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by John Barsness


IF WE WANT to get the most accuracy out of our rifle, the bullets in our handloads must be seated straight. If not, then all the rest of the steps are pretty much wasted effort.

We want straight ammo because a bullet that starts down the bore at an angle also tends to leave the muzzle at an angle. Now, all bullets "precess" as they leave the muzzle, meaning they aren't spinning perfectly point-on. Instead the tip of the bullet wobbles like a pass thrown by a 10-year-old quarterback. Normally this precessing soon stops, calmed by the spinning of the bullet.

A bullet that leaves the muzzle with its point off-center tends to precess more wildly, and sometimes never does calm down all the way. Plus, the bullet may even be deformed by starting down the bore slightly sideways. Neither helps accuracy.

In handloading "straight" means the center of the bullet lines up with the center of the case. Now, there are degrees of straight. For anything short of a dedicated benchrest rifle, we simply are not going to be able to seat every bullet "perfectly" straight. With typical varmint and hunting rifles this doesn't really matter, because the tolerances in their chambers are a little loose, even in custom rifles, in order to allow functioning in the field. So what we're really trying for is pretty darn straight, a technical term meaning "as good as it gets."

When loading for big game rifles, bullet "run-out" of no more than about .005", as measured a tenth of an inch in front of the case mouth, generally obtains all the accuracy possible from a typical factory big-game rifle. With custom rifles, or factory varmint rifles, .002" is a worthy goal. I own one heavy-barrel Remington 700 chambered for the .223 Remington that's capable of putting five shots into ¼ inch or even a little less at 100 yards, when good bullets are seated with no more than .002" runout. Varmint accuracy just doesn't get much better than that, especially without a super-shooter on the trigger.

We can test ammunition for straightness without any fancy tools. A small wall mirror or even a very smooth tabletop will reveal any run-out over .005". Just roll a case across the surface, and if you can see the bullet "wobble," then run-out is more than .005".

But this only tells us if bullets are seated straight after the fact. We need to know a couple of other things before we seat bullets.

First, we need to know if the wall thickness in the necks of our brass is reasonably even all the way around, within .001" or so. If not, a seated bullet is going to be off-center in the case. Wall thickness is easily measured with tools, but can also be seen. If we place our cases in a loading block, then look directly down at them, any significant unevenness in neck-wall thickness can be spotted. (A magnifying glass helps, but I'm nearsighted so don't need one. I just take off my glasses.)

Next, we need to get the neck of the case straight before we seat the bullet. The big problem here is that the common design of resizing die features an "expander ball." because commercial brass tends to differ in neck thickness, not just from brand to brand but from case to case. In a typical sizing die the neck is first sized smaller than it needs to be. Then, when the case is pulled out of the die, the expander ball "bumps" the inside of the neck up to the correct dimension for holding a bullet.

This is fine, except that pulling the neck over the expander ball can also pull the neck of the case off-center with the case body, partly because the case can tip slightly in the shellholder. Note the word "can." Many full-length dies will size cases pretty straightly, with no more than .002" neck run-out. But if they don't, then various techniques can help us do better.

First, we can polish the expander ball, or substitute a carbide ball. Either helps the ball slip through the neck more easily.

Second, we can first size all the cases without the expander-ball assembly, then push the expander ball through the neck of each case. But when we push the case up into the die, over the ball, the bottom of the shellholder pushes squarely against the base of the case, and the expander balls centers the neck. (Here decapping, however, has to be done in a separate step.)

Third, we can buy a die that doesn't feature an expander ball. These squeeze the case neck from the outside, rather than expanding it from the inside. Lee Collet dies and Redding "S" dies are examples. The Lee die will work on any neck thickness, while the Redding dies require the correct bushing for different neck thicknesses. Both work very well.

Another helpful technique is case-mouth chamfering. Most of us do this anyway, unless we're using boattailed bullets, but the common tool for the job puts a fairly steep chamfer inside the mouth. Much better is a very gentle taper, allowing the bullet to slide easily into the neck. Tools for the job are available in various catalogs.

Many handloading articles suggest seating each bullet only about halfway, then turning the case 180 degrees before finishing seating. I have tested this a number of times and my run-out tool never indicated much difference. What made a real difference was using a dedicated, precision seating die. These have closer tolerances, especially inside the "neck" of the die, where the bullet fits as it's being seated.

If the bullet must be crimped, make this a separate step, since crimping as the bullet's being seated can also knock the bullet out of alignment. First, adjust the die to crimp the case mouth, per the instructions. Next, back the seating die out of the press very slightly, and seat all the bullets to the correct depth. Then remove the seating stem from the die, run the die all the way into the press, and crimp all the rounds.

You'll eventually notice that some bullets tend to seat straighter than others. In general, boattailed hunting bullets often seat straighter than many flat-base bullets. I suspect this is one reason why some rifles appear to "like" one bullet more than others. It's also probably the reason many hunters think boattails are more accurate, when in reality flat-bases tend to shoot a little better-if both are seated straight.

Even with al these steps, a few rounds will end up with slightly unacceptable run-out. I correct these with a series of holes drilled in the 2x6 that form the face of my loading bench. These holes are just about the size of bullets from .22 to .45 in diameter. If a bullet is seated a little out of round, I push the bullet into the correct hole and "bend" it back into alignment.

All of these steps will do as much for accuracy as all other handloading steps combined.

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2009

quote:

From the Barsness article:
In handloading "straight" means the center of the bullet lines up with the center of the case.

quote:

...because the case can tip slightly in the shellholder. Note the word "can."