.257 Weatherby handloading assessment

A long time ago, when I was involved with auto racing, I found that a pencil and paper and a little basic math could save tremendous amounts of time and money. Why try an endless stream of carburetors,  tire sizes or gear ratios, when simple calculations could get you to a workable combination ? In some ways, properties of firearms are very much the same.

A pocket calculator and a handful of ballistics formulas, or one of the many decent ballistic software products on the market, can pretty much predict what performance to expect out of a cartridge / firearm combination. Whenever I think I’ve found a cartridge of interest, I tend to look through all of the load data and external ballistics I can find or, if there isn’t enough data to analyze, I’ll use one or two software programs to model the cartridge and project interior and exterior ballistics. From playing around with these models, I’ve also developed a better understanding of what I look for in cartridge performance.

A flat shooting, hard hitting cartridge that is loaded to its potential can push a bullet with a sectional density above .280, at a velocity above 3,000 fps. There should be bullet selections for the cartridge with a ballistic coefficient greater than .450. With this criteria met, regardless the cartridge selected, I can zero somewhere between 230 and 240 yards, and be point blank on a 6″ target out to 300 yards. Feel free to write to highlight how many points I’ve missed. The .257 WM actually came in with a less than optimal bullet weight selection, but made up for the difference with additional velocity. I assume the .257 bore has been traditionally looked at as acceptable for smaller game, and there were not enough cartridges performing at .257 WM velocities to drive the production of heavier bullets. 

At a time when 80 grain .224 bore and 240 grain .308 bore and 300 grain .338 bore bullets offer increased sectional density and ballistic coefficients for long range shooting, the .257 bore does not have a comparable bullet.

SD = W/D²  SD=Sectional density, W=bullet weight in lbs, D=diameter squared.

A 117 grain .257 bore bullet has an SD of .250, 120 grain bullets have an SD of .263. A 130 grain .257 would have an SD of .281. It would take a 170 grain .257 bore bullet at .367 SD to match the long distance bullet weights available for the .308 and .338 bores. Of course a heavy weight bullet would increase bullet length, which in turn would require a different rifling twist. As an example, the 240 grain .308 bullets require a 9″ twist. The .257 Weatherby has a 10″ twist that would have to be changed to about an 8″ twist to accommodate a 170 grain bullet. Preliminary calc’s suggest I couldn’t hit the 3,000 fps mark with a 170 grain bullet while remaining within livable chamber pressures, but I could hit 3,100 fps with a 160 grain bullet. There would be a 700 – 800 ft/lb muzzle energy pick up over a 117 grain bullet, that would hold the .257 to over a ton of energy out past 350 yards. Pretty good for a small cartridge in a small rifle.

One of the reasons I selected the .257 WM was the near future opportunity to explore custom bullet making for perhaps heavier than typical weights. I also thought there was a solid potential to develop some meaningful improvements in load data, based upon the preponderance of old data that appears in even newly released loading manuals. Like many high intensity cartridges that have been on the market for an extended period of time, bullets and powder have begun to catch up with cartridge potential, so there are significant gains to be had with some minor experimentation. It was interesting to note, within popular hunting bullet selections, the .257 WM and .30-378 have the same powder capacity to bullet weight ratio of .66 grains of capacity to each grain of bullet weight. Maybe there is a clue in there someplace.

The cost of handloading for a new cartridge

Every time a cartridge is added to the handloading list, there are some basic materials that need to be purchased, or are hopefully already in place for use with another cartridge –

• Reloading dies

• Neck reamer pilot

• Shell holders for APS priming, trimming and Rock Chucker press

• Shell plate for the Ammo Master press

• Selection of bullets

• Primers

• Selection of powder

The RCBS #4 shell holder and shell plate, trimmer holder were already in place for use with my 7mm Remington Mag. The neck reamer pilot is the same as used for my .25-06. The set of full length sizing dies cost about $40. The value of the accessories I already had in place came to about $60.

Initial bullet selection

I wanted to try a variety of bullet weights, types and coatings, even if only to verify assumptions made on bullet weight and accuracy, as well as velocity potential. Rifling recommendations for some of these bullets are significantly different than the 10″ twist Weatherby spec. I won’t know what the optimal rate is for each bullet until I have them in hand and can measure the actual bullet, but manufacturers suggested rates from 15″ to 10″, where nothing under 117 grains was as quick as 10″. Early versions of Weatherby’s .257 had a reputation for poor accuracy. This was reportedly caused when Weatherby, assuming shooters would load the rifle with light bullets, used a slower twist that would not properly stabilize heavy bullets. Eventually, the rate from the factory was modified to accommodate heavier bullets, but I don’t know how much light bullet accuracy was compromised.

Why is there a 75 grain bullet in the mix ? Actually, there is also a totally inappropriate 60 grain bullet I selected, but didn’t put in the table. One of my goals was to get something out of the barrel in excess of 4,000 fps. 

Powder Selection

In thumbing through the manuals, it seems there is only one powder slow enough to fill the case, H870. All the rest of the powders recommended are relatively fast, resulting in 75% capacity loads. Accuracy usually comes with a near full case, but most of the maximum loads listed utilized IMR 4831. There were a couple of listings that looked more promising with recommendations for at least RL22 and IMR 7828. The Nosler #4 guide was a little odd in that it listed a light bullet load with 7828, and heaver bullets topped out with 4831. Usually 7828 works best with heavy bullets and powder charges. The current Speer manual listed 7828 loads for the .25-06 with it’s lesser case capacity, yet offered no 7828 loads or the .257 WM. I suspect, as an older proprietary cartridge, handload manual publishers just haven’t taken the time to revisit the .257 WM. 

I will probably focus powder selections on IMR 4831 & 7828, Reloder 22 & 25, and H870. Hopefully I’ll be able to try Norma MRP, their site lists some exceptional 117 grain results. I thought I’d try Vihtavuori, a powder brand I rarely use. However, they offered no data for the .257 WM and loads listed for cartridges like the .264 Win mag and 7mm mag were less than impressive; I just didn’t see the opportunity to experiment.

Summary

This brings me to where I am, everything on order and in transit. I have several boxes of factory ammo to test and record data for comparison, and to use as a source for brass. The .257 is an expensive little bugger to shoot without handloading. Bullets, powder and primers are inexpensive, but brass is a little steep, as is loaded ammo. Hopefully, I’ll be back shortly with some tangible handloading results.

  More “The .257 Weatherby Ultra Lightweight”:
Pick up Day for the .257 Weatherby Ultra Lightweight
Scope selection for the .257 Weatherby project
.257 Weatherby handloading assessment
The Weatherby Mark V .257 WM at the range
Reloading the .257 WM …in excruciating detail Part I
Reloading the .257 WM …in excruciating detail Part II
Handload Data 257 Weatherby Magnum

Thanks,
Joe