The cordite charges used in the original development of H&H magnums were heat sensitive and kept reasonable for the expected hot climates they were designed for.
I agree with the second part of your statement, but the first part is derived from “gun writer” wisdom. I have not seen any data on the temperature sensitive of cordite from period American gunpowder. As far as I can tell, there was no difference in temperature sensitive in period cordite versus American stick powders. They all were bad. I highly distrust American Gunwriter “wisdom” as these characters don’t actually test or verify any of the “wisdom” they endlessly repeat to each other in their ignorant and inbred community. Unfortunately their statements are unquestionably taken as gospel by the American shooting community, who then repeat it until it becomes an object of faith. The only cartridges I fired that had cordite were 303 British service rounds,. I am of the opinion that American Gunwriters are as equally ignorant of the pressure characteristics of cordite as I am, and, their opinions are based on nationalistic biases. I have read a lot of American nationalistic rubbish from American Gunwriters over the decades. It was particularly virulent in the pre WW2 era.
What we do know is that British cartridges loaded with cordite were used world wide, in Arctic to Desert Environments. So were American cartridges loaded stick powder, and of course ball powder, which caused a lot of jams in hot and hot/wet environments. Maybe the 5.56 cartridge should have been loaded with cordite.
Remember around 5o,ooo CUP is now known to be about 60,000 psi or so. The head size and there fore thrust area of those old cartridges was huge too.
You have no idea nor can you state what pressures those British proprietary cartridges operated at, nor what pressure specifications they were kept under. There is an interesting article on British sporting cartridges in my Cartridges of the World. Unfortunately no pressure data, but the author brings out the point that British cartridge pressure was kept low, very low by American standards, for several reasons. Almost all Magnum cartridges were used in break open actions. These actions are similar to double barrel shotgun actions and are not particularly strong. They are a lot less rigid than a Mauser action. And another reason was that the British were aware that temperatures raised combustion pressures. Unlike the Americans who are fairly clueless about this issue. So the British started out with low pressure cartridges that would not get overpressure in 100 degree heat. They wanted their cartridges to extract in hot conditions, particularly those cartridges used on dangerous game. American cartridge practice has generally ignored temperature and pressure and focused solely on maximizing velocity. Gunwriters think nothing of 65,000 psia cartridges, think nothing about pressure problems, they are only focused on shilling, and velocity is an easy characteristic to shill about. However, pressure is not your friend. It is better to do the same job at low pressure than high. There will be less problems. High velocity generally equals high pressure, especially in cartridges less than 0.50 in caliber. The author of the Cartridges of the World article claimed a number of shooters had extraction difficult with their 458 Win Mag’s, and got stomped or eaten when hunting dangerous game in hot weather.
The reason this is not well know is because few American’s hunt dangerous, large game, in hot weather. Most of the big game rifles they own are gathering dust in gun cabinets. I doubt any have been fired enough to wear out the barrel. So their opinions are formulated on the basis of maybe twenty rounds at the range and decades of Walter Mitty dreams. Similar to your situation, your FN Mauser action is more of a Rorschach ink blot test than anything else. The rifle and action are around 70 years old, you have never fired any rounds through the thing, (apparently) and yet, you project all sorts of feelings and emotions about the thing.
Well, shoot the thing. Shoot it with hot Weatherby loads. Shoot a lot of rounds through it, wear out the barrel, and come back and provide some data on the lifetime of the thing.
I for one, would rebarrel the thing to something else.
The MKV Weatherby action while theoretically very strong in the field has shown it self to be not as great as expected, one very big problem is getting all those multiple locking lugs to bear against their engagement areas equally . as one example of "improvements" that have not measured up.
There are lots of rifles with multiple locking lugs, I have never owned a Weatherby. The analysis by Stuart Ottesen in his book "The Bolt Action", Chapter 10 Weatherby Mark V, raises this an an issue. However Stuart wrote this book in 1976, well before the semi conductor revolution. I am certain that today's manufacturing technology would have no issue with achieving 100% lug contact with all lugs (for a price) , something that could not have been done with the single process milling machines that were on the factory floor in 1976. Lugs were probably filed to fit, if fitted at all, back then. The greatest issue I can imagine is heat treatment warpage, but, the lugs could be precision ground after heat treatment.
