The overwhelming reason for choosing a magnum cartridge is to gain increased performance over and above what can be obtained from a standard capacity case.
But this must be tempered with the realisation that the diameter of the bore plays a major part in the equation.
A case that may be classed as “magnum” for the 6mm bore may lack sufficient capacity for a .30 calibre. This is true not only with belted cased magnums and the new beltless short magnum variety, but also with those on the standard .30-06 head size.
The .30-06 case certainly has magnum capacity for any bore size up to and including .257, and when used in its many “improved” versions, like the Ackley and Gibbs it can be rated magnum in cartridges having slightly larger bore diameters.
There’s two sides to every story, however, and many cartridges carrying the “magnum” label are not true magnums as far as cubic capacity is concerned.
For instance, the .222 Remington magnum has far less case capacity than the .22-250 and .220 Swift.
Nor do all belted magnums qualify for the title. The 6.5 and .350 Remington Magnums actually hold no more powder than the same calibres based on the .30-06 case.
These cartridges came out in a short action and bullets had to be seated deeply in order to fit in the short magazine, but when chambered in a standard length action and given a longer throat, the 6.5 might conceivably live up to the magnum label, but the .350 barely equals the .35 Whelen.
For this exercise then, we’ll concentrate solely on the big cases - true magnums - which have the potential to live up to their name.
Magnum cartridges appeared on the American hunting scene even before the Western Cartridge Company started loading the British-designed .300 and .375 H&H and Winchester chambered them in their Model 70.
The first beltless magnums were Charles Newton’s large-capacity, high-intensity .30 and .35 Newton cartridges which appeared during the period 1913-15. They were based on a rimless, magnum-type case, but their true performance couldn’t be realised at that time due to the lack of suitable slow burning powders.
The popularity of magnum cartridges offering increased velocity didn’t really take off until the 1940s when wildcatters like P.O Ackley, Powell-Miller, Roy Weatherby and others developed dozens of large capacity cartridges based on the H&H case.
But it was the burgeoning popularity of the Weatherby magnums that made rifle and ammomakers sit up and take notice. This probably wouldn’t have happened then, if Du Pont hadn’t introduced slow burning IMR-4350 powder which made possible Weatherby’s increased velocities.
After World War II magnum cartridges got another boost when Hodgdon released surplus H4831 powder to handloaders. It was used to load .50 calibre cannon shells and was slower burning than any powder previously available.
Hodgdon sold it as IMR-4350 Data Powder because he had found it was safe to use IMR-4350 data when loading it in various cartridges. But it didn’t take long for handloaders to discover that heavier charges could be safely used to obtain even higher velocities than were possible with IMR-4350. By 1950, the Weatherby Guide was listing data for both IMR-4350 and H4831.
With Weatherby leading the charge, magnums literally took the hunting world by storm. Before long, both Winchester and Remington started designing magnum cartridges, and hunters were clamouring to buy magnum rifles that would reach way out yonder and drop the largest big-game animals in their tracks.
Once the initial furore over magnums had died down, the real advantages of magnum cartridges were widely recognised. The main reason for choosing a magnum cartridge is to obtain more velocity from it than you can get with a standard cartridge of the same diameter with the same weight bullets.
This resulted in a flatter trajectory over long distances, and in the case of the big-game hunter, more striking energy out where the game is.
The kind of shooters who gain the most benefit from magnums are the long range target shooter, the varmint hunter who likes to take ‘em “fine and far off” and trophy hunters who frequent areas where the shots are long or who face game dangerous enough to require maximum stopping power.
Factory cartridges for magnums are usually loaded with premium-class bullets which makes them quite expensive, hence the majority of magnum owners are handloaders.
There’s been a lot of nonsense written about loading big magnum cases with powder charges reduced below what’s normal for the capacity of the case and the bullet weight used. But modern magnums are made from the finest brass for great strength and to give the best results with high pressures.
The excuses for this type of loading are cited as being to bring the big case down the velocity level of a standard case in the same calibre to reduce recoil and make it more pleasant to shoot. Or else, the reloader thinks he’ll get better accuracy from a reduced load.
Neither argument seems logical to me, since if the magnum owner is sensitive to recoil, he’d be better of using a standard cartridge. The only exception being a man who owns only one rifle chambered for a magnum cartridge and wants to do a lot of shooting with it. By loading back slightly, he’ll burn less powder, and reduce throat erosion, recoil and muzzle blast and enjoy shooting his rifle more.
