A bit more progress on the WOMBAT.
I fabricated the front A frame from steel sheet and the carriage is now complete ready for painting so I started on the barrel - this is 3 different diameters and made from 2 sizes of aluminium tube 127mm and 152mm - I cut 40mm out of a legth of 152mm and re-welded it to get a piece of 140mm to make up the mid section then welded them all together. The trunnion carrier is a piece of 160mm steel tube that used to be an air drier receiver I had lying around - knew it would come in handy one day!
I fired up the furnace to melt down some more old pistons and cast a lump of aluminium I could machine into the breech locking ring and then rolled up a cone of 1.5mm sheet to create the venturi tube - difficult to roll a cone by hand so it is a bit square sided - I will have to turn a wooden plug to go inside so I can hammer it a bit more true.
The locking collar for the breech is fab'd from 10mm plate then filled with aluminium so I could machine the grooves inside - just needs the hinge assembly adding now - this is quite complicated as one swing of the opening handle simultaneously turns the locking ring, retracts the firing pin, extracts the shell case and locks the ring into the closing position so the teeth engage correctly.