Having had the striker pin smear like most of you, I was trying to think why.
How does the striker pin cause the smear?
The obvious answer is that it is sticking out when the case starts moving.
When does the case start moving?
It starts moving when the case impacts the ejector.
If the striker is loose in the channel, how does it have enough pressure on it to cause the smear?
At the point where the case strikes the ejector, the nub on the striker is close to or impacting the sear nub for cocking. This is enough force to cause the smear as the case rotates from under the extractor hook.
How does the striker pin cause the smear?
The obvious answer is that it is sticking out when the case starts moving.
When does the case start moving?
It starts moving when the case impacts the ejector.
If the striker is loose in the channel, how does it have enough pressure on it to cause the smear?
At the point where the case strikes the ejector, the nub on the striker is close to or impacting the sear nub for cocking. This is enough force to cause the smear as the case rotates from under the extractor hook.