I've noticed that on several of my .38 Special cases that they have small perforated-looking bands going all the way around the outsides of the cases. On some cases, these are ~40% of the way down from the mouth of the case, and on others, they are about 1/4" from the mouth of the case.
Coincidentally, I'm guessing this would be right about the area where a wadcutter would stop or a regular round...
The first cartridges were loaded with black powder. With BP the bullet rests against the powder, usually slightly compressing it. The bullet can't be accidentally forced deeper into the case increasing pressure. With smokeless the powder seldom rests on the powder so there is a chance that the bullet just might be forced deeper into the case. The cannalure makes a little ridge around the inside of the case that would resist the movement of the bullet farther into the case.
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I like to separate my cases by manufacturer and any major variation. I have fairly few 'ringed' cases, but when I did use 'em, I just treated them like the others - no problem!
Before you ask, some old black powder cartridges do appear to have a cannalure. This is actually a neck on the case. There are 'straightwalled chambered' guns with cases that have the very slightest of a neck, often when it's not needed, and some true necked cases. They tried a lot of different stuff in the old BP days.
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Aim real good we're nearly out of ammo.
Holy cow, Mike, you're a wealth of useful information. Thanks for the background on the cannelures. I almost used that word, but it just didn't make sense, given the context...now it does.
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Question about .38 cases 