The strength of a Mark V action is almost unbelievable.
Wiki states:
https://en.wikipedia.org/wiki/Weatherby_Mark_V
Proof testing of the Mark V action
Weatherby had intended that the new action would be the safest and strongest bolt action available. The rifle was marketed as the "The World's Strongest Bolt Action". The Mark V action has been tested to be able to contain up to 200,000 CUP (Copper Units of Pressure).[5]
The testing of the rifle was conducted on a production rifle chambered for the .300 Weatherby Magnum. Before testing was to be conducted, very thorough measurements of the rifle were taken so as to provide a benchmark for the testing which was to be undertaken.[6]
The first test was conducted using a 180 gr (12 g) bullet propelled by 82 gr (5.3 g) of Du Pont #4350 powder. This load provided 65,000 psi (4,500 bar) of pressure. This load did not show any pressure or extraction issues with the new Mark V action but caused a slight sticking of the cartridge case in the Mauser style rifle design. Subsequent testing was performed using the same 180 gr (12 g) bullet and using a powder charge of Du Pont #4350 which increased by increments of 2 gr (0.13 g) for each test thereafter.[3]
The second testing which was conducted with the 84 gr (5.4 g) showed no signs of pressure nor issues with extraction even though the measured pressure was close to 75,000 psi (5,200 bar). Firing this load in the Mauser rifle led to a blown primer and extreme difficulty was experienced in extracting the spent case.[3]
Using 86 gr (5.6 g) of Du Pont #4350 the cartridge began to show signs of pressure in the Mark V action. However, the case did not stick and extraction was performed easily. Breach pressure was found to be between 85,000–95,000 psi (5,900–6,600 bar). Measurements of the spent case showed that the case had stretched at the belt a mere .0005 in (0.013 mm).[3]
The spent case from the 88 gr (5.7 g) test led to a slightly sticking case, which in turn led to a slight difficulty in opening of the bolt. Measurements from the case belt showed that the belt had expanded from .533 in (13.5 mm) to .535 in (13.6 mm). The pressure generated by this load was 100,000 psi (6,900 bar).
The fifth test was conducted used a load of 90 gr (5.8 g) of Du Pont 4350. Firing this load led to some difficulty in opening the bolt, and the case was extracted when opened. The belt of the case still measured .535 in (13.6 mm). A difference in the diameter between the bolt head and the diameter of the barrel of .002 in (0.051 mm) per side was noted. No bulging of the bolt, receiver or the barrel was noted. Headspace was measured to be the same as prior to the testing.[3]
Further testing was conducted with a 180 gr (12 g) bullet lodged into the throat of the barrel. A cartridge loaded with the standard charge of 78 gr (5.1 g) of Du Pont 4350 and a 180 gr (12 g) bullet was fired into the back of the first bullet. It was found that both bullets exited the barrel. The primer had been pierced and the exiting gas entered into the bolt and hit the firing pin sleeve, which was loosened slightly. The bolt was opened by hand but the cartridge stayed stuck in the chamber. When the case was tapped out, it was found to be in good condition except for its pierced primer. It was found that the barrel, just in front of the receiver ring, had expanded from 1.147 in (29.1 mm) to 1.1496 in (29.20 mm). The diameter of the bolt head had expanded from .7178 in (18.23 mm) to .7190 in (18.26 mm). The head space had increased from .2163 in (5.49 mm) to .2174 in (5.52 mm). All other dimensions had stayed constant. This test was conducted 15 times. A test was conducted with a 220 gr (14 g) bullet lodged into the bore of the rifle and a 180 gr (12 g) grain bullet was fired into the back of this bullet. The result of this test found that the cartridge case head had expanded to .545 in (13.8 mm). After these additional 15 tests it was found that the head space was set back only a mere .001 in (0.025 mm).[3]
While I am a fan of the pure 98 Mauser action, it was too expensive to manufacture. The FN Deluxe action had a lot more Mauser features than the later FN actions, but still, they split the inner collar, which I think is bad for strength and gas sealing. The later actions, about the only thing Mauser was a claw extractor and the contour. Weatherby continues to make Mark V actions, which ought to be a comment on how well they have been accepted by the shooting community.
But will sell it .
