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

[TactAdv]

Hi Peter!,
....well, THANKS, that would be fantastic if I could get the measurements to use!! And, I'd just be re-using the Mk II FH, so no problem there.

On the provided picture.....doesn't that barrel for sale there @ APEX, show that the front end is already profiled and notched for a FH??? What am I missing....??

Of course, the real answer I suppose is to get in the car and just drive down to APEX and pick one up and look.....not that far away from here...

-TomH

[Brit plumber]

It is machined for a FH but it isn't machined for the locating pin. If I remember correctly, Peter has said previously that this pin slot was made when the FH was assembled to the barrel.

[Peter Laidler]

How to machine and modify a Mk2 barrel into a look-a-like Mk4 barrel.

The barrel you are going to make from your machined down Mk2 barrel is the BARREL assembly Mk5. There is a degree of, er….. disagreement about this designation because depending on whether you believe the drawings OR reports of the time, the Mk3 barrel was either the bare lightened Mk2 BARREL or, as some wartime era Armourers have independently stated that so far as their teaching was concerned, the Mk3 barrel was a Shepherd (yes, that’s him of Sten fame) formulated, hammered Accles and Pollock barrel with the possibility of it being a ‘2 groover’ too. The recently unearthed engineering drawings now show that the barrel descriptions shown above are correct. Where does that leave the missing Barrel, assembly, Mk4 then? Simple! The Mk4 barrel was a new production barrel for the Mk3 gun.

But don’t worry, the principal difference between what you are going to make (a Mk 5) and the Mk4 barrel is the slightly different gas block and flash eliminator. Oh yes…..,., and the carrying handle sleeve which you can modify as the mood takes you!

That’s the history lesson. Here are the measurements you’ll need. The barrel is split into 4 sections. Remove the flash eliminator. Removing the taper pin from below. The flash eliminators are not particularly tight and will knock-off using a rawhide or plastic mallet.

1) The rear, from the narrower breech section forwards to the carrying handle sleeve area. This should be taken down to .960” diameter, rounded at the ends down to that diameter

2) The mid-REAR section, from the front end of the carrying handle sleeve area to the rear of the front barrel support. This area should be machined down to .900” and rounded at the ends

3) The mid-FORWARD section. From forward of the front barrel support to the rear of the gas block. This section should be machined down to a thickness of .900”. But this section is a tad more difficult as this machining extends under the ‘nozzle’ of the gas block. You can either press the gas block off and on again making sure you align the gas port and taper pin OR with the muzzle end in the chuck, simply machine under the rotating gas block nozzle.

4) The FRONT section is to remain as it is, that is .875” diameter.

Can I suggest now that BEFORE you start to reduce the length of the barrel, you mount the muzzle in the lathe and using the existing flash eliminator locating lug recesses, accurately follow these rearwards using a sharp lathe tool so that the exact positions are carried rearwards for use later.. Continue machining this smaller flash eliminator diameter rearwards until the new shoulder is exactly 2.45” to 2.5” FORWARD of the front face of the gas block. Now machine/cut off the barrel 1.5” from the new flash eliminator shoulder. Drill and ream, replace the taper pin

It’s as simple as that! For the most pedantic of you, these measurements have been taken from 5 Mk4 barrels and differ by as much as .012” on some. So it’s all been rounded out.

The barrel you will have now will be slightly shorter than the overall length of the Mk4 barrel because the Mk1 flash eliminator you have used is slightly shorter than the Mk2 flash eliminator used on the Mk4 barrel…. Don’t worry about it. There it is, a xxxxxxg good replica of the lightweight barrel used on a Mk3 gun.

Did someone ask about the differences between the gas blocks? The Mk4 barrel gas block is slightly narrower and therefore lighter. And the carrying handle sleeve…… If you want to convert that to the lightweight Mk4 barrel type, just mark out and drill the 7 lines of 3x holes, exactly as per the Mk1 carrying handle sleeve. All you need to do now is to bead blast, phosphate and paint. Just make sure that it's heat resisting!

[TactAdv]

Thanks, Peter!! On the winter project schedule......

-TomH

[theczechboss]

thanks peter i couldnt find it earlier , so has anyone tired one of these yet , in all said and done i need to buy a couple i want one for my mark 2 and on for my 7.62x39 gun