Gotcha...It looks like the threads per square inch in that material isn't as tight as the pillow ticking I get from WalMart...

How about dry balling...
I'd patch a ball up, ram her down and then pull it back out...This will let you examine the patching before it's fired...Then you know for sure if it's being torn at loading or burned at firing...

btw...I'd also check the crown, sometimes that's where the tearing occurs...