Sterling Mk5

[Vincent]

Attachment 65570Attachment 65571Attachment 65572Attachment 65573

It’s a tube gun with a modern sound suppressor that makes it extremely quiet. The finish is powder coat. There are a few things left to do, but I thought some of you would enjoy seeing it.

Information

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[browningautorifle]

Of course we do. You know I'm up for this...wondering how much the suppressor is varied from the original design, J baffles? K baffles? A far cry from the Archimedean screw... You should do a short vid when at the range next...? Both with subsonic 147s and with 115 ball. Just for yuks...

[Peter Laidler]

Is the breech block eccentrically machined internally too? We didn't like the wood hand grip for some reason. Probably cheapness. Is the barrel the standard un-drilled version. Interested to see how they improved on the silencing properties. I wish I had access to the MPL high speed video of the trials. VERY interesting design aspects were highlighted in it

[Vincent]

It has an M stack in it at the moment. I am going to replace them with an Omega stack or a monolithic if I can get the FRP down enough.

It doesn’t have the long rods but the layout is basically the same as the original, ported barrel, baffles and expansion chamber.

Is the breech block eccentrically machined internally too?

Attachment 65579

Yes, it is.

The blue heat mark is where the metal is very thin and couldn’t dissipate the heat from cutting very well. There would be a hole on the left side if was machined symmetrically. Patchett knew what he was doing when he offset the hole to the right.

Attachment 65580

The barrel is drilled. Real Mk5 barrels are not to be found here. I will fill a barrel with melted lead and drill the holes in rifling groves and melt the lead out when it gets cooler here.

[browningautorifle]

drill the holes in rifling groves

I know that's the theory and all...but I found it didn't make a whale of a difference...

Maybe it keeps the bullets from shaving a bit though.

[Peter Laidler]

Theres more to it than that though BAR. It's all to do with the mathematics of the gas loss, boyles law and all that stuff and integral strength that the drilled barrel retains.

The total area removed by the holes was just slightly more than was mathematically required to gradually bleed off just sufficient gas as the bullet was traveling up the bore so that the m/v would never quite reach the speed of sound. And don't forget that as it is traveling up the bore, initially, the propellant gas is still being produced and that has to be dissipated too.. It was calculated using NATO standard Mk2z ball ammo.

They were drilled radially because if they were drilled in a straight line, in say 4x rows, the distance between hole centres would be so close that it could/would affect the structural strength of the barrel. By following the rifling the holes are offset to each other and structural strength of the tube remains sufficient to withstand proof.

If you fire a 9mm UK Military proof round in a barrel with 4x linear lines of holes the barrels will stretch and bulge*. But not with the holes radially drilled

* I cannot confirm this as I am repeating what I was told and read in the trials stuff

Just been reading this again and it doesn't seem to read right!........... But it's getting late as well! Later I'll mention the brilliant design of the muzzle cap.

[browningautorifle]

I think all this is what I read before...encapsulated. I suppose the ones I've dealt with haven't undergone the rigors of military testing and will never see much use...don't know how I'd manage to do them in the grooves...?

[Vincent]

What’s available here at a reasonable price is off the shelf pistol FMJ’s, 115gr and 124gr. To get Mk2z performance you have to go to a +P and they are usually JHP’s that don’t always feed well in a Sterling. You can buy ball with Mk2z performance, but it’s very expensive. So the barrel in the picture is optimized for what’s available here at reasonable prices, pistol ammo that’s about 110 ft/s slower than Mk2z. Instead of 72 holes the barrel only has 69 holes.

The pistol ammo puts less strain on the barrel and when you’re dumping gas to keep the muzzle velocity down there’s no advantage from higher performance ammo. It just makes more gas that has to be vented to keep the bullet subsonic.

I don’t know how the barrel would take a squib load. I have had them with the Mk4 and they bulged the barrel, but the gun kept running.

Later I'll mention the brilliant design of the muzzle cap.

I am looking forward to reading that.

don't know how I'd manage to do them in the grooves...?

“Simple” or “Plain” indexing with a dividing head is one way.

[browningautorifle]

I'd still probably use 147 subsonic factory. Shouldn't break the bank for bulk buy.

[Vincent]

Can you recommend a brand of 147?

I have tried a few brands in pistols. They seemed to have a lot of blow back gas and need a booster to cycle reliably. I am not sure they would push the Sterling breech block back far enough.

Fiocchi and IMI 158gr seem to have less blow back gas and work without a booster. I wouldn’t think 11gr would make much of a difference. Maybe it’s the powder?



Attachment 65628

The back half screws onto the barrel just like a pistol suppressor. The front half screws onto the tube. It’s very light.