Now on to breech details!

As pointed out at the very start of this article, the left hand side of the breech block is glued on wrong, at least it was on my Pak. The notch should face towards the front of the gun, not the rear, as shown in this photo of the real McCoy. This picture also shows the trigger charging and trip arms, as well as a mounting bracket that holds a short trip lever transmission rod in place.

 

 

In this photo you can see that the left side of the breech block has been turned so that the notch faces to the front, the trigger charging and trip arms have been added, and the breech filled with resin to fill the void area where the trigger arms do not move. The trigger charging and trip arms were created by taking a Xerox copy of the real breech block and enlarging it until it was the same size as the molded breech block, cutting the pieces out and tracing the outline on plastic stock. The trigger charging arm hand grip was cut from the existing block and glued onto the new trigger charging arm. The trigger charging and trip arms are held in place by a bolt tapped into the side of the breech. Another detail added is the small plate set into the side of the breech. In order to make enough room to mount this plate, a small strip of plastic was cut, glued into place and the remaining crack/separation line filled with contour putty so it could be sanded smooth and painted to look like one solid, flat piece.

Now on to the gear box details…

The following picture of a real Pak 40 obtained from Tanxheaven Reference pictures shows a number of details not present on the 21st Century Toys model. To begin, the gear box is held in place on the cradle in part by a tab through which a bolt passes to hold it in place. The outer edge of the gear box looks like a tube with a flange through which the drive shaft for the gear box passes, and is attached to the gear box by four bolts. Additionally another plate, with the electrical firing device connection, is bolted on the end of the gear box.

 

 

This picture shows my modified gear box. The gear box is attached to the side of the cradle by a bolt that passes though a fabricated tab set into the back of the gear box in a notch so the gearbox will sit flush against the cradle. In order to make it appear as if the left side of the housing is a separate place, a line was filed into the housing, the corners rounded and bolts set into the corners to make it appear that they secure the plate to the housing. A section of brass tubing was used to enlarge the tube that leads to the flange, and an additional plate, through which the firing wires pass, was fabricated and bolted in place on the end of gear box with four 0-90 bolts, only two of which are installed in this photo. Also visible, is the fabricated oval anchor plate for the elevation wheel, which is held in place by an 0-90 bolt and nut, as well as the removed gun guard shield mounting brackets, which were notched and bolt holes drilled so the new gun guard could be bolted in place like the real Pak 40.

Trigger mechanisms
I have not found a field manual on use of the Pak 40, but from all of the reference pictures it appears there were two methods of firing/triggering the Pak 40. One was an electrical charge, which was activated by depressing a button in the center of the traversing wheel (and hence why the wiring harness passes out of the connection on the end of the gear box). The other, more definite triggering method was a lever mounted on the side of the gun slide. It appears the electrical trigger often failed to fire the gun, but the mechanical trip mechanism almost always worked. This mechanical lever had a finger hole through which the index finger could be inserted or a lanyard attached.

 

Picture of a real elevation wheel with electrical firing button in the center of the wheel.

 

 

Picture of a real mechanical trigger lever; it could be activated by depressing the lower end or pulling on a lanyard tied in the upper hole in the lever. You will also note in this picture the plunger on the top of the box that trips the breech block trigger arms.  Also visible as well  is the electrical wiring harness that enters the trigger box at the rear.  This harness comes from the gear box connection shown earlier.

21st Century Toys has the trigger lever molded on the side of the trigger box; this was sliced off the box, a hole drilled in the upper end, and the lower end filed off to resemble the trimmed down lower end of the real lever.

 

Trigger box under modification. The trigger lever was sliced off the trigger box, a center hole drilled for a pivot pin, which was a brass brad passed through the lever and a small brass tube spacer into the trigger box. The wiring connection was created by using a small bolt, in the head of which a drill hole was made to receive a wire. The bolt was threaded through a larger nut and a small brass spacer (same as what holds the trigger lever out from the trigger box) and anchored into a tapped hole. At the very top of the picture you can see the added strip along the bottom edge of the breech and the inset anchor plate that will hold a short transmission rod that activates the trigger arms on the side of the breech block. The push rod has not been added yet to the top of the trigger box. The push rod was fabricated from a brass brad filed to represent the shape of the push rods I have seen photographed, and a short section of tubing through which it passes into the trigger box. Also visible, on the right edge of the photo, are the small 0-90 bolts and nuts used to anchor the guard bracket (turned upside right as pointed out at the beginning of this article) back to the gun carriage.