There is a certain mystique that arises with the term big bore and the fact of generating 5,000 to 7,000 ft. lbs. of muzzle energy with the single squeeze of a trigger. The thought of being on a Dark Continent in the midst of large beasts that go bump day or night. Mud brown rivers that hide 6,000 lb. territorial wrecking machines, 1,500 lb. reptiles and tall grass where you don’t meet your quarry until you hear the grass in his belly digesting. Well most of us were born 30 years too late and a bank roll short. But all is not lost. We can still build and shoot the rifles of yesterday and the modern big bores of our own time and with any luck get that trip of a life-time.
Lets try to take some of the myth out of big bores and see if we can’t make some realistic judgments of our own. Lets try to tame the stories of the killer at both ends and see what it takes to make a big bore rifle a realistic proposition. You’ll probably find that once you shoot one of these wonderful pieces of equipment that you will be at the range with it on a regular basis and introducing your shooting buddies to it. You’ll have made the discovery that this is great fun!!
It seems that the large bore rifles that you come across the most today are the 416 Remington, 416 Rigby, 458 Winchester, 458 Lott, 450 Ackley 470 Nitro express, 505 Gibbs, and 500 Jeffery. I have my own wildcat cartridge called the 470 Mbogo that drives a 500-grain .475 bullet at a velocity of 2500 fps. It will be used in this big bore comparison in order to see what effects the added velocity will have during the penetration tests.
In this article we will compare the four calibers, .416, .458, .475 and .510. We will work through bullet penetration tests loading the 450 Ackley to two velocities, 2150 fps to represent the 458 Winchester and 450 Nitro Express velocities and then up to 2380 fps to represent the many .458 wildcat and proprietary cartridges loaded to this velocity. The 470 Mbogo (www.470mbogo.com) will be downloaded to 2125 fps to represent the 470 Nitro Express class cartridge and then back to it’s regular velocity of 2500fps. The 500 A-Square will be downloaded to 2125 fps with a 600-grain bullet for 500 Nitro Express velocities and also at 2400 fps it’s regular velocity. The 500 A-Square will also be loaded with a 525 grain Barnes solid to two velocities to represent the 500 Jeffery and the 505 Gibbs. The bullet weights vary marginally from the original weights but I don’t think this will make any apparent difference. If you were to chronograph these cartridges as they were loaded originally they would probably show a larger discrepancy due to velocity. The extra ten or 30 grains of bullet weight with consistent velocities will be a very close representation of these cartridges. The 500 Nitro Express may gain the most from the extra weight gain of 30 grains. Barnes solids will be used so that the nose shape and long for caliber bullet trend will remain consistent. This should also show the relationship between sectional density and penetration with velocities being equal. We will try two types of materials one being newspaper and the other, ¾ inch plywood squares with a ¾ spacing between them. Barrel rise from recoil will be monitored and measured. All of the rifles used will have the same stock shape and are fitted with large Pachmayr triple X recoil pads.
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