Sten mkII to mkV conversion project

[dadio]

This has been on the books for over 6 months and has been held up numerous times by obtaining parts (rocking horse manure and hens teeth from around the globe ,thankfully not my job).The basic idea is to take a pair of AGM mkII Sten and convert them to a mkV's using as many genuine parts as possible ,aiming to get as much genuine functionality as possible ,build is to be at the highest quality possible , one of my favorite customers who shares my vision has commissioned one and the second for a friend of his .
This might seem a simple enough job as most of the gun is already there but there are design challenges .
1 the stock must be removable like the original and contain the battery
2 the trigger housing must be extensively modified or fabricated from scratch ,not 100% sure yet
3 front barrel shroud needs replacing with smaller diameter one to mate with the re production front grip
4 bayonet mounting lugs need welding to the barrel
I started with the stock mounting ,now on the AGM the stock is locked in place by an Allen bolt , the genuine one is secured by a sprung button that is part of the end cap for the main spring , the bolt hole has been bored out to the right size on the lath for the button to pass through .The button is at the end of a deep cup shaped piece that fits into the main tube , now this tube on a real Sten contains the main spring but for us there's a gearbox and motor in the way , this means the cup must have a section cut out to fit round the motor , its going to be sprung as it should but by a slightly narrower than genuine spring that goes above the motor to butt against the back of the gearbox.
having got that far and while waiting for a spring i started another job ,separating the front from the rear of the trigger housing ,the front will be re modeled and a new longer real fabricated from scratch.







It's funny, when i started making these projects it was agony cutting up parts of the downer gun but i hardly think about it these days.

[dadio]

Re: Sten mkII to mkV conversion project

revised stock mounting system , new design uses the original end cap that has the half twist bayonet fitting , the horizontal bar on the original mounting is now completely removed ,its replaced by a sleeve that fits into the rear main tube and has the "L" shaped cut outs for the twist lock cap that retains the spring and stock locking cap,this sleeve will be welded onto the main tube , this means the rear sight barrel band part won't be under spring tension and as its only held on by one 3 mm screw its for the best .

[dadio]

Re: Sten mkII to mkV conversion project

Spring and barrel shroud tubing arrived so i temporarily fitted the rear baronet fitting for the stock catch and put it together , there's a really nice feel to the locking button , i need to weld on a return lip on the back of the barrel band/sight assembly as the AGM has none .
Also cut and terned down the front barrel shroud tubing and the alloy hop mounting piece to fit , now i just need to work out how many rows of holes to drill in the shrouds ,it seems to vary depending on what picture you look at , some had three rows ,some four and some seem to have 5 rows so i'll have to peer at a lot of photo's of mkv's and pick the most common number unless Chris had a number in mind ?

[dadio]

Re: Sten mkII to mkV conversion project

After a lot of looking at mkv pictures (such a chore ) I'm leaning toward 5 rows of holes in the barrel shroud's ,It seems most common followed by 3 rows ,I can't find any with the 4 rows that AGM went with but hey don't let being wrong stop you .

[dadio]

Re: Sten mkII to mkV conversion project

holes drilled ,sounds a small thing but marking them out before drilling takes a little time and precision ,you also have to drill them to 7.5mm then use a mill cutter of 8mm one each hole otherwise when drilling into tube the drill bit tends to give a semi triangular off round hole and the mill cutters don't suffer this effect but you cant really drill with them either so its a longer process than it sounds.

[dadio]

Re: Sten mkII to mkV conversion project

Got a bit more done , the twist lock sleeves are now welded into the main receiver tube at the rear .I also received some micro and mini deans to play with , what i have planned for then is to have them mate as the stock is locked in place ,that way there wont be an ugly umbilical cord of wires and plugs when the stock is removed , at least one of the owners does reenactment and may on occasion have the stock of in public so it can't be ugly .After ordering the plugs i found that micro deans are only good for 5 to 10 amps so not up to it but the mini deans are good for 15 amps and as these are not going to be walk on day hyper guns that should be OK .
A section of 35 mm steel round bar arrived as well last week so the barrel shrouds now have their internal mountings made , they screw into the the front of the receiver as the original barrel did with a 17 mm fine pitch thread and new barrels once made will screw into the shroud with a 14 mm left hand thread .The inside threaded section is at present an interference fit or in layman's terms its pressed in with a hydraulic press ,i may decide later on to weld them as well if they show any sign of moving .

