OK, many thanks for the encouragement from everyone who has so far commented on this project so far. So here is the second installment, the SpaS conversion to the grenade launcher.
This purchase was a little on the steep side at nearly £60.00GBP considering the few parts required. It is possible that a cheaper version is available or purchased second-hand.
Any way, enough waffle......Here is the build.
As it arrived, purchased from the same source as mentioned previously.

The two parts required are the barrel cage and the slide grip.

The slide grip needs to be cut down as shown.

Next the ejection port needs to be cut into the cage side. TAKE CARE---Make sure the port is cut into the correct side of the cage, I cannot stress this to strongly. ( I am fortunate to Have a Snow Wolf M41A PR as reference, so I hope the these images are useful).
My ejection port is slightly more square than the Snow Wolf's and was cut in using my trusty dremmel, then sanded.
(In hindsight I shoud have filled the two slots in the cage and cut the ejection port more acurately.)

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My mommy always said there were no monsters, no real ones... but there are.

The next job for the dremmel was to cut the ejection port relief into the slide grip. Slip the grip onto the cage and mark where the slide covers the eject port. Be aware at this point that the slide only has two runners as the rejected part of the slide has the other two. now cut out the relief.

With the eject relief cut out the slide now only has ONE runner, so it is essential to glue in two new ones.

The launcher barrel sleeve and magazine tube are made from 34mm uPVC waste pipe. The top barrel sleeve is cut to length from the eject port to the end of the cage, and the mag tube the full length of the cage. To make them fit inside the cage the mag tube needs to have a strip cut out down its full length and then glued to the barrel sleeve (I used a hot glue gun for this).


Using the dremmel yet again I cut a thin slit into the bottom of the mag tube that corresponds to the loading port underneath the cage from the front but NOT all the way back (approx 2/3rds)

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My mommy always said there were no monsters, no real ones... but there are.

The sliding breech is made from the same uPVC pipe and is just slightly longer than the eject port. To this I added a thin strip of pipe to act as a spacer and a longer and wider strip that is about the same length as the loading port aperture in the cage. These I glued and drilled and screwed together.
Drill a small hole in the strip approx. 2 cm forward of the leading edge.

The barrel and breech are made from 28mm uPVC pipe. The breech should fit at least 2 inches into the barrel sleeve and extend backwards but not beyond the hole it in the top of the cage and a section cut out the same length as the eject port. The barrel muzzle is shorter but long enough to fit at least 2 inches into the sleeve. I wrapped insulation tape round these parts to get a tight fit. DO NOT glue at this time.

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My mommy always said there were no monsters, no real ones... but there are.

OK the tricky bit......making the sliding breech work....
I used a piece of wire cut from a wire coat hanger and made two right angle bends in it so that it was 3.5cm in height (unfortunately like a complete tw*t I forgot to take a photo prior to fixing) however I twisted the bottom through 90 degrees so that it fit in the bottom of the grip with the top bend facing towards the breech and fixed it in with Milliput body filler LEAVE TO CURE.........PUT IT DOWN

Now slide the whole barrel, breech mag and sleeve assembly into the cage from the front.

Tricky bit #2 Insert the wire hook on the grip into the small hole drilled in the long strip under the sliding breech and snap grip into runner grooves.


Attachment point, White 5mm plastic spacer, cut down chucky block and screw, DO NOT GLUE at this time.

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My mommy always said there were no monsters, no real ones... but there are.

The chucky block acts as a stop for the sliding breech.
From an off cut of the 34mm pipe I cut and shaped using the dremmel a piece that is the same shape as the loading port under the cage.
Now measure the distance of travel of the sliding breech connector (Special Part# 3548-489C/A23) from the closed position to the open position where the grip relief lines up with the eject port, then cut a thin slit from the front of the piece to the point where the breech is fully open. this acts as a stop for the slide.

This will eventually be glued in place.

The build so far.........




If anyone has any questions or would like further info/explanation please let me know and I will do my best to ammend my process descriptions.

Transmission terminated

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My mommy always said there were no monsters, no real ones... but there are.

Your innovation and attention to detail is very impressive!

If I might make a suggestion on the shrouds, since you are scratch building them I suggest not fully copying the Snow Wolf template. There are some inaccuracies that you can easily fix.

The 3 most glaring are the height/squareness of the rear top, the length of the counter space (which in turn makes the magazine housing too low), and the 'trapezoid' on the front bottom (which is too centered).

This is how I modified one set, but in your case you can avoid those issues all together by just tweaking the template drawing.

Many, Many thanks, I think it might be a bit too late on this build as I have already cut two of the pieces of ABS. However I have a load of foam board that I will make another shroud out of to your specs.
Hope my photos and relevent descriptions are helpful and easy to follow.

Cheers

Transmission terminated.

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My mommy always said there were no monsters, no real ones... but there are.