Reloading the .257 Weatherby Magnum

The main reason for choosing the .257 Weatherby Magnum cartridge is to obtain more velocity from it than you can get with any standard case of that bore diameter with any bullet in that calibre.

The .257 Wby has a much flatter trajectory over the longest ranges and, delivers more striking energy out where the game is.

The man who appreciates its superior performance most is the trophy hunter who will hunt in country where the shots are long and the game large enough to need the heavier punch.

If the hunter is a good, careful marksman the .257 Wby delivers enough hiting power to take game up to the size of red stag out to a full 500yds.

A misconception believed by some shooters is that the .257 Weatherby is on the same basic case as the .300 Weatherby. Actually, the .257, .270 and 7mm Weatherby Magnums are made by necking down and shortening the .300 case.

The three shorter cases measure 2.545 inches in length as compared with 2.820 inches for the .300 Wby. case. Powder capacity is, of course, much less than that of the .300 case, being a better balance for  the .257 bore.

In fact, there is very little difference in capacity between the .257, .270 and 7mm Weatherby cases and the  .264 Winchester and 7mm Remington Magnum cases.

The .257 Wby towers over all of the other .25 calibre cartridges factory and wildcat and uses larger powder charges to outperform them all by a wide margin.

In the past the .257 Wby was often criticized for being badly overbore capacity and relatively inefficient, as well as being extremely hard on barrels. But with today’s ultra-slow burning propellants it can no longer be called “overbored” although, like all the other smallbore large capacity magnum cartridges barrel life is undeniably somewhat limited.

If I could find anything to criticise about Weatherby’s quarter-inch hotshot, it is that despite having a double-radius shoulder, cases do have a tendency to stretch and grow in length when subjected to full-power loads.

New cases measure 2.540”, but if maximum working loads are used, their necks can stretch after two or three reloads to exceed the 2.549” recommended maximum. When developing loads for a new rifle, I’ve found it necessary to trim cases back to 2.540” after as few as three firings.

Once fired cases (including fired primers) have an average weight of 211 grains and internal capacity of 83.5 grains of water. The .257 Wby uses larger powder charges than similar .257 wildcats on the .300 H&H case, a category which includes the .250 Durham Magnum, the .250 Bennett Magnum, the .25 Ackley and .257 Critser Magnums, and the newer .25 WSM with the same bullet weights.

This is due not entirely due to case capacity, but to free-bore throating in Weatherby rifles. The free bullet travel before the engraving process of the lands starts drops initial resistance and pressures, thus allowing more powder to be used to build up the same pressures as given by the other .25 magnums. This results in a slight velocity increase if pressures are the same when using the same powder, charge and bullet.

Originally, Weatherby .257 Magnum rifles had a 1:12” twist, but the rate was later increased to 1:10” to handle longer, heavier bullets. The older Weatherby rifles also had 3/4-inch of freebore, but the throating of all Weatherby rifles was changed in 1967 – 1968 to about 3/8-inch. That is, all except the .240, which has always had a throat of conventional length.

With the long magazine of the Mark V action, it is possible to seat all standard .257 bullets with their bases flush with the base of the neck. This gives a bit less free-travel than would be the case using reloads with the heavier bullets seated out beyond factory overall case length.

With bullets of 100 grains or less, bases were seated to a depth of one bullet diameter. The 100gn spire-point bullet used in the standard Weatherby factory load appears to be from Hornady, and has the crimping cannelure located so that the base of the bullet is flush with the base of the neck.

There’s enough room in the magazine to seat the 100gn Hornady out farther; with a seating depth of about one bullet diameter it protrudes considerably beyond the mouth of the case.

With the seating depths used in testing, case capacity was increased slightly while free-travel was reduced, so the gain in powder capacity is probably offset by the reduced free-bore effect. It is, however, doubtful that pressure and velocity would be affected much.

No factory ammo or unprimed brass was available to accompany the rifle, but I found a box of 100gn loads in my reloading room which got me out of trouble.

