I posted this in the 500/416 thread but I'm double posting to share with those who have no interest in that cartridge:
I have a Krieghoff Classic Big Game in 500/416 and developed load combinations for which I've logged in data for each shot I’ve taken. The rifle was regulated to 2” at 50 meters with Norma factory ammo with 410 grain Woodleigh bullet at 2325 fps average muzzle velocity. Krieghoff’s regulation standard is both barrels hitting within 3” at 50 meters. To me this isn’t great regulation but I admit that for a 25 yard shot at an elephant of 50 yard buffalo, it is good enough. I have loaded several different 370 and 400 grain bullets that regulate within a 3” spread at 50 meters. Nothing wrong with my rifle…
Being a typical American infected with “magnum-itis” I wasn’t happy with my 2325 fps 500/416 loads producing only 4800 ft lbs of energy. I must have 5000 or else! Other examples of magnum-itis result in buying a 505 Gibbs. Thankfully I haven't gone that far but I do have a 450 Rigby...
At the top end of the velocity range my loads pushed 370 Cutting Edge Bullets Safari Raptors and 400 Nosler Partitions to 2450 fps and 400 gr CEB Safari Solids to 2425 fps. Needless to say those loads did not regulate to the 3” at 50 meters in my Kreighoff. The cases showed no visual signs of pressure being too high except a thin, faint ring around the case just ahead of where the case head started to increase in thickness. The ring indicated the cases stretched resulting in the case wall thinning at the ring. Measuring those cases some thinned only a thousandth or two of an inch, others were more than 5 thousands thinner than the case wall a millimeter ahead of the ring. The .002” or less thin under the ring I will mark and load once or twice again but not for maximum loads. Any cases that thinned 5 thousands (.005”) or more are taken out of service. I may however use some of them for dummy rounds.
Warning: Load cases to maximum level two or three times and watch out! You may have a case head ejected with the case body sticking in the chamber. There are those of us who have and those of us that will…
I measure all my 500/416 cases with case wall / concentricity gauges as shown below. Photos are of an old Creighton Audette made concentricity / case wall thickness gauge and one from NECO. The NECO are in production if anyone is interested.
I used stainless steel rod to make the anvil for inside the case since the gauge didn't come with any. The gauges were made to measure neck wall thickness. For case wall down thickness measuring, I crudely made (since I am not a machinist) rids with anvil ends. For those, I bent the rod, cut off excess, and ground the head into an anvil. It works!
I do not look for actual thickness, rather I measure looking for changes in case wall thickness. When a 500/416 stretches, there will be a thinner ring just ahead of the case head. The gauge needle will dip down from the case wall just ahead of the drastically increasing thickness of the case head.
If you do not have a modified case wall thickness gauge, just look for the ring ahead of the case head. The rings indicate stretched cases. Sometimes they’ve stretched by only a thousandth or two. I mark those with a Sharpie and continue to load a time or two at other than maximum loads. For hunting however, new brass only!
What I’ve had to admit to myself during this process which includes over 200 rounds shot during load development is that while 2400 fps and 5000 ft lbs of energy may looks good in my spreadsheet, there is little need for it. The factory ammunition is NOT loaded to current maimum 416 Rigby velocities of 400 grain bullets at 2400 fps. Rather, 500/416 factory ammunition is loaded to velocities of 2300 to 2325. That is near or a little more than the original loading of factory 416 Rigby in 1911. The 416 Rigby of old gained a great reputation for penetration at 2300 fps using old design bullets that most of us would not even consider.
Additionally, 2300 fps is more than the 2150 fps pushing 400 grain bullets from the 450/400. Both the 450/400 and the original 416 Rigby loads have proved very effective on dangerous game. An added bonus of loading my 500/416 to 2300 to 2325 fps is that the brass lasts for a lot more loadings! Not too hard to figure that…
Meausuring case wall ahead of visable ring with old Creighton Audette wall thickness gauge
Measuring at visable ring - notice dial indicator reading!
Measuring just below the ring as case head starts to thicken
Home made inside anvils for measuring case wall thickness
NECO Concentricity and Wall Thickness gauge with instruction manual
