Target Sports

HANDLOADING: SHORT AND STOUT

Created on 14th May 2009

In part one of a new series, LAURIE HOLLAND looks at the construction of the Winchester Super-Short Magnums and their performance when handloaded

ONE OF the more interesting, if controversial, cartridges to appear in recent years is the Winchester Super-Short Magnum or WSSM, this short, fat number using a common case in .223, .243 and .25 calibres. It was developed from Winchester's WSM in 2001. This in its .300 form quickly became the most commercially successful American sporting cartridge introduction since the 1960s 7mm Remington Magnum, or in Winchester's case its even older .243 and .308 WCF numbers. With the US market apparently enamoured of this design in four calibres from .270 to 8mm, Winchester's boardroom thinking presumably ran along the lines of: why not adapt it to smaller calibres, to increase already healthy sales further?

While .223 and .243WSSM rifles are regularly advertised by our dealers, I cannot remember seeing a .25 for sale - I'm sure there will be some around, but it must be a very small number. I managed to get hold of rifles in the two smaller calibres, letting me have a go at handloading these pocket rockets. Irrespective of whether using them turns out to be a satisfying exercise, shooting a WSSM is good for firing point one-upmanship as nearly everybody wants to know what it is, examine it, and ask how it performs.

Design issues

There was no question of Winchester simply necking the parent WSM case down - it had far too much capacity so would be very inefficient in small calibre form. Its 2.100" long case was shortened by a little under half an inch to 1.67", reducing internal capacity by almost a third. Case body length (and neck diameter) aside, there was only one other change: the WSM's fairly sharp 35º shoulder angle was reduced to 28º to improve feed from the magazine and/or simplify case manufacture. The result is the largest body diameter to case-length ratio of any factory cartridge, the former a huge 0.555" inherited alongside the rebated case-head form from the old British .404 Jefferey elephant cartridge via the WSM. WSSM overall cartridge length (COAL) is also short, with all three versions listed at 2.360", nearly half an inch less than .308 Winchester and its .243W offspring. In practice, factory rounds are loaded to a still shorter COAL comparable to that of the little .223 Remington. Another feature is the use of minimal body taper. Fired Winchester .243WSSM cases from my Winchester 70 Stealth measured 0.556" just above the extractor groove, reducing to 0.548" at the body-shoulder junction, a mere eight thou reduction compared to 14 thou in fired Norma .243WCF (.243 Winchester) cases, and a very much larger taper still in .22-250 Remington cases. (Resizing .243WSSM cases increased the amount of taper to 11 thou while .243WCF kept the ratio more or less the same, lower case body and shoulder diameters reduced by a near identical amount.) It's not a simple matter of this being the norm for short, fat case designs either, as still shorter but smaller diameter Lapua 6BR cases exhibited 12 thou difference in diameter at these points when measured straight out of the manufacturer's carton.

Capacity

These diminutive cartridges seem turbocharged given the MVs they produce, but the super-fat body actually gives their cases more capacity than you might imagine. The standard way of identifying such is to weigh a fired, unsized case with the spent primer in situ, then repeat the exercise with it filled up to the case-mouth with water, the difference being ‘water capacity'. This can be converted to a volumetric measure such as CCs, but water capacity is the standard measure. (I'll stress that we're talking about the weight of water here not powder charges.) The reason for using a fired rather than new or resized case is to identify the effective capacity in your rifle's chamber. There is a noticeable and potentially significant pressure difference, for instance, between cartridges fired in a minimum dimension match chamber and those used in a maximum tolerance mass-produced equivalent.

Fired .223WSSM cases held 54.3gn of water and .243WSSMs were marginally larger at 55.6gn. This was no doubt due to the larger diameter neck, the actual combustion chamber space being identical or near enough as to make no difference. How does this compare to competitors? Taking the smaller calibre first, Winchester .223 Rem cases come out at 31.5gn and PMC .22-250 Rem cases 45.3gn. The nearest competitor to .223WSSM is the .220 Swift (another Winchester design, but introduced nearly 70 years earlier and no longer produced by that company). I don't have any Swift cases to hand, but QuickLOAD lists its capacity as 47.0gn water, so it'll be somewhere around that level. Moving onto .243, my fired WSSM cases ran at 55.6gn against 55.9gn for Norma .243WCF (.243 Winchester) examples. Norma usually produces the thinnest walled cases around, hence with the greatest internal capacity, and some Winchester .243 cases I'd previously measured held around half a grain less than the WSSM.

What this means in practical terms is that the .223WSSM case has around 70%, 20%, and 15% more capacity than the .223 Rem, .22-250 Rem and .220 Swift respectively, but the .243WSSM has no apparent advantage over the half-century old .243WCF. In fact as we'll see, it has a slightly smaller effective powder capacity than the common or garden two-four-three once we get into bullet seating depths. We can easily see how the .223 Wuzzim produces more performance than the smaller designs, but how does Winchester manage it with the .243WSSM? (Or does it actually manage this trick, as there may be a discrepancy between reputation and actual performance?) And what benefits, if any, can we reasonably expect from the ‘modern' short, fat case shape?

