Well chaps, I did ask and you said yes, so here goes. This isn't a technical article as such, just describing the pitfalls and suchlike. It would be very easy to go beyond the point of no return if you were doing the real McCoy so this is aimed at converting a deact/dewat. Here goes........, and thanks to the several unamed who helped along the way.
A very timely question was raised by a former a week or so ago regarding the conversion of a .303” Bren to L4A2 on spec. I have been on just such a quest for the past what seems like an eternity weeks or so! And I know that another
UK
forumer has done/tried/attempted/partially failed something similar in the past so I hope he will chip in too…….
The very first thing I’d have to say is, well……., don’t bother yourself! It is excruciatingly difficult, even with a reasonably well equipped machine shop. And I didn’t want anything that was a rock and roller or even a - shooter, just a good to the point of externally indistinguishable repro. To be honest, I had most of the engineering drawings and had seen/remembered more about these L4’s than I care to think about. To be honest, the drawings seem to relate to something different and the machining doesn’t relate to the inserts and the inserts……….. And on and on it goes. To be honest and frank I do not believe anyone who states that he HAS successfully converted a .303” Bren to a live fire 7.62mm L4 Bren. I would clarify this by lowering the standard to say that not only a live-fire L4, but one that will function with drill rounds and conform to the basic gauge specs too. Anyone prepared to accept the challenge?
How Enfield ever fitted the new spaced ejector block/magazine catch with the drawings they were supposed to be working with is just beyond me. My only saving grace was that I was intimately involved with the fundamentals of both the Bren I was using and the L4 that I hope to achieve. Or as one wag suggested, were the drawings so ambiguous that they’d effectively prevent another nation from doing this and keeping the work in-house might be the very reason for the difficulties in deciphering them!
The problems start with deciding WHAT you’re going to start with. If you are in the UK and starting with a standard UK spec dewat/deact then the very first problem is stripping it down carefully. I won’t go into the niceties of it but it came apart and the almost immediate further machining quickly meant that it was now even FURTHER deactivated to the point of even MORE totally inert than when I started! I would venture to suggest that the internal machining you are about to undertake to the body is so severe that any notion that you are effectively making or converting it into something fireable or useable is ridiculous and would not need re-certifying. Just my opinion based upon my experience. If you start with a bog standard but expensive Mk3 gun then the problems are just about to start. You’ve got to get yourself a ‘new’ barrel and that could be a BIG hurdle/headache. Because in short, the Mk3 gun barrel is too short and light to convert to the later A2,3,4,5 gun spec so you have to start with a Mk2 barrel and set about machining that down to a) length and b) diameters. I stripped mine completely and the gas block came off quite easily. Then when it’s all machined, align EXACTLY square the new pronged flash eliminator. These seem easy to acquire.
To be honest, the steel quality of the barrels ensures that it cuts like a dream. If you are starting with a Mk2 barrel, here’s the basic dimensions for the two later type barrels as fitted to the A2 to A5 guns. Main rear diameter up to the carrying handle should remain the same as it is. The second and third sections, up to the and past the locating section (that seats just to the rear of the blast shield) should be machined down to .910 and the diameter from the gas block forward is to remain the same, at .870” or thereabouts. This section must be reduced in length to give a barrel length from the gas block forward of 5.4”. The total barrel length of the L4 barrels being 21” or 24” including the fluted flash eliminator that is sleeved over the muzzle section. If you are doing an L4A1, then the diameters are as for the Mk3 gun barrel but the length is 24” overall, as the A2 gun barrel. Don’t forget to machine the flash eliminator to suit too!
I decided to use a Mk2 gun so the first thing was it had to be converted to Mk2/1 spec with the ‘hump’ used to stop the cocking handle from reciprocating being machined off and the new block to accommodate the old Mk1 type folding cocking handle brazed and pinned in place. This is not the case with ALL L4A3’s and 5’s and the A5 Navy BR parts list clearly identifies both cocking handles as ‘A/R’ indicating ‘as required’. I chose to. I started to follow the drawings for the new ejector block but these drawings were clearly done by a fluent Swahili writer….., somewhere! Eventually I just followed my nose and milled carefully until the new ejector block fitted well and could be locked in by the pin. This ejector retaining pin is an important datum
Likewise with the front of the magazine well. The drawings were not a lot of help. This time I can only presume, because they were formulated to use while the body was canted at suitable cutting angles. So I did it by eye by doing this…… I took an old L1A1 rifle magazine and un-brazed the front locating lug (you could use an old alloy FN rifle magazine and dolly the small knib flat….). Then carefully machined the edges of the magazine well parallel from about half way along the opening, forwards. Then forwards and down into the front face of the well so the magazine would lock at the rear, sit square to the horizontal body and JUST clear the remains of the body feed lips. To do this, you’ll need to mill out the magazine well to the depth of the slave magazine that you’re using. That means totally removing the old .303” Bren magazine lip supports. Lastly by careful calculation I machined away the undercut for the magazine front locating lug.
Inserted ‘stop/support’ pin for the body locking nut plunger spring after cutting 3 coils off the spring. I couldn’t even start to decipher the drawings to locate the two body inserts so accurately positioned them from drawings taken from an L4A4 gun!
The next thing you’ll find is that when the magazine is fitted, the old .303” breech block will not rise fully to lock-up behind the locking shoulder. This is due to the fact that the new geometry of the deeper seated magazine due to…… and…….. and….. The answer is to convert the breech block to 7.62mm spec by grinding the top outer surfaces, the surfaces astride the feed horns (and grind them off parallel with the front face of the block while you’re there too…….) so that they are clear of the new 7.62mm rifle or Bren magazine lips and allow the breech block/piston extension and post to reciprocate freely without interference from the new magazine lips
If you want to go ballistic you could (I did, just to show willing) convert the carrying handle sleeve 21 hole Mk3 variety specified for the L4 guns (although we didn’t worry too much about these trivial niceties in the real world I have to admit!) and fit a Mk2 type parallel carrying handle
Next is the fitting of the Mk3 lightweight butt slide and butt assembly……… Haven’t got them? Well you can easily convert the butt slide but suggest that you scan the internet or elsewhere for the butt, butt plate and fittings. The butt plate……, yes……. And don’t forget that this must be modified to incorporate a sling loop at the top. And if we’re getting pedantic, don’t forget that the L4’s were modified in service with a ‘double sear’ across the piston post. L4/all Mk3 bipod sleeve with a gas shroud is a direct fit.
Bar out all old and engrave bodyside with new designation and add new UE type number
Would I do it again – or even bother……. An emphatic NO! But does it look good. Yes!
This is what you’re going to need. Mk2 or 3 gun
L4 bipod sleeve blast shroud or use an L4 bipod sleeve assembly
Modified Mk3 butt plate (easy to do)
L4A2 magazine catch assembly
Machine piston extension and piston post to ‘safe’ spec
Originally Posted by 
PM
