AER,
Below is a summary of my troubleshooting experience with the Bren semi auto. I used the striker design with the striker spring on the return rod. This was long before Mighty Lime's spring system.
I'm not sure this is the same system as Historic Arms. I think HA may have used a striker spring in place of the buffer and opened up the gas ports. If this is the case the striker is cocked on the rearward motion of the bolt. The system I used cocked the striker on the forward motion of the bolt.
I did find as CSMarcher noted removing coils from the striker spring sometimes made a difference.
Maybe this link will be of some help:
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Joe