But to load back with the goal of gaining better accuracy is not. In my experience, it would be most unusual for a big case to give better accuracy with reduced powder charges.
Standard cartridges will often produce tighter grouping with slightly reduced loads, but contrary to what many think, the best accuracy with a magnum case generally comes from maximum or near maximum loads; unlike standard cartridges which often give the tightest groups with slightly reduced loads.
In fact, all of my own magnums deliver their best accuracy with loads that are close to maximum. Then there’s the real danger posed by reducing charges of slow burning powders too much, that of experiencing S.E.E (Secondary Explosion Effect) and a blown-up rifle.
The truth is: standard cartridges are far outclassed by magnum cartridges. Good examples of this are the .270 Winchester and the .270 Weatherby.
The standard .270 really needs a 610mm barrel to develop its full ballistics, but most factory rifles have 550mnm barrels which was Jack O’Connor’s preferred length for a mountain rifle.
From the shorter barrel, most .270 Winchester factory loads will drive the 130gn bullet to 2950fps instead of the listed 3060fps, with some loads going as low as 2850fps.
The best handload in my old Ruger M77 with 550mm barrel gave the 130gn bullet 3000fps against 3100 fps in the 610mm barrel of my Carl Gustav rifle. But nothing is carved in stone.
According to my PACT chronograph, 270 Weatherby Magnum factory loads with the same 130gn bullet weight average 3300fps from the 610mm barrel of my F.N Mauser rifle. But with handlloads velocities are boosted to equal those taken in the 650mm barrel of the Mark V Weatherby rifle.
It’s pretty obvious that the .270 Wby’s larger boiler room is going to require heavier charges of slow burning powder.
There’s not much use loading such a high intensity hunting cartridge to anything short of maximum velocity, and there’s a number of propellants that can achieve that purpose.
The champion among them is Reloder 22, a powder intended for high-velocity belted magnums. With Re-22 I was able to get the kind of velocities listed in Weatherby’s catalogue from my 610mm- barreled rifle with all bullet weights up to 160 grains. Accuracy too, was among the best of all powders tested.
AR2213SC and Winchester 785 (discontinued) gave very similar results, with the former having the advantage of efficiency with maximum charge weights almost identical to Re-22.
But when using spherical or ball powders, it is recommended for cartridge-bullet combinations which allow it to be loaded to 90-percent or greater density.
The same comment will apply to Winchester’s new Supreme 780. To date, I haven’t tried Supreme 780 in my .270 Wby, being entirely satisfied with the results I’m getting with Re-22.
When handloading a magnum cartridge, the proper selection of propellants is essential to gaining maximum performance. When loading the heaviest bullets in the .270 Wby, using powders with extremely low expansion ratios, like AR2217 and AR2225, I found that while there was no worthwhile gain in velocity, that recoil increased to an unwanted level. For this reason I decided to stick with Re-22 and AR2213SC.
Out of all the belted magnums I’ve loaded for, I found the .375 H&H to be least fussy about propellants.
My favourite powder for this cartridge with all bullet weights is W-760, but it will produce excellent accuracy and all the velocity I need with powders ranging in burning rate from AR2208 to much slower burning AR2213SC.
Don’t assume that because two cartridges are of like calibre, that the optimum powders for both would be the same.
Take the .458 Win. Mag. and .460 Wby Mag.for example. The .460 has much greater capacity which calls for slow burners like AR2209 and AR2213SC. The .458, on the other hand, thrives when fed faster burning powders like RE-7, AR2206H, and W-748.
When choosing a bullet of conventional cup-and-core construction for magnum cartridges, I believe that it is important to match the bullet to the size of game to be hunted and to prevailing hunting conditions.
Medium weight bullets work fine when shooting deer-sized game at long range, but they often open up too fast for optimum penetration at closer ranges. This especially is the case when the animal is quartering away or toward the shooter, and the bullet must be driven through a thick hide, muscle and heavy bone in order to reach vital organs.
If the hunter knows beforehand that all his shots at deer in a certain area will be beyond 200 metres or so, medium weight bullets of conventional design can be relied upon to get the job done. But he should also be aware that penetration may be lacking at closer distances.
Choosing a premium controlled-expansion bullet is a safer option because it is designed to handle a wide variety of shots at all distances.
This type of bullet will expand when meeting relatively light resistance (such as deer at long range) and yet hold together and retain a high percentage of its original weight to give deep penetration on the largest deer at close range.
