Thursday, January 18, 2024

The 450 Rigby Part 2

I'll let D'Arcy pick this up again

The action work began with addressing the bolt. After indicating the part in the lathe, I began by opening the bolt face from the standard belted magnum diameter to the larger diameter of the 450 Rigby rim diameter plus .005”. With this operation complete, the bolt was removed from the lathe and transferred to the mill. Inverted vertically in a dedicated fixture, I carefully re-contoured the surfaces to allow the larger cartridge case rims to roll in under the extractor hook and into the bolt face as the bolt pushed the cartridges forward and out of the feed well. 

The FZH-supplied extractor was then modified with a few select needle files and reshaped to work in harmony with the bolt face and the provided Norma brass. The function of this operation alone is what gave the claw extractor system the street cred that it has had since day one. Done improperly, it either retards feeding, or worse, renders the entire system into a push-feed receiver. I allowed .005” to .007” of extractor tension applied between the hook and the extractor groove of the case, once I had everything correctly timed. The carefully contoured face of this extractor and the added clearance machined in the extractor slot side of the receiver allowed the bolt to be closed over a round dropped directly into the chamber and will give the shooter one additional round in total capacity.   

The OEM-supplied FZH bolt handle was removed and a new bolt knob that had been previously checkered and engraved was installed. Traditional big-bore aesthetics aside, I prefer to sweep the bolt handle to rear by about 15 degrees.  The client agreed.  “I think it looks better,” L.B. told me. “But, more importantly, it shortens the length from grip to bolt face which makes bolt operation easier, and much easier under stress. 15 [degrees] is about right for aesthetics and function.  Moving the bolt head any more to the rear risks bumping the strong hand trigger finger knuckle under recoil.”  

The notch for the modified bolt handle root or base was then machined into the correct position, angle and depth to allow the bolt body to align the recoil lugs into the required vertical 6 and 12 o’clock positions when engaged with the recoil seats within the front ring while in-battery.

Now, it was time to modify the receiver. As requested, the topside of the completely annealed receiver had been machined for a 375 H&H-length cartridge. This allowed me maximum flexibility since it’s far easier to remove steel than to add it back on—I never was much of a welder. 

Snaking rounds into a magazine as one is back peddling and trying to reload when a situation goes south is not as exciting as it sounds. It was necessary to create a system that was easy to load under stress, which meant opening the ejection port to the correct dimensions. The 450 Rigby cartridge is typically loaded to a 3.750” overall length, so the ejection port and rear bridge on this receiver were modified to allow a loaded round of this length to be loaded easily through the top of the port or the extended left side of the of the receiver. Almost 1/8” of material was removed from the rear bridge alone. I also wanted to remove the front square bridge to allow the rife to be carried with one hand and not suffer the pain of those four corners getting in the way.

     From the mill to the surface grinder 

     The receiver was then returned to the milling fixture with the bottom side facing up. If there was ever a time to measure five times and cut once, that moment had arrived.

    A longitudinal slot was machined through the feed well and into the bolt raceway that would soon be wide enough for the 450 Rigby round.

 To allow me to set the magazine assembly on the receiver, I had to cut the slot for the rear standing tab at the back of the mag box first. This tab centers the magazine box opening directly under the receiver’s feed well so cutting this cavity required attention to detail.

        Tooling was then selected to plunge through the bottom side of the receiver and into the bolt raceway. At this point, the phone gets placed in the car and the shop door is locked. With a variety of standard and ball end mills, the correct depths and tapers of the feed well, angles and radii were then established.

    With the slot cut to the correct depth and width, the assembly was able to sit flush on the receiver. With both guard screws finger-tight you could visually see and lay out with a scribe the edges of the inside of the magazine box. These edges were used as a reference to compare with the crib note diagrams that I may or may not have scribbled on a napkin.

    The magazine box was installed over the feed well one last time to make sure all the required steel had been removed. Only then was the receiver removed from the fixture. 

 Now a mandrel was screwed into the receiver and, with the mandrel held in the bench vise, I begin to use mold making stones on all of the machined surfaces blending and removing the machine marks and smoothing the transitions. 

At this point, it was time to install the barrel by indicating it in with a gimbal set up ala Hambly-Clark, Jr. This precise method has become the only one that I will use in my shop to thread, fit and chamber a barrel. I would be using this chambered barrel to set up the feeding while the bolt and receiver were still in their annealed state. The chamber was cut with the Henriksen reamer and intentionally run .008” to .010” deeper than required for the feeding process to be begin. Later, the barrel would be set back to establish the proper headspace after the heat-treating process of the bolt and receiver had been completed. 

With the barrel now installed hand-tight, I attached the bolt stop, the completely assembled magazine, the newly fabricated follower and a generic w-shaped magazine spring. I begin to run dummy 450 Rigby cartridges from the magazine into the chamber. The bullet ramp was addressed first using rotary carbide burs, then rotary stones followed by needle files and experience. Test feeding and fitting began with one cartridge at a time coming off the follower first, then two at a time, and continued until the entire loaded magazine would feed. During this exercise, I also determined the best magazine spring to use with this cartridge payload. Not all springs are the same-- not all of them collapse or shift forward and rearward the same and, using a large selection of springs, I tried and eventually found the best spring for this application. 

It is important to pay attention to how the cartridges leave the mag box, where the bullet nose first engages the bullet ramp as well as the path that the bullet takes as it travels up the ramp. If you begin this procedure with a spitzer or round nose and you believe you’ve got your mag box, feed well and rails just like you want them. It’s now time to make up a complement of flat-nose dummies and run these through your receiver group.This can be quite humbling on the first go round. I prefer to use the Barnes Flat Nose Solids as my dummy bullet standard.

If and only if, these flat-nose rounds behave and show no resistance when being run into the chamber at the same speed that you might use at the range, then it’s time to move onto the next phase. 

Next, the bolt body and receiver as well as the striker, safety wing and bolt shroud are hand polished to a 220-grit finish. These nicely polished parts were sent off to be surface hardened in a carburizing process. Only then, once all of the components are at their final hardness, do I dare run the bolt at speed to allow me to do the final feed work. This "at speed" test is ultimately separates the chickens from the pigs. In the words of one of my favorite bands "It's a long way to the top if you want to rock and roll"