What is special about this "Gauged" Mk4 barrel???

[TactAdv]

Bren MK4 Lightened Barrel, Selected as Gauge W/No : Rifle Barrels at GunBroker.com



Why is this barrel marked as a "Gauge"??? Were they ever mean to be assembled and fired? CAN they be fired??

What areas on the barrel (tube) were meant to used to measure/act as a "Gauge"??

-TomH

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]

They were definately NOT to be fired!!!!! The Gauge barrel was really a specially selected barrel. made to the exact outside tolerance or if you were an engine buolder 'blueprinted' It served the same purpose as the bolt gauge on the rifle. In short, the gauge barrel was used to ascertain whether it was a barrel that was faulty or the gun body. Usually it was used to test for wear on the barrel seating, just to the rear of the barrel locking nut. It was also used to test whether the breech block stops were worn too.

THey didn't have a flash eliminator nor a gas hole in the gas block.

Ours were left in bright metal as I recall and the muzzle end was painted yellow just so it was easily identified. Guns with a worn barrel seating wouldn't allow the/any barrel to tighten up, even on the largest size barrel nut. At Base workshop the barrel seating could be bored out and a new sleeve pressed into place and machined to suit. You can often see the new sleeve insert on L4A3 and 5 - ex Mk2 bodies

[Kev G]

The few I have seen an examined have had the gas hole in the block as I pressume this opperation would have been done before the gas block was fitted and the barrels were gauged when 'hand selected'



No flash hider or machining for the flash hider retaining pin.

ATB Kevin

[Peter Laidler]

You're dead right KG, been told by a friend who has a collection of all/most of the gauges they did have gas holes but no flash eliminator. The Bren barrel was still used to test the 7.62mm guns too.

[Peter Laidler]

Just thought I'd hack this thread because a Mk4 barrel fits onto a Mk3 Bren and is also the gauge used on the L4 types which also use the Mk2 backsight......... Well, got there in the end.......

Was chattering to a group of old time Armourers on Friday lunchtime, as you do, and the subject of Brens turned up - as did the question of the gauge, Inspectors, barrel. But so did another problem. The Mk2 leaf backsight. Many of the Mk2,3 and L4's used to come in from units without resident Armourers under the heading 'DEFECTIVE BARREL. Inability to zero gun'. Inevitably the barrels would be viewed, gauged and tested for tightness on the guns and found to be perfect. After that, the fault was inevitably the backsight, or rather, the cursor slide.

What used to happen is the the cack handed clowns at these small minor units would allow the guns to slip and slide around on the floor of the vehicles and the cursor slide aperture protruding out to the left would bend. This was simple if it bent slightly forwards or back as being fairly pliable, you could easily dolly it back straight. But if the aperture part was bend down or up, that was a different matter as it had the effect of lowering or raising the backsight by several hundred yards (or metres) and that wasn't much fun. In fact it would/could easily take the gun out of the zeroable range of foresight blades. Furthermore, to repair this was more difficult and really needed a blowlamp! Even worse, it meant stripping the backsight down too!

As a simple test there was a method created by the Inspectors and examiners. And better still, it could be tested on the gun with the finnicky sight assembled! And it's this.......... To test whether a backsight slide aperture is correct in relation to the figures on the backsight slide, put a simple straight-edge or steel rule across the top edge of the sliding cursor and extending ouit OVER the protruding aperture part. The ring/circular part of the aperture part must be below the level of the rule by about .025", 'give or take a bit'*. If it is, then all is well with the backsight slide.
* 'give or take a bit'. = REME technical term for 'sort of....' or 'near enough....' or 'that'll do...' But you get the gist of it

All we need now is for the photo genius of Kev G to put into pictures what I'm waffling on about!

[raexcct2]

They were definately NOT to be fired!!!!! The Gauge barrel was really a specially selected barrel. made to the exact outside tolerance or if you were an engine buolder 'blueprinted' It served the same purpose as the bolt gauge on the rifle. In short, the gauge barrel was used to ascertain whether it was a barrel that was faulty or the gun body. Usually it was used to test for wear on the barrel seating, just to the rear of the barrel locking nut. It was also used to test whether the breech block stops were worn too.

THey didn't have a flash eliminator nor a gas hole in the gas block.

Ours were left in bright metal as I recall and the muzzle end was painted yellow just so it was easily identified. Guns with a worn barrel seating wouldn't allow the/any barrel to tighten up, even on the largest size barrel nut. At Base workshop the barrel seating could be bored out and a new sleeve pressed into place and machined to suit. You can often see the new sleeve insert on L4A3 and 5 - ex Mk2 bodies

Could this barrel be made to be fired with the addition of the gas block hole and machining for the flash suppressor or is there another reason why this barrel is unsafe to be fired?

[Peter Laidler]

I suppose you could do anything! But it wasn't proofed so in the great scheme of things, you couldn't be sure what you'd got. The question is this. Why the need to ask? If it's because you have some and need a lightweight barrel for your Mk3 gun, theres a simple answer........ Just machine a readily available/plentiful Mk2 barrel down because that's all a Mk4 barrel was in effect! That way you know it's already been certified for service as a live barrel and all that stuff. Just my 2c's worth

[raexcct2]

I suppose you could do anything! But it wasn't proofed so in the great scheme of things, you couldn't be sure what you'd got. The question is this. Why the need to ask? If it's because you have some and need a lightweight barrel for your Mk3 gun, theres a simple answer........ Just machine a readily available/plentiful Mk2 barrel down because that's all a Mk4 barrel was in effect! That way you know it's already been certified for service as a live barrel and all that stuff. Just my 2c's worth

I was just trying to see if this barrel could be used as the supply of NOS Bren barrels are drying up if they haven't already here in the US and no more barrels are approved for importation. I only have 2 Bren MKII parts kits and a demilled 8mm Bren receiver so I was looking at getting this barrel rebored to 8mm.

[TactAdv]

I'd point out that per my original post on this, these particular "Mk IV" barrels are indeed cut of the FH. See the picture.....
Attachment 56463

And, Peter, reason for interest is that there are, essentially. no other Mk IV barrels available here. While your idea of simply profiling an existing Mk II barrel is of course correct, not everyone here has access to a good lathe for one, and for two.........would you kindly have access to the actual dimensioned original drawings for said MK IV barrel....for those of us that DO have the machining capability?? ;-) ;-)

Making up a few "new" Mk IV Barrels from Mk II's sounds like another nice winter project....
-TomH

[Peter Laidler]

I will dimension a Mk4 barrel up during the next few days. There is a VERY slight difference between the Mk2 gun and Mk3 gun flash eliminators which I have explained in detail earlier somewhere. But unless you were xxxxxxg good/observant, you'd never tell!

Wait out!

PS. Tom, what do you mean in your tip line, thread 9 that '.....are already cut of the FH. See the picture' I'm looking at the picture you posted and ...., what.......