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Discussion Starter #1
COVID have given me the time to explore a few things I have wanted to do in the past.

This question is about a semi-auto Bren conversion. With multiple makes and ages of .303 and in the two semi-auto Brens I have, I get primer material flowing back into the rectangular firing pin hole. The headspace seems good in both guns. I do not get this with the same ammunition when fired in a P14 rifle. There are a number of online articles about this issue but no solution. Here's a post on another site.

I'm wondering if I could bush the firing pin hole, drill a round hole, and make a firing pin with a round end? Anyone try this?
 

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That is likely the material of the cap causing the flow. The original UK spec didn’t have that concern. The original design was a round pin but these would pop and pull the primers so a rectangular version was designed. If you can find a CZ .303 bolt I’ve a feeling they had round firing pins.
 

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mighty lime over at WG does that to all his Semi Bren Guns. You can do it. Are you using a stock firing pin or a home made job?
 

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I did mine 15k rounds ago. Welded the hole closed and redrilled it and made a round tip firing pin. Works good. The biggest hassle is getting the hole in the correct position. The firing pin hole is not parrallel to the bolt body.

As I pointed out in the thread you linked. At rest the firing pin should be flush with the bolt face not below.
 

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Discussion Starter #5 (Edited)
mighty lime over at WG does that to all his Semi Bren Guns. You can do it. Are you using a stock firing pin or a home made job?
Thanks for pointing that out. I have a lot of respect for mighty lime's engineering abilities as I use 2 of his tellascoping return spring and striker assemblies. It's the best arrangement around. My Brens are SA. I've used both new made firing pins (Len Savage and Kiwi) and stock. I have limited tooling so on the stock pins, I drill the rear of the FA pin and solder/pin a drill rod extension in the hole. It seems to work well.
 
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