Here's a question..........

[Peter Laidler]

Here's a simple question to kick-start the 2015 forum and hopefully get the brain cells working into the New Year for you Bren Fiends out there. And it's this. .303" Bren breech block....... Anyone out there know why the .303" Bren breech block has two distinct protruding feed horns at the top. Not required on any of the others including the 7.92 or the 7.62 guns.

Don't be shy in coming forwards because the person who's thinking outside the box will probably be on the right lines

Information

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[Woodsy]

There has to be two as the ejector has to fit between them, and they must be wide enough to pick up the rims from the staggered feed. Additionally, the forward projection allows the rims an unobstructed passage down the face of the bolt as they chamber. The underside of the projections also acts as a positive shoulder for the rim to sit against under the pressure of the extractor, holding the fired case in position to be struck by the ejector, giving reliable ejection.

[tankhunter]

Not quite right Woodsy. It needs two horns, because the rounds feed alternatively from either side of the Mag. The underside 'Projections' have no bearing as a positive shoulder. As the case sits firmly on it's base in a recess. It cannot move up or down in the recess. So therefore, as a positive shoulder as you call it. That is superfluous!...
Now, go back to your desk & try again young man! see Me after school!........LOL

good try though, well done buddy.

[Brit plumber]

It must be something to do with the rim on the case as the 8x56r ZB39 has similar horns.

[Woodsy]

Not quite right Woodsy. It needs two horns, because the rounds feed alternatively from either side of the Mag. The underside 'Projections' have no bearing as a positive shoulder. As the case sits firmly on it's base in a recess. It cannot move up or down in the recess. So therefore, as a positive shoulder as you call it. That is superfluous!...
Now, go back to your desk & try again young man! see Me after school!........LOL

good try though, well done buddy.

I did mention that the feed horns had to be far enough apart to strip the rounds from the staggered feed mag. I will now go and sit in the corner and have another think!

[Woodsy]

I have just examined 3 of my breech blocks and the underside of the feed horns are precision ground to the correct rim recess diameter, so the underside of the feed horns does provide a solid support for the rim against the spring pressure of the extractor. It has been my long experience with many firearms that positive ejection is very much reliant upon good positive case support during extraction.

I also suspect that the horns contact the rear face of the barrel in battery and provide a pivot point to assist the piston to cam the rear of the breech block up into the locking shoulder recess.

That is my 2 cents worth anyway!

[Peter Laidler]

I'll come in towards the end of the month chaps. Good and valid points all round of course.

The pivot point for locking up Woodsy are the breech block stops. When these are eventually worn down by the battering (usually by the dopey training staff using SERVICE/live guns instead of unserviceable DP) that is the most(?) common cause of ZF in Brens

[TactAdv]

I guess in my mind, Peter, my more obtuse question here is since I am in the midst of a .308/7.62mm conversion to my Daimler MkII using a stock L34 BBL......is there any issue in milling off the horns on a spare std .303 bolt to match the L34 BBL face??

(I know that the .303 bolt is not "ideal" with the other issues of the larger bolt face as-is, but I'm not addressing that YET, just the fit of the bolt-to-BBL face.)

-TomH

[Brian Dick]

You might try SARCO as they had some spare 7.92 Inglis bolts a while back. Get Dave on the phone and ask him.

My simple answer for the question was because it's a rimmed cartridge. OVERSIMPLE I admit. Looking forward to the details Captain Laidler Sir!

[Brit plumber]

The .303 bolt is shorter so if you are doing a true conversion then it won't work. Also, an L34 is a silenced Stirling so I assume you mean a L4 barrel?