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GUNS Magazine March 2010 - Page 22
HANDLOADING • John Barsness • BULLET SEATING DEPTH On both ends. ost handloaders have heard more than one “rule” about rifle M bullet seating. One is rifle bullets need to be seated close to the rifling for the finest accuracy. The standard advice is .03", or around 1/32". Not bad advice, but First, we must understand the reason for seating the bullet so close to the lands. It’s simple, really: The bullet should enter the rifling aligned with the bore. If the bullet is tipped slightly it enters the rifling at a slight angle, and exits the muzzle at a slight angle. This cockeyed bullet takes longer to settle down after leaving the muzzle, and also is slightly deformed. Neither helps accuracy. Seating the bullet out until it almost touches the rifling theoretically helps prevent the bullet from tipping before it’s shoved into the lands. However, obvious exceptions exist, including the free-bore (long throat) in Weatherby rifles. In any Weatherbymade rifle chambered for a Weatherby cartridge, there’s no way to seat the bullets out near the lands and have the cartridge fit in the magazine, yet today’s Weatherbys shoot remarkably well. There are three in our house, a Mark V Ultra Lightweight and two Vanguards, chambered for the .240, .257 and .300 Weatherby Magnums. All shoot very well, because the freebore is just large enough to allow the passage of a 6mm, 25- or 30-caliber bullet. This “tight” throat doesn’t allow the bullet any room to tip slightly, even though it makes a relatively long journey before encountering the lands. Another good example is my CZ 550 in 9.3x62mm Mauser. Even though the magazine allows a cartridge overall length of 3.48", the throat is so long no bullet I’ve yet tried can be seated anywhere near the lands. Yet this rifle consistently shoots about any bullet into much less than an inch at 100 yards. The reason, again, is a throat just over bullet diameter. Also, some bullets will shoot more accurately (or at least as well) when seated farther from the lands. In my experience both long-shanked and relatively “hard” bullets can be seated well back from the lands, especially in a throat of the proper diameter. The most accurate loads I’ve found in those three 22 case holds about 75 grains of water with a 180 seated. A little math shows us that the extra 1/10" decreases case capacity about 2.5 percent. Wow! it isn’t the whole story. A little research into various loading manuals shows when a 200-grain Weatherby rifles have all featured either bullet is loaded in a .300 WSM case, monolithic bullets such as the Barnes the powder charge has to be reduced Triple-Shock X-Bullet and Nosler about 2.5 percent. This isn’t because the E-Tip, or heavier lead-cored bullets with longer bullet takes up more room, but long shanks, whether heavy Hornady because a 200-grain bullet creates more Interlocks, Nosler Partitions or Sierra pressure than a 180. So the “loss” in GameKings. case capacity doesn’t mean a thing, the Softer bullets, especially in lighter reason a 200-grain bullet works just fine weights, can vary considerably in their in the .300 WSM. reaction to seating depth. One of the In fact, if we do a little more math softest bullets on the we find out a 200-grain market is the Berger Partition sticks way VLD. Often these down below the neck shoot best when of long 30-caliber actually touching the magnums. If seated to lands, but in some normal overall cartridge rifles they prefer length a 200-grain considerable jump. bullet extends just as far In fact, some below the neck in a .300 experimentation in Weatherby Magnum seating depth often as it does in the .300 results in better WSM—and even further accuracy with almost below the neck in a .300 any bullet. A change Winchester Magnum. of .01" in seating This also applies depth can result in to a bunch of other dramatic changes in cartridges. A 175-grain some rifles. Just be Sierra GameKing, aware seating bullets for instance, actually closer to the lands protrudes less below normally results in the neck of a 7mm higher pressures. Remington SAUM case This increase usually than it does into a 7mm isn’t enough to be This95-grainnoslerBallisticTipis Remington Magnum’s dangerous, but it’s a seatedtolonger-than-standardfactory much longer case. good reason to start overalllengthinthis.243Winchester If we’re really with the bullet seated casebecauseofthelongthroatina worried about long as close to the lands as single-shotrifle. bullets taking up possible, then backing powder space, we it off .01" at a time to see if accuracy should be equally worried about both improves. short and long cartridges, but the fact Another common notion is longer is it doesn’t matter, even if we decide bullets take up too much powder room to use an ultra-long monolithic such in short cartridges, because the base of as the Barnes TSX, Hornady GMX or the bullet pokes too far below the neck. Nosler E-tip. These bullets penetrate so There are several problems with this deeply that dropping down a weight or theory. First, a longer bullet doesn’t two leaves plenty of room for powder. A decrease case capacity very much. 168-grain Barnes TSX or Nosler E-Tip, For instance, a 200-grain .308" Nosler for instance, is only slightly longer than Partition bullet is 1/10" longer than a a 200-grain Nosler Partition. 180-grain Partition. A typical .300 WSM A little more reflection reveals WWW.GUNSMAGAZINE.COM • MARCH 2010