Modified Ejection Opening Cover

[Peter Laidler]

Here’s a thing....... Someone asked me a good question the other day about fitting up his Bren. And it’s this....... He couldn’t get the ejection opening cover catch (the EOCC) to operate. In fact it wouldn’t even fit! What was the problem he asked? All the parts fit after a fashion, even if it means a bit of fine fitting – as was the norm for the era.

The problem here is that during the late 60’s or so, damage was being caused to the front of the ejection opening aperture of the butt slide. The ejection opening cover catch was not engaging correctly and being hardened, was virtually battering the engagement part of the butt slide to oblivion. Once it did so, the ejection opening cover could, would – AND DID – slide rearwards with the piston extension, retain the spent cases and jamb the gun up solid. But before it quite got to this point, the hard catch had knackered the expensive butt slide.

The problem was found to be that the 40 degree angle of the catch the cammed it into engagement with the small shoulder...... blah blah blah......

Anyway, to cut a long story short, the original design was crap and causing problems. As a result of this a new catch was designed where the cam angle was much shallower giving a longer and more gentle run-in, lift the catch and hold the slide forwards as it should. And this solved the problem for ever more.

The new catch is marked with a small letter ‘M’ – for modified but, alas, not all were so marked. It won’t cause you a problem as the pictures amply illustrate the old and new

But, there’s a catch – if you’ll excuse the pun! The shallower cam angle and longer run-in made the catch slightly longer forward of the axis pin. And it is THIS extra length of the catch that will foul the front end of the original ejection opening cover. So, to get the catch geometry right, you have to slightly lengthen the forward part of the catch slot in the ejection opening cover.

At the same time, the actual spring was changed too. Don’t ask me why or how but it was! Let’s just say that if I was asked to waffle my way through the modification to a class, I’d be saying something like ‘...... to ensure more positive retention and engagement’ On that basis, just re-use your original spring!

Now let’s have a look at the two catches side by side pictorially

Left/right side view of the ‘long nose’ EOCC showing the standard Mk2 type catch highlighted in red marker dye top left.

Attachment 65477
(Click PIC to Enlarge)


Poor close up illustrating the longer and shallower run-in of the upgraded EOCC

Attachment 65476
(Click PIC to Enlarge)

This modification was applicable to all .303” and L4 Brens in service except for DP guns (nope, I don’t understand why either.....) and the original catches declared obsolete. Good question and that's the answer if you encounter the problem or find one in your parts bin

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