Military surplus .303 ammunition question

[Longshaor]

I recently pulled the bullets from 50 rounds of WWII-vintage .303 British ammunition because the cases were clearly too badly deteriorated to be safe. They are from multiple manufacturers (including some Canadian rounds). All the bullets have a noticeable cannelure, most have vertical grooves in the cannelure. What I'd like to know is this, after pulling the bullets, there was a slightly sticky, black substance in the cannelure and extending above and below it. What is this stuff?

Thanks in advance!

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[CINDERS]

The vertical striations in the cannalure are part of the machine process to hold the lead core onto the jacket, as for the gunk I have no ideas.

[Parashooter]

The black gunk is called asphalt(um) - a traditional waterproof sealant and adhesive.

[browningautorifle]

The black can be easily removed by spraying the bullets with brake cleaner and running them back and forth in a towel to dry. I've done lots...

[Longshaor]

Thanks, everyone! I was wondering if it was some sort of waterproofing. I'm surprised it was still pliant after all these years, some of these rounds were manufactured in 1937!

As far as removal, I just attacked it with a brass-bristled brush after tumbling them for two hours.