Kissing the rifling

Guns Magazine, August, 2004 by Charles E. Petty

If you are trying to squeeze the best accuracy out of any rifle the most productive thing you can do is find the seating depth the gun likes for the bullet you are using. Very often this will be longer than any factory load.

The important thing is that the bullet be aligned perfectly with the centerline of the bore as quickly as possible. The limiting factor is almost always going to be the available magazine length but any rifle, regardless of action type, can usually be coaxed into better accuracy by changes in overall cartridge length.

Typically folks would prepare a dummy cartridge leaving the bullet seated to a shallow depth, smoke it with a candle, and then seat the dummy round in the chamber. The bolt will push the bullet in and leave a solid mark in the soot.

Then you could see when the bullet contacted the rifling and adjust from there. One of the flies in this ointment is that the overall length of bullets is a big variable, so if we measure off the tip of the bullet we won't be terribly precise. For most rifles that really is good enough and involves no additional expense.

Right Tool For The Job

But to do it precisely you need to be able to measure off the bullet ogive and for that you need some special--but not very expensive gear. The best I've used is the Stoney Point Overall Length Gauge. It has two elements. First is a modified cartridge case for the caliber you want and a holder to let you put the thing in the rifle's chamber.

All you do is put a bullet down inside the case, insert it into the chamber and then using the push rod slide the bullet forward until it stops. There's a set screw to hold that measurement, which will give the overall length to touch the rifling. You'll need something to push the bullet out of the chamber and a wooden dowel is best since it can't damage the crown.

Every make or weight of bullet within the same caliber may well turn out to have a slightly different result. In other words you can't take the measurement you got from a Hornady bullet and expect it to work with a Nosler. Ain't gonna.

The second part of the system has a series of interchangeable inserts that are caliber-specific. You get the one you want, attach it to a caliper with the holder provided and read the maximum overall length for the specific component. It is actually a very easy job.

$64,000 Question

But how close should we set our bullet's ogive to the origin of the rifling?

There aren't any laws covering how we should seat the bullet in relation to the rifling, so the final decision has to be made by trial and error. But that doesn't mean there aren't some guidelines. With rifles from .22 to .25 caliber I start with the bullet .010" off the rifling. For the majority of .27 or .30 caliber cartridges my starting point is .020" and for the super magnums or anything larger I make that .050".

The first thing I'll do is work up to the maximum published charge for the powder I'm trying in 2-grain increments. With most I load just three rounds and shoot groups and chronograph at the same time. You can tell pretty quickly if a powder is going to give you the velocity wanted for the cartridge and get a good idea of how well it's going to shoot.

The next step is to work the overall length closer to the rifling. I do that in .005" increments. We could do smaller changes, but we're really more interested in trends than absolutes right now. Once more I'll just do three-shot groups and see what happens. My experience has been the .22s and 6mms like to have the bullet just touch the rifling.

Pressure Cooker

One thing we have to keep in mind is the effect of changes in seating depth on chamber pressures. Most loading manuals tell us the length at which they tested and as long as we don't seat the bullet deeper, pressure will be okay and may even go down a bit. But when the bullet gets close to the rifling it may start to encounter a little resistance when it starts to be pushed down the bore. Seating a bullet out to touch is very likely to do this and it's wise to reduce charges a grain or two and work back up if you want to start with the bullet touching the rifling.

When we get up to .30 caliber or larger diameters it seems as if they like the bullet to be .010" to .020" off the leade and one must take due care when seating closer. In many "hunting" rifles the actual limiting factor is going to be the magazine. If you're loading for a gun where you intend to feed from the magazine, it might be expedient to find out the maximum length cartridge the magazine can accommodate and still function properly. Then use that as the starting point.

You will almost always see accuracy improve just by seating the bullet out a little further. Notice I said almost because guns like to mess with our minds sometimes.

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