L4A3 (308) completion help

[Brit plumber]

Depends on the 8mm you refer to. Is it a 7.92mm that are often called 8mm or a 8x56 which is from the Bulgarian ZB39?

[alterego]

Sorry 7.92 (i.e. 8mm Mauser)

Am I correct in understanding that the South African 7.62x51's used a 303 breech block?

[Peter Laidler]

I'm going to say, rather hesitantly, that the SA guns do use .303 breech blocks. The problem as I see it, relating to you is that the base rim diameter (the BRD) of the old .303" round is greater than the same of the 792/762 round. And that means that as the empty case is extracted and drawn from the chamber, it is becoming a looser fit in the chamber each mm or so that it is is withdrawn rearwards. With me so far.....? Now, being a mechanical thing, the case will naturally take the least line of resistance. It cannot move DOWNWARDS within the BRD recess because the extractor claw is holding onto it. But the spent case CAN move upwards. And in doing so, the rim can lift clear of the clutches of the very tight extractor claw. And guess what.......... If it CAN, then at some time in the future, just when you don';t want it to........., it WILL. That is a scientific principle known among Trials and Development engineers as MURPHYS LAW.

Another point about the SA gun conversion was that because the conversion process used the existing breech block, locking shoulders and breech-end configuration, it meant that they could not modify the guns to A2 - 4 spec. I am just repeating this last para because that's what I have been recently told by one of the Enfield engineers involved in the early L4A2 & 4 project. This makes perfect sense to my engineering bent but I don't have two guns to cut up and analyse on the bench! It was previously reported that............ Anyway, enough of this waffle

[browningautorifle]

I know we turned a 7.92 gun into a 7.62 gun...can't imagine using the big breechblock face for 7.62...

[Brit plumber]

The SA block was a .303 block with a bush in the recess to size it for 7.62

[TactAdv]

Gents, I've posted pretty extensively on using the Denel/SA 7.62mm BBLs to convert a standard .303 MkII......check the other topic posts as I've included a ton of pictures and commentary.

In a nutshell all you need to do to a FACTORY ORIGINAL machine gun is exchange into the .303 bolt a std 7.92/"8mm" extractor, then plug in the SA 7.62mm BBL, and then use UNMODIFIED ZB39(8x56R) magazines.

It runs FLAWLESSLY using any .308 fodder I've tried. That's fullauto.

The whole reason this works is that Denel extended the rear BBL shank an equivalent distance as the difference in std "8mm" bolts. They are only intended to be used with UNMODIFIED .303 bolts.

Contact me privately for any questions.
-TomH

[ActionYobbo]

in the past I had 3 SA bolts and 1 barrel. the bolts were standard 303 but a 303 rim would not fit under the extractor so there was a difference there.

[Brit plumber]

I could have sworn a bush was fitted to the SA BB but there is no reference to it in the text below (This is taken from a SA forum).

2. Breech Block: - The existing Breech Block was modified to accommodate the rimless 7.62mm Cartridge by having the vertical face of the Block machined away, reducing the depth of the cartridge pocket within the Breech Face. The existing Firing Pin assembly was retained and the protrusion of the Pin corrected by hand to suit the 7.62mm cartridge. The Ejector Claw was changed to a new made unit specifically designed to accommodate the rimless round, retaining the standard spring and guide assembly. This Claw will be found to be marked: '7.62' by hand with electric pencil.

[Kev G]

Not sure if the thread is on getting a 303 to fire 7.62 NATO by any means or the SA conversion of 303 Brens to 7.62 ?

The observations below relate to SA converted Brens.
The south Africans kept to the British BE/BH part No prefix on unmodified and modified parts. Modified parts were marked With an 'M' such as the breech block and rear sight cam (on MKI's) New made parts had a TSC part number prefix such as extractor (TSC 707/1)

The breech block has the feed horns machined off the front face along with a skim to allow for the thinner cartridge base rim.The ramp of the feed horns has also been machined parallel on the top.

Attachment 83892

The SA extractor once engaged pulls the cartridge rim off centre to the top of the pocket in the breech block and holds it tight with no play.

Attachment 83893

As Mr E has said a 303 rim base will not engage with a SA 7.62 extractor.

ATB KG