Machining No4 receiver to take 7.62 mag

Hi guys, I'm rebuilding a No4 in 7.62, and have "that feed issue". Previously I've been able to get them running by tweaking the tabs on the mag, but I cant see this one obeying.
It needs to sit just about 1-2mm higher for the bolt to pickup the round on the right hand side of the stack.
I've got Peter Laidler's drawings of where to mill it out in a Skennerton book, but I'm not so flash on a mill and don't want to stuff it up.
I was hoping for some very specific advice on how to jig it up/set the receiver (and barrel) up on the mill properly to as much as possible avoid 1st timer dramas.
Thanks.

Its far easier to try a few standard No4 receivers and choose one that will feed from a 7.62mm Enfield mag without alteration.

The factory rifles were obviously converted on a jig that used a datum from the boltway; I imagine it would be quite hard to replicate this with any sort of precision, lacking the gauges and tool settings.

A good machinist with a milling machine can make the necessary cuts with ease using the drawing from Skennerton's book which was supplied by P.L. I've had a few done over the years and they're perfect.

If I remember correctly TBone and others, there's TWO ways that this can be done (but only one factory way of course). It's a case of raise the Titanic or lower the Atlantic.

The 7.62 Enfield magazine doesn't fit in a No4 because it rocks at two points. On the top left and right hand side of the magazine case and for an inch between the front and rear feed lips. So on SOME unmodified bodies, when the magazine is pushed up at the rear and clicks into place behind the magazine catch, what you have done is rocked it downwards at the front. This allows the top cartridge to sit perfectly into the bolt way and be pushed forwards but in doing so, it stubs the nose somewhere on its way into the chamber.

If you now disengage the mag from the mag catch and rock it upwards at the front, you'll find that the nose of the bullets swim up the feed ramp straight into the chamber.......................... They WOULD, but by allowing the mag to drop at the rear by disengaging it from the mag catch, the rim of the rounds is just below the correct pathway of the bolt face so you get a misfeed.

Both these situations are things are things that a sniper definately doesn't want. So you can machine the body recesses deeper or…………….

Appreciate that I am only going from memory now but a paper was circulated to Base workshops and Armourers handling L42’s about these problems in the early days. It wasn’t a project I was involved with, it was WO1 Frank S------. It was all because while the machining was done to a pattern, the fact remained that the bodies were all (?) slightly different so problems arose I can’t find the report so………….

The answer was to file these two sections of the magazine to a lower sidewall height. Usually just a couple of mm’s or 1/32 will suffice, JUST sufficient to prevent the magazine rocking about the axis point. Now, when the magazine is inserted, it will seat fully into the magazine well, tight at the front and click tightly in place at the rear. You might need to tweak the lips a gnats knacker (a well used REME technical term indicating ‘not a lot…….’. I hope that you’re all absorbing and taking on board these technical phrases as there’s an exam at the end……).

Now, this will answer a bit of a mystery that some of you might have noticed in the past…… SOME L42’s have their magazines numbered, while others don’t. And this is the reason. If the magazine has been altered to fit THAT rifle, then it must be numbered. After all, what sniper wants a misfeed…………?

During the later part of the Summer I’ll cut up a No4 to show in photographs exactly what I mean but you get my drift

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Hey, come on........... there MUST be more than 7 people appreciate this little gem! Where else would you get inside info like this? By pure coincidence, I spoke to ex WO2 Frank Squires today and mentioned this magazine querie to him. He chuckled and added '....... it wouldn't be so bad if it were the L42's only problem but the whole project was done on the cheap'. Just as I have mentioned several times in the past.

Thanks guys, where else in the world... I'll try the filing tonight.

Filed as instructed, and it seems better, but now the mag is able to be pushed up at the rear, ie. it is not being held right up by the catch. The mag will feed when pushed right up into the well but is hit and miss at the moment. I'll try a different catch, and failing that I'll solder a new spine bit on that engages the catch. I'm not set up to braize.

All good, extended the spine so the mag would seat higher in the well, as allowed by the relief of the side walls. Mag feeds, extracts and the rifle ejects. Thankyou Peter Laidler.