Bullet seating depth: on both ends.
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 Weatherby-made 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 Weatherby rifles have all featured either monolithic bullets such as the Barnes Triple-Shock X-Bullet and Nosler E-Tip, or heavier lead-cored bullets with long shanks, whether heavy Hornady Interlocks, Nosler Partitions or Sierra GameKings.
Softer bullets, especially in lighter weights, can vary considerably in their reaction to seating depth. One of the softest bullets on the market is the Berger VLD. Often these shoot best when actually touching the lands, but in some rifles they prefer considerable jump.
In fact, some experimentation in seating depth often results in better accuracy with almost any bullet. A change of .01" in seating depth can result in dramatic changes in some rifles. Just be aware seating bullets closer to the lands normally results in higher pressures. This increase usually isn't enough to be dangerous, but it's a good reason to start with the bullet seated as close to the lands as possible, then backing it off .01" at a time to see if accuracy improves.
Another common notion is longer bullets take up too much powder room in short cartridges, because the base of the bullet pokes too far below the neck. There are several problems with this theory. First, a longer bullet doesn't decrease case capacity very much. For instance, a 200-grain .308" Nosler Partition bullet is 1/10" longer than a 180-grain Partition. A typical .300 WSM 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!
A little research into various loading manuals shows when a 200-grain bullet is loaded in a .300 WSM case, the powder charge has to be reduced about 2.5 percent. This isn't because the longer bullet takes up more room, but because a 200-grain bullet creates more pressure than a 180. So the "loss" in case capacity doesn't mean a thing, the reason a 200-grain bullet works just fine in the .300 WSM.
In fact, if we do a little more math we find out a 200-grain Partition sticks way down below the neck of long 30-caliber magnums. If seated to normal overall cartridge length a 200-grain bullet extends just as far below the neck in a .300 Weatherby Magnum as it does in the .300 WSM--and even further below the neck in a .300 Winchester Magnum. This also applies to a bunch of other cartridges. A 175-grain Sierra GameKing, for instance, actually protrudes less below the neck of a 7mm Remington SAUM case than it does into a 7mm Remington Magnum's much longer case.
If we're really worried about long bullets taking up powder space, we should be equally worried about both short and long cartridges, but the fact is it doesn't matter, even if we decide to use an ultra-long monolithic such as the Barnes TSX, Hornady GMX or Nosler E-tip. These bullets penetrate so deeply that dropping down a weight or two leaves plenty of room for powder. A 168-grain Barnes TSX or Nosler E-Tip, for instance, is only slightly longer than a 200-grain Nosler Partition.
A little more reflection reveals another basic truth: A bullet's base takes up just as much powder room inside the case neck as it does below the case neck. One handloader I know is so obsessed with the sin of a bullet extending below the neck that he's developed several wildcats by pushing the shoulder back on a standard case, resulting in a longer neck, so the bullet's base will never intrude into the case body. He thinks his special rounds should result in more velocity, but all he's doing is losing the extra powder space around the base of the intruding bullet.
Yet another factor is today's denser powders. We have an enormous selection of finer-grained powders to choose from, ranging from Alliant's Reloder series to Hodgdon Short-Cut Extremes to Ramshot's clean-burning ball powders. Some of these powders are even specifically designed to work in short, fat magnums.
The one real concern with some newer bullets is whether the bullet can be seated to the optimal relationship with the lands. Bullets like the Berger VLD and any of the sleeker plastic-tips have very long ogives. When seated so the rounds will work in a conventional magazine, they often end up a long way from the rifling, so there's no way to experiment with seating depth. Sometimes the bullet will even end up with the rear of the ogive inside the neck. A little way inside doesn't matter, but sometimes there isn't enough neck contact to hold the bullet firmly.
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|Date:||Mar 1, 2010|
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