Any chance of a bad crimp and your bullet partially came out of the brass, or an undersized bullet. Either could cause powder to burn slow (more of a sizzle) and velocity to be way slow.
After looking into many cases one at a time your eyes can get tired and assume you have seen a case at the proper fill level
when in fact you did not.
This can and will happen.. a loading block could be your friend .. as you look into a bunch of cases at a time and scan them and the odd one out(too high or too low) really pops out..
If you PM me your address I will send you a free Oak loading block for the size you load for.
As this may eliminate, I say may eliminate the issue.
The rest is up to you.
Swell guy!
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