OAL

[Unclenick]

Yes. There are lots of potential accuracy-deteriorating aspects of the problem. With secant vs. tangent ogives, making the secant ogive shoulders sharp, you find they start into the rifling at bore diameter at the beginning of the throat where the freebore ends, while tangent ogives touch the rifling at the bore diameter of the throat first. The latter is thought to center the bullet better, accounting for tangent ogive bullets being more forgiving of small tilt errors than secant ogives are. This inspired Berger's hybrid ogive design that is tangent at the shoulder with the bearing surface and switches to the lower drag secant form at a few thousandths under bore diameter.

I've seen some handloaders report getting significant group reduction from outside neck turning to help to center their bullets, but others who got nothing but tired fingers from it. There's one such example written up in the 1995 Precision Shooting Reloading Guide, but the rifle in question is a 300 WM, for which, if the shooter was headspacing it on the belt, it makes almost no sense it would matter. If he was headspacing on the shoulder, though, then it makes sense, and I don't recall his mentioning that.

I wish there was one universal recipe for centering that worked for all, but it doesn't seem to be so.

[Bart B.]

Originally Posted by Unclenick

I wish there was one universal recipe for centering that worked for all, but it doesn't seem to be so.

Minimal full length sizing without expander ball has the best track record. Makes the biggest groups the smallest possible.

Sierra Bullet's tool and die makers Ferris Pindell and Arvin Martin along with ballistic technician Martin Hull deserve most of the credit for convincing reloaders to do that. Especially competitive rifle shooters.

[Bart B.]

For those wanting the smallest runout numbers for their bullets, this one from Hornady will probably do it...

https://www.hornady.com/reloading/pr...entricity-tool

It has the shortest distance from front reference to the dial indicator touch point on the bullet. Only half an inch or less as shown in the picture. Move the indicator closer to the bullet tip to get less runout readings.

[hooligan1]

John Barsness wrote an article on this very subject stating that if you want least runout, and still use an expander, use the die where the expander die is being withdrawn while some of the neck is still in that part of the die.
Which brings me to the Forster Bonanza Benchrest die, mine seems to work really well.

[Bart B.]

Originally Posted by Unclenick

I've seen some handloaders report getting significant group reduction from outside neck turning to help to center their bullets, but others who got nothing but tired fingers from it. There's one such example written up in the 1995 Precision Shooting Reloading Guide, but the rifle in question is a 300 WM, for which, if the shooter was headspacing it on the belt, it makes almost no sense it would matter. If he was headspacing on the shoulder, though, then it makes sense, and I don't recall his mentioning that.

That usually makes case necks inside diameters more uniform.

Some people years ago used the Lyman M die in new belted magnum case necks for the same reason. Excellent accuracy in match rifles. Often better than full length sizing once fired cases.

[Unclenick]

Interesting. The M-die has gained some re-popularity because the little step it forms in the neck lets you set the bullet straight upright in the mouth so it runs into the seating die straight, which reduces fiished cartridge runout.

[Bart B.]

measured my 30 caliber bullet seaters for .308 Win., .30-06, .30-.338 Win Mag and .300 Win Mag to get the bullet chamber (freebore?) diameters where the bullets are held just before they start into the case neck:

Wilson BenchRest chamber type .308, circa 1966;. . . .3105"
RCBS standard .308, circa 1966; . . . . . . . . . . . . . . . . . . 3100"
RCBS standard .308, circa 1979; . . . . . . . . . . . . . . . . . . 3115"
RCBS competition .308, circa 1980's; . . . . . . . . . . . . . . 3107"
RCBS standard .300 Win Mag, circa 1999, . . . . . . . . . . 3104"
RCBS standard .30-.338, circa 1967,. . . . . . . . . . . . . . . .3102"
Bonanza BR Competition .30-.338, circa 1980. . . . . . . .3093"

30 caliber bullet diameters range from .3070" to .3092"

I've clamped 7.62 M118 match ammo necks in 33 caliber collet type bullet pullers then gently pushed the case rim to bend the body straight with the neck axis as its case head centered on a magnum shell holder in the press ram just below the case head. Runout of the bullets dropped to. 001" or less from over .005" before bending. Accuracy improved a lot. The press ram head needs to have near zero misalignment with the puller axis.

[Unclenick]

Interesting that the seaters all measure ±0.01 at point of contact. The one I know won't follow the pattern is the Lee Dead Length Seating Dies, which have a small seating ram that acts near the bullet tip.

That collet sounds like a good anchor for flexing. A collet in a lathe would be even better, as you could turn the spindle by hand and use a dial indicator to show the runout at the back end of the case body to let you know when you had the job done. I bought a D4 collet chuck and a set of collets in 1/64" increments a few years ago, but it didn't occur to me to apply it to this task before now, so thanks for the idea.

[Bart B.]

Unclenick, you're welcome. A bullet puller collet chucked in a lathe is 3.1415962... times better than any commercial runout gauge by my calculations.

When I shot on a military team, the manager of the shop that built our rifles suggested two ways to improve the accuracy of the 7.62 M118 match ammo issued.

Run all ammo through a concentricity gauge then sort them. Those with runout over .003" would be put back in the 20 round box indexed high point towards the box front. Index them at 12 o'clock in the chamber when single round loading for 500 yards and greater. Use the straighter ones at 200 and 300 yards. Perfectly legal in EIC leg matches as the ammo wasn't altered in any way.

For all other matches, seat all bullets a few thousandths deeper with a Lyman 310 tong tool. This broke the sealant uniformly setting bullet release force. Then sort them by bullet runout.

Much better scores resulted. Regular M118 match ammo often tested well over 2 MOA ES at 600 and 1.5 MOA ES at 300 in the best converted Garands. These procedures reduced test groups by a third or more for non-leg matches.