Lee Shaver 22lr adapter - case failure

I put a Lee Shaver 22lr in my 1885 Trapdoor. Took it to thr range today. Got about 20 shots off then this happened-
Attachment 283677

The case just peeled back. No squib in the barrel.

At this point im thinking it was a over pressure round. The headspace seems good. The window in the case is in the area of the adapter that holds the head of the case. This is the only unsupportted part of the case. This is about the same amount as a barrel has cut out for an extractor.

Attachment 283678

Have you asked Lee Shaver about it?

No. I really dont think it was a problem with his adapter

He might benefit from your experience though.

This was Remington Golden 22. Its a high velocity 22 round. I have a bunch of these and no real use for them.

I think im going to try standard velocity.