Pressure and performance

The Swift is not a common number, but .223s and .22-250s are ten-a-penny, so do we have a cartridge in the .223WSSM that is going to improve on their MVs by huge amounts given these increases in case capacity? Er, not quite. A rule of thumb is to divide any such case capacity percentage increase by four to identify a realistic MV improvement, so the .223WSSM should give us velocity increases of about 17.5% over .223 Rem and only 5% over .22-250 Rem with the same weight bullets. Look at factory cartridge ballistics, and that's pretty well what you get (table one). However, the .243 calibre version manages to produce another 130-150fps with the 95gn Ballistic Silver Tip (BST) bullet over equivalent loads in its similar capacity .243WCF and 6mm Remington rivals. This MV increase is nearly 5%, equivalent if all other things were equal to using a 20% larger case, so why this result? Despite what many people think, this has little or nothing to do with the super-efficient short fat case producing more power from the same weight of propellant due to improved combustion. Rather, the BST is a low-friction coated bullet and the charge is increased to take advantage of this feature. Then there is pressure - the WSSM is allowed another 5,000psi over its older WCF sibling, and it's obvious that the factory uses up every one of those pounds to achieve commercially vital high MVs. The 6mm Remington is another 65,000psi cartridge, but I suspect Hornady keeps pressures down in the sole factory 95gn load in this nearly obsolete cartridge, as it easily outperformed its Winchester rival when the pair were fighting it out for sales to American hunters 50 years ago. Note, however, that the Wuzzim gives virtually no benefit over .243WCF with 100gn bullets and is well behind the Hornady ‘Light-Magnum' 6mm Rem load.

Actually there is one internal ballistics advantage that very short designs have over equivalent traditional competitors - they increase the length of the barrel. Pardon? Barrel length is measured from the muzzle to the bolt face and therefore includes the chamber, so the working (rifled, less than bullet diameter) bit of a nominally 24" tube is that length minus the chamber and throat up to the point where the leade grips the bullet, just under 2.6" in a new .243WCF rifle with no throat erosion. It's around 2.1-2.2" in a rifle chambered for our stubby .243WSSM, so there is an extra 0.4-0.5" of working barrel, worth maybe 30-50fps depending on bullet weight in this size of cartridge, all other things being equal.

Model T

Adapting Henry Ford's statement to the Model T's choice of colours, you can have any make of WSSM case you like provided it's Winchester. Actually, you can have two colours, with factory Supreme grade ammunition coming with a shiny silver finish care of nickel plating, and other grades displaying plain brass. Since you couldn't get unprimed/unloaded brass when I first tried the .243 version, I have 40 plated examples having started with some boxes of expensive factory ammo in standard and Supreme grades. I'm not a fan of nickel-plated cases, though. My admittedly limited experience of the genre in three different cartridges suggests they have much increased neck-pull (case grip on the bullet), and (probably related) are more prone to splitting prematurely, or maybe I've just been unlucky. You can now buy 50 packs of (unplated) .223 and .243 types, letting you handload either Wuzzim for a third of the price of factory fodder.

Let's look at these cases. We've already noted the .243 version has the same capacity as the long-established .243WCF, but is a half-inch shorter. You might therefore expect the two cases to have similar weights, or if there is any difference, for the WSSM form to be lighter given the short case. Not so - Norma .243s averaged 166.4gn including spent primers, while the WSSMs came out at 212.2gn - a 27.5% increase. Where do these vertically-challenged but obese cases get the extra grains from? In two words, massive construction. Look through the flash-hole of a shiny new case while angling it and you'll see a massively thick case-web; measure case-neck thickness and both calibres run from 0.020 to 0.022". That compares to 0.015-17" for .243WCF brass, and 0.011-14" for .223 Winchester necks depending on make.

Consistency

Bear in mind that benchresters turn their 6PPC necks down to 0.0085 (eight and a half thou) because thin necks give lighter, more consistent bullet-pull with the proviso that the appropriate bit of the barrel chamber is machined with a diameter only marginally above that of a loaded round. WSSM neck uniformity actually wasn't too bad for mass-produced US cases, with a two thou range across the whole sample, rarely more than one thou variation around any individual case's neck. Case weight uniformity was another matter entirely. A random sample of 10 .223 examples ranging from 207.1 to 215.2gn saw an 8.1gn variation overall, or an unacceptable 2% either side of the median weight. Ten 243s covered 210.7 to 216gn, only slightly better. The .223s had a wide spread, but most .243s were consistent, weighing in the 211s and 212s, the large variations coming from a minority that were much lighter or heavier than the norm by around three grains. What does this do to accuracy? A five-grain range, never mind eight-grain range, will produce different pressures and combustion behaviours, likely caused by large wall thickness variations between cases. This will in turn produce combustion chamber volume variations, so it's not good news.