Most reloading manuals show maximum charges giving velocities a bit lower than Weatherby’s published factory load velocities. My load development work was made easy since all I had to do was duplicate Ray Smith’s time proven data. None of the loads listed in the load table gave excessive pressure in the test rifle, as all were checked 1 to 2 grains higher.

The loads were put out in once-fired cases and belt expansion held to about the same level of expansion as given by factory ammunition.

It is possible to obtain more velocity, for all charges listed could be increased by at least two grains without the bolt showing sticky lift, but such charges expanded primer pockets if fired repeatedly in the same case.

They would be perfectly safe under normal hunting conditions in new cases or even if the same case were used two or three times, but primers would be loose after that, rendering the cases unusable.

The loads settled on will give long case life, as many of the cases were fired up to eight times with the listed loads. They also give trouble-free hunting reliability under all weather conditions in the test Mark V rifle. They are not recommended for use in any other rifle without working up from at least 3 grains below.

In dealing with belted cases, I always mike the belt of the case to check head expansion. Don’t waste your time miking the rim. Few cases have rims that are concentric enough to mike properly – they have burrs, flat spots and nicks.

Furthermore, every time a case is extracted it may come up with another rough spot. Few cases are perfectly round even on the belt, and they are not all the same size – I’ve found they can vary as much as  .001” in one box of unfired brass.

Check each individual case before you fire it, then after firing. Even though the next case may five a slightly different reading before firing, you will know if it shows expansion after firing only by miking that case before and after.

If you have an standard micrometer, index the case across the head and file a little from the rim on each side so it will not interfere with miking the back of belt just forward of the extractor groove. If you have a blade micrometer, this will not be necessary.

Some of the cases with softer brass will show .001-.0015” expansion of the belt with the first firing of a factory load (or full-power handload). If the case is reloaded with a charge that duplicates the factory load, it’s almost certain that no further expansion will take place.

As a rule, the charge can be increased by another two to three grains of powder before further expansion will take place. Try adding another grain of powder and repeat until the belt starts to expand again.

When this happens back the charge off one grain below that last charge that gave no further expansion and you have a safe full- power working load for the .257 Wby in that particular rifle.

Don’t keep increasing the charge until the bolt becomes hard to open with this big case, since it doesn’t happen soon enough to be a true indicator of too-high pressure. Often with this big, straight-sided case it’s not unusual to blow a primer before the bolt gets sticky.

Weatherby cases are made from the finest brass, and are designed with great strength to safely handle high pressures. When working at such high pressures and neck-sized only, a case can seldom be reloaded more than two or three times before the body does not spring back enough to enter the chamber without having force applied.

To eliminate this problem the case will have to be resized, however, it’s just as easy to full-length resize on every firing to ensure reliable functioning. But cases should be resized only enough to allow them to chamber with a slight feel, and care taken to make sure that the sizer die does not set case shoulders back, or even contact case shoulders, otherwise case separations may occur.

One point I’ll emphasise is the importance of maintaining the correct head-to-shoulder distance for proper headspacing. Even  though the belted case is supposed to be headspaced from the face of the bolt to the forward edge of the belt, some manufacturer’s chambers are pretty sloppy in this dimension. However, in all the Weatherby rifles I’ve played with head-to-shoulder fit in the chamber has been tight.

As far as accuracy and bullet weight are concerned, I’ve found very little difference between the bullets used from the 120gn Hornady down to the 100gn Speer.

It seems logical that some other makes of bullets in the same weights might give either better or worse accuracy. Also, juggling the powder charge would likely tighten groups in some instances.

It is difficult for me to consider the .257 Wby Magnum as a combination big game-varmint cartridge, but with light bullets in the 90-100gn bracket it is capable of doing a good job on predators at long range.

Both the Nosler 100gn Partition and 110gn AccuBond gave excellent accuracy with their best loads, and if load development were carried to the finest point for these bullets excellent long range performance would be assured on all classes of varmint-predators.

