Decapping

[Dumpstick]

The brass that is prone to sticking primers is the brass that was wet with the primer in place, and allowed to dry.
Outdoor range brass is prone to this, as is brass that was wet cleaned with the primer intact.

Some sort of corrosion. One would think that like metals (brass case, brass primer) would be immune to galvanic corrosion, but it must have something to do with the alloy.
I know brass is a zinc/copper alloy, perhaps it has to do with the percentage of zinc.

 

[Oklahomabassin]

Good information Swampratt. I bet you are correct.

 

[Shadowrider]

This is why you decap before wet tumbling. I've had that happen maybe 3 times total and it was probably from range pickup brass that had been wet.

 

[Broncos]

Pretty rare Haven’t seen this in 40 years of loading I always punch primers before tumbling I use a 550b Dillon press

 

[rickm]

Some years back i had a few 38 spl cases do that to me, i just took a pick and pocket knife and kept working at it and got it out and went about the regular process of reloading it.