Part of the difficulty in engineering a functional bolt was nesting the Bulldog far enough into the Steyr receiver to achieve the proper barrel alignment, while still retaining enough of the bolt to allow attachment and rotation of the sleeve and cocking lever.  When placed in the proper position, the Bulldog occupies most of the bolt cavity.

Even after I cut and trimmed the bolt and attaching sleeve to the limit of their ability to grip each other, the Bulldog's frame was still too large to recess up into the receiver far enough.  I found that the Bulldog's upper frame would have to be milled to fit properly with the functioning bolt.

The real question was, what did the propmaker on the film do, or perhaps, if I were in his shoes, what would I have done?   If the gun frame were to be modified heavily, would it still be safe?   Ultimately, I concluded the following:

The hero gun was to be a blank firing move prop.   Once modified, the underlying revolver would never be asked to fire "live" rounds again. Blank rounds would reduce the compression load to the gun and its frame considerably.   Thus, all I really would have needed to worry about was the gun’s ability to withstand blanks.   So I concluded milling down the frame should be a safe change.

Trimming the upper cylinder support of the frame should not weaken the revolver by much, if any, and any reduction in strength would be more than compensated for by the lessened shock of the blank rounds.

So, I proceeded to mill the top of the frame down almost to the depth of the Bulldog’s rear sight groove.   The sides were then milled to the width of the hammer slot at the rear of the frame.

These modifications were necessary to retain sufficient the bolt material that a tube fitted to the turned down end would still have enough circumference to grip the rod under it.   The cocking lever could then be fastened to this tube, which would in turn rotate around the rear of the bolt as the lever is raised.   By capping the bolt just behind the lever and sleeve assembly using a casting of the Steyr bolt end cap (with attachment provided by a small 4/40 Allen screw), the bolt could be opened and pulled back with the same action as the original Steyr rifle.

The final step in nesting the Bulldog beneath the Steyr was to mill a round cut into the bolt for the length of the Bulldog’s replacement barrel.   I was able to use one of the scope mounting holes of the Steyr receiver to establish a range of travel by threading a longer set screw that extended into the milled slot, thereby controlling the slide of the bolt and also setting its stopping point.   This guide screw then also doubled as a retaining screw to keep the bolt in the receiver

The stunt prop had a gun barrel that looked simply like a heavy tube.   There are no identifying marks nor any evidence of the characteristic tapering of the standard Bulldog barrel.   We have concluded that the propmaker probably cut off the front sight from the tapered Bulldog barrel and then covered it with an aluminum sheath.   He may have cut a matching (female) taper into a longer aluminum tube; or he may have turned down the tapered barrel to a cylindrical barrel and then fitted a tube over it to avoid having to deal with the taper.   It is equally possible that a Target model Bulldog was used (although this is a less common gun), which is constructed in this very fashion from the factory.   The Target model came with a heavy aluminum sleeve manufactured to a close tolerance slip fit over a thin steel barrel.   The aluminum sleeve included a shroud around the ejector knob and was held in place on the steel liner barrel with a tiny set screw.

Unfortunately, even the Target model barrel is a little short, so the propmaker still would have had to take an aluminum tube or rod and machine it to fit over the rifled steel core.   Either way, the sleeve used would provide the needed metal to drill and tap into for the Steyr receiver mounts and for the front ammo housing bolt that screwed into the underside of the barrel.   As a bonus, these same screws could also help hold the outer sleeve onto the steel liner by extending through the aluminum and set contacting the steel.  Of course, the 6/32 Allen screw serving as a front sight detail on the Steyr could also have served this purpose

From study of the stunt props I determined that the original prop barrel was 0.75-inch in diameter with a 500-thousandths (.50 caliber) bore, so I used 3/4-inch acrylic tubing having 1/8-inch wall thickness for the model’s barrel. The 60-thousandths bore oversize relative to the .44 caliber barrel of the Bulldog   gives a bit of extra clearance.

Once all of the test fitting had been worked out, I proceeded to fabricate the prototype bolt from aluminum and to retool the best of the primary gun components.   Each part was checked and rechecked to insure all would fit together and work in concert, while maintaining the highest level of detail and premium finish achievable.

