7.62mm Semi Bren. Failure to chamber

My semi auto Bren has a loading problem. The round is being stripped from the magazine but then ends up failing to chamber with round being 'stovepiped' between the bolt face and the barrel with the bullet facing down through the ejection port. Playing with snap-caps suggests that the round is not being held tightly enough on the bolt face and the front of the round is dropping down below the mouth of the barrel before the bolt closes. Could this be something as simple as a worn extractor stay spring?

Historic Arms?

Yes, indeed. Has been running fine up to now, but not used it for about 8 months now due to moving and not having access to a range

Are you using the same magazine that functioned previously?

Also Is this a Zb39 magazine set up or was your gun set up for the UK 7.62 mags?

It is the same magazine that was working before. There did seem to be a small ding along the edge of one of the feed lips which I straightened out and it didn't seem to make any difference. It is a 30 round L4A1 magazine

I doubt it has anything to do with the magazine or the extractor spring.

Wally has much more experience with Historic Arms, so I will wait to see what he has to say.

If you can get a Zb 39 magazine and see if it feeds... the fact that the feed lip was adjusted is the change that took place between function and malfunction. Not sure what modifications (if any) were made by Historic Arms to allow for use of the L4 mag in a .303 gun body... may not conform to the official conversion mods done by the UK military. The South African barrels usually function well with a .303 bolt and Zb mag... your variables should lie with the mag.

Thanks Wally. I think it was the magazine. I played around for ages this morning looking at what was going on. Rounds were even falling out of the mag and out of the bottom port when I pulled back the charger handle and held it to the rear. When the action went forward the rounds were being stripped but not seating properly in the hole on the bolt face. Anyway, I altered the feed lips a little at a time and it seems to consistently feed, chamber and eject all my snap-caps (a run of 8) when I quickly cycle the action now. I just need to try it at the range.
My magazine was loose when I moved house and must have been damaged somehow.