart #946

I like to think of it as the case being pulled off the bullet, rather than the bullet being pushed out of the case. The bullet tends to want to remain still.

In revolver ammo, the case & powder charge does pull back from the bullet and this can lock up the revolver. In an autoloader, the bullet slamming into the feed ramp has a tendency to push back into the case, raising chamber pressures.

Bruce

These cannelures seem to be far below the bullet and very slight. Load identification seems to be the best idea I've heard,

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-jwk-
US Army '72-'95

Howdy

Modern cannelures on brass are too shallow be useful in keeping bullets from moving. Frankly, I just think they are there for decoration, or perhaps to identify different loads. They would not do squat to prevent a bullet from telescoping into a case.

These cannelures on some old 38-40 ammo are a different story. That one on the right would definitely prevent a bullet from moving down into the case. Modern brass does not have cannelures like that.

Attached Images

USCCo38-40.jpg (35.3 KB, 956 views)

Uh dude, the bullets are of different length and the cannelure is at the base of the bullet. THAT'S why the cannelure is in a different place.

The cannelure actually doesn't have to be too deep to provide a ledge that keeps the bullet in place during feeding/handling. The .38-40s pictured were used in weapons with tube type magazines, and the manufacturing capabilities aren't what they are today, so there was more effort put into making sure the bullet didn't back into the case.