Molds and casts were made for each integrated Bulldog component: the triggers, hammer, cylinder, cylinder swing arm (also known as the crane), and a modified thumb latch from the Bulldog.

Similarly, molds and casts were completed for the Steyr action, including the bare receiver, bolt end cap, ammo housing, .222 ammo clip (also known as the magazine), and the trigger guard.   Note that the trigger guard and housing are one piece on the original Steyr, but they were separated into two components to create the hero prop gun.

The rest of the detailing for the master patterns had to be fashioned by cutting up one of my existing stunt copies for the basic shapes and details, followed by extensive recreation and sculpting of finer details and features

The master pattern for the left side cylinder cover was made using aluminum tubing and Bondo ®. The right side was made from three side cover castings cut and enlarged to fit, with a cylinder clearing carved out of the underside.

I worked very carefully on these details, using the best stunt prop casting as a guide.  Each master part was crafted to match the fit of its companion on the stunt prop paying particular attention to the placement of the side covers relative to details visible on the Bulldog frame.   The side covers were adjusted to match every detail and fit on the master as compared with the solid cast stunt prop, such as the partial covering of the trigger pins. Every aspect was checked and rechecked to achieve a precise match.

The main frame is, of course, the Bulldog with its trigger guard and pistol grip subframe removed.  To replace the grip frame I used an older stunt casting to section out a frame that matched the outline of the blaster grips.  The master pattern grips were dissected from one of the best stunt prop castings I had.

After cutting away most of the Bulldog’s subframe, I grafted the portion containing the hammer spring rest into the interior of the protoype's pattern grip frame.  This gave me the perfectly proportioned mounting part for the new blaster’s hammer spring.  

Next came the trigger guard.  This step required cannibalizing two guards from castings of the stunt props, which had to be enlarged in order to fit the real Bulldog frame.  The guard had to be sectioned in the middle and additional material grafted onto the end.

Noting that no screw is visible on the exterior of the trigger guard on any stunt castings, and also that the rear of the trigger seems to roll up into the frame by the grips, I engineered a slot and groove mounting system.  Observing that the front of the trigger guard can pass directly over the cylinder swing arm screw, I thought, ‘why not use it to do both?’  So I did.  And I suspect that’s exactly what the original propmaker did as well.

Returning to the stunt prop, I compared the triggers and verified that the rear trigger was identical to the Bulldog, with its characteristic grooves and profile, so this is in fact what was used on the hero prop.   Interestingly, the front one was exactly the same -- just cut down slightly to fit into the Bulldog's frame where the front part of the subframe used to mount.

Concluding  (with the mindset of the propmaker) that I would probably want to avoid drilling into a chromoly steel gun frame, I quickly found I could use the front subframe pin as the new trigger bushing mount.  Next came the new custom pistol grip frame.  Once again figuring that I would not want to drill into the steel frame, I milled the new grip frame to fit into the Bulldog's frame in the same way the Bulldog's subframe previously mounted in the rear.

At this point it was time to begin fitting the Steyr receiver onto the Bulldog frame.  From the stunt prop it was obvious that two 4/40 Allen screws were used to hold the front of the Steyr receiver to the firing barrel.  However, there are no visible screws that line up with the Steyr and the Bulldog frame underneath.

With the center cut away, there was no easy way to mount the Steyr receiver onto the Bulldog , and it is not readily apparent how the propmaker originally secured the rear of the receiver to the revolver frame, either.  The only visible rearward screw is the one just above and to the rear of the safety, but on the stunt castings this screw is too high and could only have screwed into the rear bolt cap.   In fact, I believe this is exactly what that screw was used for – to hold the rear bolt cap (and thus the bolt) in place.  The only option was to engineer a new rear mount for the Steyr.

After careful consideration, I settled on a slot and rail design for the mount.  I cut two slots into the inside walls of the Steyr receiver (one on each side) and then glued two corresponding rectangular rails onto the Bulldog frame.  This may well have been done by the original propmaker,  by either pinning or soldering two like metal bars onto the steel revolver frame of the hero prop.

This design made the Steyr receiver very secure as well as easy to remove.