Bullets of this type include: Barnes TSX, Nosler AccuBond, Speer Trophy Bonded Bear Claw, Swift A-Frame, Hornady’s GMX and Winchester Power Max Bonded (available only in factory loads).
Thanks to the Barnes all-copper design, the lighter bullets in various calibres will hold together and give deep penetration even at extremely high impact velocities.
Consequently, the hunter who loads Barnes bullets is equipped for shooting big game of various sizes, at both close and long ranges, with a single bullet weight.
Where shots at larger animals may occur at closer ranges, it’s a good idea to choose a heavier bullet such as a 150gn in the .270 Magnum, the 160gn in the 7mm Magnum and 180gn in .300 Magnum.
In fact, I think that bullet selection for magnum cartridges is so critical that developing two loads for a particular rifle is well worthwhile - but only if the rifle is to be used on feral goats and pigs as well as big game. I’ll use my Model 70 in 7mm WSM to illustrate my point.
For hunting smaller deer species, I zero the 150gn Remington Core-Lokt three inches high at 100yds. But for the larger red and sambar stags I change over to the 140gn Barnes TSX with the same powder charge and same zero. The trajectories are not different enough to have to resight the rifle when changing loads.
The “new” Winchester Short Magnum cases require very deep seating of bullets to work through the short magazines of the rifles that are chambered for them. This causes slow burning powders to be heavily compressed which rules out slow burners especially coarse-grained ones.
In my .300 WSM the best two powders have a similar burning rate - Win-760 and AR2209, whereas in my .270 and 7mm WSMs slower powders like Re-19 and Re-22 give equivalent performance. If I had to choose the best propellant for my .325 WSM, however, I’d not go past Win-760.
Magnum primers are necessary to ensure proper ignition with the slow powders used and widely varying ambient temperatures. Standard force primers may work fine with near full-density powder charges at summer temperatures but I’ve found them to be borderline with less than full-density loads (particularly with ball powders), at lower sub-zero temperatures.
I have no preference for one brand of magnum primer, having used CCI 250, Federal 215, Remington 9-1/2M and Winchester Large Rifle Magnum primers without any problems.
When working up loads with belted cases, mike the belt of the case to check head expansion. Measure it before your fire it, then again after firing. Even though the next case may give a slightly different reading before firing, you’ll only know how much expansion it shows after firing by miking it before and after.
If you don’t have a blade micrometer, you’ll have to file a little from the rim on on each side so that it won’t interfere with miking the back of the belt and index the case across the head with a felt tip pen. This technique is described fully in my Practical Reloading Manual.
A softer brand of case will show .001-.0015” expansion of the belt with the first firing of
a factory or full-power handload. Normally, two or three grains of powder can be added to the charge before any further expansion takes place, try increasing the charge one grain at a time and check for further expansion.
If there is none, go up another grain and repeat until the belt starts to expand again. To get a safe working load, back the charge off one grain below the last charge that gave no further expansion.
As a rule belted cases are are limited to four or five full-power reloads. This is due to several factors. Belted cases are supposed to headspace on the belt and handloaders seldom realise that head-to-shoulder length is critical.
Some rifle manufacturers are sloppy about holding chamber dimensions in the area of the shoulder to close tolerances. Often the die maker too is guilty of the same lack of care, and, to make things worse, the handloader is unaware of any of this, so he doesn’t bother to check head-to-shoulder length.
He naturally assumes that the belted case will headspace on the belt and takes no special pains in full length sizing. As a result, when the cartridge is fired, the case shoulder expands forward until it makes contact with the chamber shoulder.
Then, when it is full length sized for reloading, the die pushes the shoulder back again to factory standard length. This process is repeated every the case is reloaded, resulting in weakened and stretched cases; inevitably case head separations occur.
The reloader can get around this by neck-sizing only until cases get hard to chamber, and when full length sizing taking care to adjust the die so that it doesn’t set the shoulder back.
As a big-game hunter, I like magnum cartridges because they give a flatter trajectory and hit harder way out yonder where the game is.
If you have a good rifle and good bullets, they are just as accurate as a standard cartridge of the same calibre.
If you load them down you defeat their purpose. Once you gain enough experience with big magnum cases, you’ll find that they give their best accuracy with near maximum loads.
This article was first published in the June 2014 issue of Sporting Shooter magazine.