[dadio]

Re: Sten mkII to mkV conversion project

New barrels made , i might take the narrow section back a bit , they are meant to have a step down in diameter just outside the shroud , i think I've made it too far outside the shroud by maybe 3 or 4 mm ,anyway you get the picture.

[Harrison]

Re: Sten mkII to mkV conversion project

That's amazing work, keep us all updated with its progress

[dadio]

Re: Sten mkII to mkV conversion project

One barrel complete with bayonet lugs .

[dadio]

Re: Sten mkII to mkV conversion project

This may not look like much but it took a disproportionate amount of time and several attempts to get right . what it is is the plug connection between stock and gun , it uses mini deans plugs that mate as the stock is fitted in the normal way ,it's not much to see yet , only 4 pieces of metal but accuracy is vital to get a good mating and a rigid stock fit .the long and short pieces will be welded at a right angle once a couple of other cuts have been made for the wood grip fitting and trigger to go through but you should get the picture .

[dadio]

Re: Sten mkII to mkV conversion project

Little more done today , the lower receiver parts are welded together ,fiddly work getting it all true even as the weld cools ,cut the holes in the bottom for the grips and trigger , again it looks very little but it takes ages to get right and i had a fit of procrastination as well .The grips are held in place by a single screw and are located by the raised square in front locking into a square hole in the metal.

[dadio]

Re: Sten mkII to mkV conversion project

Trigger guards cut off the old trigger housing to be re used , the shape of the mk5 trigger guard is slightly different and has a wider radius corner at the front so they had to be modified slightly , fiddly again making two the same but it worked in the end and they are now welded on , now i have this done i can find out exactly how much shorted the front section of the trigger housing needs to be ,this all needs to be done before i make the sides , on the agm version the lobes that are screwed onto the tube are part of the front trigger housing and that's wrong ,they should come out from under as part of the rear section side panels and that's what i'll do so everything else has to be done first .

[dadio]

Re: Sten mkII to mkV conversion project

I found a couple of hours today to shorten the forward trigger housings, on the mk 5 the rear part is stretched to give space for the pistol grip and so the front must be abbreviated so it was cut ,weld and grind time .The pictures show the modified front section's in place and next to an unmodified example .
Now that this is done i can also weld in the sides above the trigger guard and grip ,there's not a whole heap to do now ,just the trigger system to move forward ,the end cap return to weld on ,the sides to weld on the trigger housing ,paint and a load of sundry things to finish off.

[dadio]

Re: Sten mkII to mkV conversion project

The first rear trigger housing has its sides complete with the tabs that would be welded to the main receiver tube,though they will be screwed for this airsoft version as otherwise the gearbox would not be removable ,unavoidable I'm afraid but they will not be Phillips screws ! , you may notice it has two sets of tabs ,two at the front as usual and two at the rear that you only tend to see on the mk5 ,you might also see that I've cut the tabs off the front section where AGM decided to fit them ,i have no idea why they did that as it could have been done correctly with no additional effort ?

[dadio]

Re: Sten mkII to mkV conversion project

Hello again , been doing a few more little bits yesterday and today , nothing earth shattering but bits that needed doing or correcting .
I have both trigger housings welded together and all the mounting holes drilled ,countersunk and the old holes in the front section that are no longer needed welded up , so next on the list is moving the triggers forward to their new position , this meant milling out a new channel in the motor mount's and abandoning the old switch system as it cannot be moved forward as too much metal would be taken off the motor mount and the switch cannot stay where it is as it fouls the stock mounting hook , this is no bad thing as the old switch was a crappy design that used the alloy trigger to bridge out the switch contacts , so what will i use for the switch ? i have a pair of 15 amp micro switches that will be remotely fitted in front of the gearbox inside the trigger housing and operated via a rod much like the trigger on the agm mp40.
this first picture shows the old and new positions of the trigger in the motor mount.

and this second one shows the position when in place in the gun.

now i have the trigger position set i can make up the wire loop/hook looking part that would be the axle for the trigger in the real gun.