These were designed for the alarm made by PSomeone(their alarms and readme included in download) but they could be sanded down to fit any of these 12g type of alarms. 

'any primer holder'- the flat disc is for just your choice of primer

'any primer shell'- for those who may want to add something to the primer such as colored powder that would create a cloud of powder upon ignition, they can you can also fill them with whatever you wish, be creative, be smart, don't hurt anyone and also follow your local laws.

'12g any primer holder'- is made specific to fit in this particular perimeter alarm with just a detent for drilling. 

these are very simple prints that can hold primers of all size due to the hole not being present but instead a detent that can be drilled to your choice of primer(209, percussion cap, shotgun primer, etc..) 

Perimeter Alarm ANY Primer.stl

12ga_string_alarm_v2.STL

any primer shell.stl

flask funnel.stl

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Perimeter Alarm ANY Primer.stl

flask funnel.stl