Bren MKII to L4 Gas Shield

[c310pilot]

So I have seen some pics of the gas shield cut and some unmodified. What is the proper mod for this area if any? On a side note. My gas shield is out of plum. Not sure how this is possible being it keys into the receiver. What should be my course of action?


IMG_8709 by c310pilot, on Flickr


IMG_8711 by c310pilot, on Flickr

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Peter Laidler]

It definately shouldn't be out of square as it is indeed located squarely in the body. If it IS out of square, then so will be the barrel lopcating lug AND you won't get the barrel into the body due to one of the upright ears of the gas blast shield obstructing it. Mind you, it looks to me as though the actual body is twisted........ And that is BAD news

OR, it could be that the gas cylinder part of your parts kit isn't welded in square. I suppose you COULD grind away the offending part of the upright ear of the gas blast shield providing that the gas nozzle on the barrel gas block still seats properly/squarely into the gas cylinder.

Anything else need answering? Fire away....... if you'll excuse the phrase!

[c310pilot]

I don't think the body is twisted as it fit on my jig nicely, but I will definitely do some double checking. So the ears are suppose to be intact?

[Kev G]

Looking at the first pic the (down the line) you can see the very last section of the body that holds the gas cylinder retaining pin is out of square/canted with the gas shield,notably the barrel key way.If the body was twisted these two items should still be in line ?

Pull the gas cylinder and remove the gas deflector to see whats going on with the location tangs.

The L4 gas deflector is not listed in the IPL but is MG 4971



ATB KG

[Brit plumber]

It looks like its just the locating part of the shield thats got distorted. If you zoom into the square locating bit, it looks twisted and I bet the other side will be twisted the other way.

You can see how feable these small square locating pegs are in this pic.

[Peter Laidler]

Got to respectfully disagree chaps......... Look at c310's first photo again. Looking forwards through the barrel opening where the gas cylinder end is cut off JUST in front of the barrel locating port. (we are looking from inside where the barrel locking lever is usually positioned). That barrel locating lug at the botton of the U shaped ears AND the ears ARE canted over to the right. THE UPRIGHT BARREL SUPPORTING EARS AND THE BARREL LOCATING STUD ARE BOTH PART OF THE GAS BLAST PLATE/SHIELD. This means either a) the female horizontal locating recess in the body is twisted or b) the corresponding projection in the gas blast plate is twisted.

This is absolutely nothing to do with the actual gas cylinrder per se as this is a simple sliding fit retained with the taper pin. The gas blast shield is located solely between the gas cylinder flange and the front face of the body and prevented from twisting by the very horizontal locating slot.

And don't forget c310 and others....... That from memory, the butt slide runners in the body end about 6" REARWARDS of the end of the body WITHOUT the gas blast plate and cas cylinder! So a body could be twisted from that point forwards and STILL slip nicely onto your jig/mandrill - and indeed a butt slide!

Just my 2c's worth - but I am always willing to learn about Bren guns of course........

[c310pilot]

Well I am going to try and disassemble the gas cylinder as I have nothing to loose. If the front section is twisted I will need to locate a donor portion. As far as the pin goes, do you have any tricks for getting the pin out? I shattered two pin punches in the press, shattered two drill bits, completely bent a nail set that I modifies in the lathe. Its not going well. Started to drill out, still no luck. Now I have a hole all the way through on center and the thing still wont budge. I am running out of options!

[c310pilot]

What size is the taper on the pin? I will probably have to purchase a taper pin reamer and get it out that way? Once the pin is out I don't think I will be able to get the gas tube off either. What a can of worms................

[Brit plumber]

b) the corresponding projection in the gas blast plate is twisted .

This is what both myself and Kev have said, its the locating bits on the gas shield which have distorted, when you zoom in on the pic you can see it twisted.

---------- Post added at 12:17 AM ---------- Previous post was at 12:15 AM ----------

Well I am going to try and disassemble the gas cylinder as I have nothing to loose. If the front section is twisted I will need to locate a donor portion. As far as the pin goes, do you have any tricks for getting the pin out? I shattered two pin punches in the press, shattered two drill bits, completely bent a nail set that I modifies in the lathe. Its not going well. Started to drill out, still no luck. Now I have a hole all the way through on center and the thing still wont budge. I am running out of options!

Not teaching you to suck eggs but did you press the pin the right way?

[Peter Laidler]

It is a morse taper (but some have said that it is a Harris taper - but that's pretty academic. Sufficient to say, it's tapered! And that said, any suitable taper reamer and new pin should suffice) To get them out we used a very short stubby tough steel flat ended punch with the other side of the body supported on a hydraulic press table - and bobs your uncle. NEVER had one fail. However, what DOES fail, is MNk1 and 3 guns where the threads are locked solid with years of crap and carbon. Brian at BDL can vouch for this of course but take good heart c310 - worn Mk2 cylinders could be removed by heating the body and twisting the cylinder out and forwards using an old bipod sleeve. (or unofficially, a steel bar through the gas vents!). They come away quite easily and are readily available if you know where to look

I see exactly what you're saying BP (thread 9 above) but the male and female locating slots/projection in the pics just don't LOOK distorted. And that's a whole lot of distortion to give that amount of tilt.

If I was doing this, I'd identify the direction of the taper - I think it's right to left looking forwards and from the top - so remove from LEFT to RIGHT but don't quote me. Now slowly taper ream in the direction of the taper and very soon you WILL break through the edge of the existing taper pin. At that point the pin will 'crush' and you'll be able to pop it out.

Go and have a coffee first, sit down, have a break, refresh yourself and start afresh. All the best.

But here's something else. Even if the front gas cylinder part of the body is slightly twisted during the welding assembly, it doesn't spell disaster by any means. Just take the gas blast plate off and slide a gas cylinder back in. Now insert the barrel into the barrel seating of the body (the seating at the rear of the barrel nut) If the nozzle of the gas block in the barrel aligns with the gas cylinder then all is well and the linear position of the gas cylinder is correct. If it does, then taper ream the hole while it is in this mechanically perfetly aligned position.

But what about the gas blast plate you ask........... Simple. You just get another or make another to suit the slightly misaligned geometry that you have.

Sorry to be a bit long winded but don't be defeated. It's just a case of 1st year apprentice bench fitting