What might cause this?

[12DMAX]

Hard to see in picture, I'm getting a lead ring on the outside of case neck just below the mouth. Cases not sealing in chamber?

Load:

31141 @ .310

27 gr 3031

seated gently against lands.

[462]

Had that happen when I didn't expand the case mouth enough. Some lead was shaved off and the seating die compressed it onto the case.

[I'll Make Mine]

If that's happening (or visible) only after firing the round, you're seating the boolit deeper as/after your crimp is made, and the crimp is biting into the lead. Back off your seating die a quarter or half turn and the crimp will ride into the crimp groove (assuming there is one) rather than cutting its way out of the groove. This could also happen if the boolit pushes back into the case on chambering, in which case you need to seat it a hair deeper, or have more neck tension so the rifling starts to engrave rather than just pushing the boolit back into the neck.

[12DMAX]

If that's happening (or visible) only after firing the round, you're seating the boolit deeper as/after your crimp is made, and the crimp is biting into the lead. Back off your seating die a quarter or half turn and the crimp will ride into the crimp groove (assuming there is one) rather than cutting its way out of the groove. This could also happen if the boolit pushes back into the case on chambering, in which case you need to seat it a hair deeper, or have more neck tension so the rifling starts to engrave rather than just pushing the boolit back into the neck.

It's only there after firing, I will back off seating die a tad. I am seating right up tight to the front of the crimp groove.

[OnHoPr]

I am not sure of this condition, but just for pondering does it happen after chambering and then extraction without firing. More pondering, an excessively chamfer or possibly thick neck brass with a full neck resize and larger diameter boolit?

[12DMAX]

I am not sure of this condition, but just for pondering does it happen after chambering and then extraction without firing. More pondering, an excessively chamfer or possibly thick neck brass with a full neck resize and larger diameter boolit?

I do believe MAKE MINE found the culprit, I went and reset my seating die so I definetly was rolling my crimp into the groove with no chance of it biting into the ogive, shot a bunch and no more issues. Thanks for all your help everyone.

[I'll Make Mine]

Glad it's behaving better for you. :)