The super-heavy construction is presumably dictated by the 65,000psi maximum pressure, possibly aggravated by the manufacturer being concerned at the likelihood of many users handloading these high-performance numbers beyond this ceiling. There is another possible reason in that, as we'll see next month, this design has a tendency to produce unexpected pressure spikes with small charge increases/variations that could well see a weaker case leak gas from the primer pocket or even fail completely. Given this decidedly undesirable tendency, large case weight (hence internal capacity) variations will aggravate the problem. I may have experienced one such example with 19 rounds in a test batch displaying low pressure, but the 20th forcing the case head back into the extractor slot on the bolt-face in a big way - a not-to-be-ignored over-pressure symptom. (This was with individually weighed charges, and the problem example didn't use the top load either.)

Any other case gripes? Yes, I'm afraid so. Three .223WSSM cases out of 100 new examples were rejected because of neck folds. With these cases priced at 53.5p each that was £1.60 gone west. With the huge degree of case-forming from a 0.555" diameter body down to less than half that in the neck, one can understand manufacturing difficulties, but frankly, 3% of cases being so obviously faulty suggests lamentable inspection standards. The .243s didn't suffer from this problem, probably due to the reduced amount of brass-forming in their manufacture. However, one starts to consider other manufacturing practices and quality control issues with this design, in particular neck and shoulder annealing given the degree of metal mangling required to produce the short, fat shape. I lost a few in both calibres to neck or shoulder splits after only three or four firings, despite both rifles being commendably well-dimensioned in the chamber neck area, over-slack chambers being a common cause of such failures.

The super-thick brass produced another potentially undesirable feature, but fortunately one that was easily rectified. With the case-head being so thick, the little brass spikes that usually form around the flash-hole edges inside the case in punched-through examples like these (as opposed to Lapua, Norma and RWS who drill the holes) are of an unusually large size. These could be seen clearly by looking through the flash-hole of a new, shiny-clean case. These shards affect powder combustion uniformity randomly, but are easily removed with a couple of twists of a flash-hole reamer. Their size and thickness was soon apparent however, my Lyman tool needing far more effort than usual, and some cases producing a surprisingly large pile of brass chips.

Cartridge lengths

The WSSM COAL is set at 2.360", and the two .243WSSM factory loads (55 and 100gn) I tried were loaded around a tenth of an inch shorter. When I reloaded cases from these rounds, I still didn't have a modified case for my Stoney-Point/Hornady L-N-L OAL gauge, so had to ascertain suitable bullet seating settings by traditional methods. In this case I seated an 87gn Hornady HPBT bullet to the SAAMI-specified 2.360" COAL to see if there was any resistance on chambering the cartridge. There was, in fact the bullet was jammed so hard into the rifling I couldn't close the bolt. So, measurement is vital as Winchester rifles at any rate are short-throated.

Of the various bullets subsequently measured using the OAL Gauge, only one - Lapua's 90gn Scenar match - reached or exceeded the standard 2.360", most being in the 2.22 to 2.275" range when set just off the rifling. This is no real matter with the lightest bullets, short 55gn jobs, but becomes more significant as the bullet's weight and hence length increases. Subtract the 1.67" WSSM case length from the 2.275" COAL required by Sierra's 0.243" 100gn flat-base Spitzer No. 1540 in my rifle and you have 0.6" of the bullet exposed. With this bullet measuring 1.035-1.045", there is some 0.445" of its body down inside the case, and you can add another 0.1" or more for boat-tailed versions of this bullet weight. With the WSSM case-neck under 0.28" long, heavy bullets have their shanks intruding far into the shoulder area. This is significant as many recommended loads use case-filling, even compressed charges of slow-burning powders.

Knowing that many makes of .243WCF case have a near-identical internal capacity to the WSSM, I asked QuickLOAD to calculate usable case capacities for both designs when loaded with the 100gn Sierra boat-tail at 2.71" for the .243WCF and 2.275" for the Wuzzim. The result was 53.215gn (water) for the older cartridge and 52.04gn for the WSSM, so the latter has a marginally (2%) reduced combustion chamber volume and holds slightly less powder, with heavy bullets at any rate. This is not an issue with the lighter 0.243" varmint bullets or the 40 to 63gn types normally loaded in the .223 version.

Next month, I'll move onto loads data and sources, bullets, tools and the loads tried with their results which were sometimes good, but not so great in many combinations. Having managed to actually chronograph most combinations despite a miserable, wet summer I'll also answer the question as to whether this pair of WSSMs really produce the super-high MVs claimed for the design.