The Barnes 80gn TTSX can be driven at a sizzling 3870fps in a 650mm barrel. With a 300yd. zero it drops only 17.4 inches at 500yds, making it the flattest shooting of all the Weatherby cartridges at that distance.

At 500yds, velocity is still 2514 fps, again the highest-impact velocity of any Weatherby factory load, including the .300 and .30-378 Weatherby Magnums. Energy at this distance is 1123 ft/lb which is considered adequate for deer.

The best accuracy in Ray Smith’s Mark V and my test Ultra Lightweight was obtained with the Hornady 117gn SST and Nosler 100gn Solid Base BT and 115gn AccuBond.

While some of the bullets with conventional style jackets will do a reasonably good job on quite heavy game in 120gn weight in the.25-06, the are almost certain to break apart from fired from the .257 Wby. For that cartridge heavy controlled expansion bullets are a must, and there are a number of fine “deer” bullets in .257 calibre.

When loaded with strongly constructed designs such as the Barnes Triple Shock, Swift A-Frame, Hornady GMX and Nosler AccuBond, the .257 Wby is capable of cleanly taking most deer species up to the size of sambar and wapiti and most African plains game.

By carefully tailoring handloads, the hunter can obtain outstanding accuracy with the .257 Wby and its mild recoil allows hunters to shoot it accurately and place their bullets far more precisely than they could with a heavier-recoiling cartridge.

It may be well to add a warning for varmint hunters who aspire to use the .257 Wby. First barrels heat up extremely fast. Firing three shots in normal accuracy test work, will make the barrel very hot, and five at the same rate of fire makes the barrel too hot to hold – unless you have a hide like a politician. If too much varmint shooting were done on a hot day, it would be possible to burn the throat out in a single afternoon.

Over the years Ray Smith has tried many powders in several rifles chambered to .257 Wby Magnum, and when it comes to squeezing maximum velocity from the cartridge, Alliant Reloder 22 and 25 became his preferred propellants.

Only with those two powders was he able to consistently equal the velocity of Weatherby’s factory loads at acceptable chamber pressures.

Having such a large boiler room and small diameter bore, the  .257 Wby thrives on slow burning powders such as AR2209, AR2213sc and Re-19, to squeeze the highest velocities with bullets weighing up to 90 grains.

With heavier bullets, Re-22, Viht-N 165, AR2217 and Re-25 deliver the highest velocities. But even then unless heavy charges of those powders are burned, a lot of loads produce bullet speeds no faster than the .25-06.

The  .257 Wby burns up to 80 grains of ultra-slow powders but extended shooting of that much powder is hard on a barrel. Average charges run from 65.5gn to 68gn with slow Re-22 and Re-25 and the most useful bullet weights – from 100 to 117 grains.

It is amazing how, burning such heavy charges of slow powder, the .257 Wby produces such low velocity spreads. Alliant Re-22 went as low as 5 to 16 fps; and Re-25 4 to 12 fps accompanied by tight grouping.

This is why Ray Smith settled on Re-22 and Re-25 as being the best propellants for the big quarter-bore. Federal 215 Magnum primers were used for all loads as we found long ago that they gave the most consistent ignition.

The way I sum it up: if you like the .257 bore and yearn for a magnum cartridge, the .257 Wby is the best choice as it will take care of most Australian hunting quite well. That performance comes at a price, in terms of the extra cost of brass and powder, but it’s well worth the expenditure. 

This article was first published in the September 2014 issue of Sporting Shooter magazine.





Like it? Share with your friends!

What's Your Reaction?

super super
fail fail
fun fun
bad bad
hate hate
lol lol
love love
omg omg
Nick Harvey

The late Nick Harvey (1931-2024) was one of the world's most experienced and knowledgeable gun writers, a true legend of the business. He wrote about firearms and hunting for about 70 years, published many books and uncounted articles, and travelled the world to hunt and shoot. His reloading manuals are highly sought after, and his knowledge of the subject was unmatched. He was Sporting Shooter's Technical Editor for almost 50 years. His work lives on here as part of his legacy to us all.