No primer strike

[84railsplitter]

Whats the Top three reasons the firing pin would not strike the primer?

Ejects unfired round by hand OK?

[woodsy]

The first thing I would look at is the firing pin (binding, too short, broken or missing).

The second thing would be the headspace. If it was too tight the bolt would not fully rise into the locking recess and the slide would not be able to go forward far enough to let the piston post strike the firing pin. This would still allow the bolt to cycle rounds through.

The third, and most unlikely reason would be a very weak return spring which had used all its energy before the piston post strikes the firing pin.

If your gun has a rewelded body then I would check that the piston slides freely throughout its entire stroke.

Please note that cycling live rounds through a Bren by hand is exceedingly dangerous.

[horsa (David Gordon)]

You might want to try another barrel for testing as well. If you or someone before you had been firing wartime ammunition which is corrosive and wasn't good at keeping the chamber clean, there could be erosion which is allowing the case to slip in just a bit too far or in some cases prevent it from seating all the way. Both would be related to headspace problems but could be resolved by another barrel if that is the problem.

I know the people in the USA that first produced the ATF approved semi-auto Bren guns found that only one in ten surplus barrels they tried would function reliably several years ago. So there really is a difference between $25 clean looking used surplus barrels and higher priced unissued barrels.

The British and Commonwealth had inspection cartridges as one method to check the chamber. They had a phosphate finish which would show problem spots as it is virtually impossible to detect with the naked eye looking down the bore. Erosion can also cause ruptured cases as the brass expands on firing and will bind into the tiny holes in the chamber. Makes it hang on from the inside and the bolt moving backwards after firing will tear the head off. Or if not enough pressure, will stay locked closed as the extractor is on the head and can't let go. This will only happen with live ammunition though and not with blanks.

Don't know your entire situation so some of this may or may not apply. Be safe.

[84railsplitter]

Thank you for your thoughtful advice

[nigelthomas]

You could also check the piston post to make sure that it is hitting the back of the firing pin when the breech block is in the locked position. De-activated Brens have the contact face ground away.