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GUNS Magazine October 2010 - Page 22
• JOHN BARSNESS • And some new powders for loading same. t’s been a decade since the Winchester Short Magnums (WSMs) I and Remington Short Action Ultra Magnums (SAUMs) showed up to beguile the average shooter into tossing aside his old 20thcentury magnum. There were three main advantages claimed for these short, fat, beltless (SFBL) magnums, according to the advertising hype. The new rounds burned powder more “efficiently,” due to their short cases, so the same ballistics could be achieved with less powder, resulting in lighter recoil. The SFBLs were also more accurate, since the powder burned more consistently. Because they fit in shorter actions, hunters could easily climb higher mountains and stalk thicker cover, because the rifles would be lighter and handier. As with most advertising, these claims turned out to be “not exactly.” When ammunition is tested for pressure, more than just average pressure enters into the equation. The pressure of individual rounds also isn’t allowed to rise over a certain level. The SFBLs do burn powder more no replacement for displacement.” The same principle applies to rifle cartridges: More powder room is the only way to get more speed at equal pressures. This also relates to the real reason some people believe rifles chambered for the SFBL’s recoil less than larger belted magnums: Their ballistics don’t quite match those of larger cartridges. Plus, if by some chance the muzzle velocity of an SFBL is the same as that of a belted cartridge, recoil is indistinguishable. This is basic Newtonian physics. But the SFBLs do burn powder more consistently than longer cases, so do indeed have more potential for accuracy. Bob Nosler tells me the Nosler ballistic lab used to use the .308 Winchester for accuracy testing of lighter .30 caliber bullets, and either the .30-06 or .300 Winchester Magnum for testing heavier .30-caliber bullets. These days Nosler just uses the .300 WSM for all their accuracy testing. However, that’s with a heavy, topgrade barrel, shooting on an indoor range. In factory-made hunting rifles any accuracy advantage is more elusive. My .300 WSM is a newer FN-made Winchester Model 70, a 2008 Limited Edition with fancy wood. It is very accurate, but no more accurate than my .300 Winchester Magnum, a Heym SR-21. Similarly, my 7mm SAUM, a stainless/synthetic Remington 700 BDL, is also very accurate, but still doesn’t shoot any better than a synthetic 700 ADL in 7mm Remington Magnum I owned a few years ago. The 7mm SAUM, by the way, gets just about exactly the same ballistics as the .280 Remington Ackley Improved, because the 7mm SAUM and .280 Ackley have just about exactly the same powder capacity. As for the shorter, lighter rifle advantage of the SFBLs, the average “short” action, whether a Remington 700 or Winchester Model 70, is less than an inch shorter and only 3 or 4 ounces lighter than a long action of the same make. This is why both of my SFBL rifles weigh more than 8 pounds scoped and, with their 24" barrels, are just slightly shorter than a “normal” rifle. In the real world this makes no difference at all. THE TRUTH ABoUT SHoRT MAGnUMS consistently, and this does allow the average pressure of their ammunition to be a little higher than with those old-fashioned belted magnums. The consistent pressure of SFBL rounds allow the level of the safe average pressure to be a little higher. For instance, the average pressure allowed by SAAMI for the .300 WSM is 65,000 psi, while the average pressure allowed for the .300 Winchester Magnum is 64,000. That may not sound like much, and it isn’t. It’s also the reason the .300 WSM, contrary to advertising hype, can’t match .300 Winchester Magnum ballistics, because the .300 Winchester has more powder capacity. As somebody once said in regard to gasoline engines, “there’s theoretically,rifleschamberedfortheshort,fat,beltlessmagnumsarelighterandkicklessthan “normal”magnumrifles(above),but,inreality,thedifferenceissotinyitdoesn’texist.thetwo testrifles(below)areanFN-madeWinchesterModel70in.300WSMandaRemingtonModel700 BDLin7mmSauM. 22 WWW.GUNSMAGAZINE.COM • OCTOBER 2010