Mec 650 Primer Seating Assembly 12 Ga.. If the primer is seated too deep below flush internal components can be damaged which causes inconsistent ignition and misfires. On the other hand seating too high which would be above the flush prevents rotation of cylinders in revolvers. For semiautomatics it can create problems when the bolt slams. Because this is so important only the best product should be purchased which is why reloaders depend on the MEC Primer Seat. Specifications for Mec 650 Primer Seating Assembly 12 Ga.: Manufacturer: MEC Fabric/Material: Steel Finish: Black & Silver Gauge: 12 Package Contents: Mec 650 Primer Seating Assembly 12 Ga. The Mec 650 Primer Seating Assembly 12 Ga. is a quality addition to the MEC lineup. For more great deals on Press Parts & Accessories by MEC please browse our Mec Reloading Equipment page. Mec 650 Primer Seating Assembly 12 Ga.