Classic army have a handy lock system to avoid the frustration of the bearing balls.
Take the 203 base/shell
Install Firing Pin
Install Spring
Put the Firing Cap in place
Push the Firing Cap Down
From here, lightly tilt the firing cap to reveal each hole and pop a bearing ball in. Once you have gotten all in, push the firing cap all the way in, and click the firing pin. It should actually lock the little firing cap in the base, You can freely screw the top on.
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