MP28 Part Three

Custom builds, MP28, Sub Machine-guns, Weapons, WWI

At the end of the last post, I had the receiver tube cut, the stock made and a gearbox partially modified.

 

_DSF5397 _DSF5388 _DSF5577
Since then, I have realised that the receiver tube isn’t quite right, the gearbox modification is a pain in the neck to get working and as a result the stock is too shallow to take the gearbox in its native configuration. This has put the project back a bit.

To save time and get a working gun I am scrapping the modified gearbox. I will keep the incorrect receiver tube for now and treat it as a prototype so that all the parts fit and the newer correct one leaves the workshop clean and not abused.

On to progress!

The new magwell is very slick and the mechanism is really solid in comparison to my first attempt. For those who don’t recognise them, the magazines are identical to those used for the Sten and MP40.

 

 

The next step was to fix this to the receiver. At this point though I say so myself I am quite good at rolling and bending steel accurately! I rolled a collar in steel around a spare piece of 38.1mm tube (the same as the receiver tube).

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This could then be tacked and welded in place.

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Some work with a hammer later, I managed to get it off the tube former and polished it inside with the drill drum sanders I have for jobs such as these. I kept going until it fitted just on the end of the receiver tube with a little friction.

_DSF6121

In order to get it all the way down the required location, I also had to take a sheet of wet and dry paper and sanded the receiver tube down. The main issue was the little rises around the cooling holes (you can see the little white rings in the photo below).

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With a little work, it slipped on comfortably._DSF6124

As you can see, the holes are not perfect, but they will also be invisible once assembled. I wanted to give a little extra space to ease aligning them.

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I could then clamp the magwell to the tube and tack it in place with the MIG welder  to test it before going to town and welding it permanently in place.

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I’ll grant, not that pretty yet. With jobs like this I like to leave plenty extra weld on top so that I get minimal porosity on the part that will be visible when I grind it smooth into shape.

 

And ground and polished roughly into shape:

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So, progress is slowly being made. At least I have been able to discount a few options in this deign and I have a nice spare stock! Hopefully this build should speed up a little now as I have done a lot of the design work for the improved version.

MP28 Part two

Custom builds, MP28, Sub Machine-guns, WWI, WWII

At the end of Part One, I had the two main external components at hand:_DSF5389_DSF5397

The receiver tube and the stock have been roughly cut, so most of the work to do was internal. I designed a custom hop unit to fit inside the receiver and feed the BBs back from the magwell to the chamber.

_DSF5520 _DSF5521

I sent off the orthographic drawings to a guy who can do 3D CAD work and he converted my designs into a digital model before 3D printing it in ABS. It looks smashing, far better than I ever expected!

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A bit of filing was needed to fit the hop in the tube, combined with a light tap with a small hammer and it was seated in place. A piece of barrel sits in the space in the side to engage with the magazine.

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_DSF5550The outer barrel is a piece of tube sat in the centre of the cooling jacket. Welded at the front and back are two steel rings to suspend the tube and at the front is the perforated front cap.

_DSF5552

Another little tap with the mallet and bingo, it fits very nicely!

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The rear cap has a space to take the locking latch, which is sprung with a tension spring. There are two screws in the edge of this back cap to secure it in place, though I may put another in the top.

_DSF5574

This latch then locks into the locking unit on the stock.

_DSF5564The rear sight functions much like the original, it is basically a miniaturised version of the sight I put on the MG08/15 with a ramp providing elevation adjustment and the leaf moving left and right for windage.

_DSF5563

There comes a point where you have to just try and fit the gearbox! Inevitably somewhere in your designs something will come a-cropper, in this case I forgot to factor in the nozzle position being at the top, not the centre of the cylinder casing. As a result the stock would have to be about 10mm deeper to fit the gearbox. Given that I have already made the stock this isn’t a great option! I plan to get a custom cylinder head made so that the nozzle is in a more convenient place.

_DSF5575 Also to save space I have conducted a little modification to the gearbox externals. The motor cage in most V7 gearboxes is angled down slightly to fit in M14 models. This is great if you are building a rifle, not so much for this project!

_DSF5577 My first thought was to build a whole custom motor cage but this would be a huge job. Instead I modified the original cage so that it sits slightly angled up. The motor came into contact with the back of the spring casing before it could be secured so a little material had to be removed from there. As you can see from the photo above, the trigger and a part of the fire select has also been removed.

_DSF5449 _DSF5561

The stock also needed a bit of space cutting out to take the gearbox. The shape eventually had to be quite complicated to take the wire guides on the side.
If this post has inspired you to want a project of your own, email us at enquiries.vintageairsoft@gmail.com. You can get regular updates on Facebook as well as here.

Still to come! Trigger unit, gearbox mounting and the magazine housing.

MP28 Part One

Custom builds, MP28, Sub Machine-guns, Weapons, WWI, WWII

It has been a while since I posted my introduction to the MP28 and quite a lot has happened since then!

Most of the parts needed are in now and components progress is going well. There are lots of photos of this project so you can see it progressing nicely.

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I had the magwell cut with the last batch of laser cuttings and welded it quite a while ago. As you can see, it fits snugly against the tube used for the outer shell of the gun.

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The fore-end of the MP28 is heavily perforated for cooling. This required a very precise set of measurements and I decided it would be easiest to draw out a 2D representation in Qcad. I then printed this out and taped it to the tube in the right place. A centre punch in the dead centre of the circles allowed for accurate drilling.

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I drilled small 4mm pilot holes first, then holes to the full size. In the photo above you can see the second drilling in progress.

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Drilling finished!

_DSF5391A bit of work on the stock next. Having marked out the template on the wood, I cut the straight lines with a circular saw. The more complex area around the pistol grip I cut freehand with the router. This did however leave me with a little excess wood still holding the whole unit together.

_DSF5393

Drilling through weakened the area considerably. Only a little work with the chisel was needed to free the piece.

_DSF5394

Separated. Once the excess was cleaned off I could start shaping in earnest.

First shape was done with the electric plane, a favourite tool of mine. Finer detail and smoothing was achieved with a hand plane. Working in and around the pistol grip, the half-round file did a fine job.

_DSF5397Finally, where the stock is at now. I’ve inhaled most of the wood removed today so it’s time to take a break! A bit more work with the mini sander and this will be as smooth as a baby’s bottom. That will have to wait until the action is fitted though as it is likely to sustain some bumps by then.

It is only when you have all the components together that you realise how big this gun is. When most people think of a sub-machine-gun it is a compact firearm for close quarters. This is nearly 90cm (three feet) long. I guess they had to start somewhere to be fair though!

More to come soon on this! If you have any questions email me (Dom) on enquiries.vintageairsoft@gmail.com or leave a note in comments.