OAL

Just remembered that arsenal made 30-06 match ammo originally had both asphalt sealant in case necks and case mouths crimped into cannelured bullets. When production resumed after WWII in the early 1950's, tests proved accuracy was better when bullets were not cannelured nor crimped in place. The cured sealant had enough grip on the 173 grain bullets to require at least 20 pounds of force to pull bullets from the cases.

The last stage of case forming was to expand the case mouth to a thousandth or more than bullet diameter. But leaving a small "donut" at the case shoulder. The warm sealant was smeared around inside of the case neck then a bullet was seated. Bullets often rested crooked as the sealant cooled and dried.

This is the main reason bullet runout in arsenal match ammo is up to several thousandths. I've seen up to .007" on both 30-06 and 7.62 match ammo.
 
Last edited:
That matches what was in A. A. Abbatiello's old study of runout effect on accuracy, but I have to say I've achieved 0.008" runout myself by seating 168-grain SMK's with a Redding standard seating die into resized LC 30-06 cases. It was back in the '80s that I first got a runout gauge and became aware of it. At the time, I was unaware of the use of the Lyman M-die to enable bullets to start into the case mouth straight. I tried the trick of rotating the case as the bullet was seated in steps, but it didn't help much. In '89, when Redding came out with their Competition Seater Die I got one and it reduced my worst-case runout to 0.002", the same as the offset in the worst-case neck wall thickness runout.

I think the one-caliber seating depth is one with which many guns seemed to work well enough in terms of accuracy, and I expect it made a lot of gun writers comfortable that they were securing the bullet well enough for self-loading. It is also in the ballpark that enables a lot of assembled loads to fit into magazines easily. Overall, those add up to making it a reasonable broad ballpark recommendation. I found that much seating depth to be a good accuracy seating depth with many bullets in my old '96 Mauser in 6.5×55, for which I wanted to fit the rounds in the magazine. I've also found that bullets that have a good accuracy node seating depth near the lands will often have a second one deeper that can correspond to close to a caliber of seating depth (did in the Mauser), but not always. "Not always" is the problem. There are so many exceptions out there that I've stopped considering that I will find an optimum seating depth without experimentation.
 
Too bad commercial runout gauges don't use the same front reference like the rimless bottleneck cartridges use when fired. Commercial gauges use a point on the case body next to the shoulder. That point is clear of the chamber wall when fired. The back of the case at its pressure ring may be off center a thousandth or so against the chamber wall.

Such cases have their shoulder hard pressed into the chamber shoulder where they center perfectly. Runout gauge's front reference should be a round hole whose diameter is about midpoint on the case shoulder.

The further the dial indicator is from the front reference, the greater runout will be seen on the dial. Some standard dimension should be established for each cartridge so comparison between reloaders results would be meaningful.
 
Last edited:
My first cartridge concentricity gauge was the Bonanza unit that became Forster's later. It supports the head and the bullet tip. This was the style Abbatiello used for his 1960s study of 47 lots of NM ammunition, and it will measure how far off the overall cartridge axis a bullet tip is tilted if you add in a little calculating. At the time, I wanted an apples-to-apples with Abbatiello's method, so it was fine for that. It will not give you a bullet centering number at the case mouth, though, which your gauge concept would add into the mix, if I understand it correctly.
 
Then there's the situation where a crooked case neck perfectly aligns it and the bullet on the chamber and bore center when its pressure ring is off center at the back of the chamber to do that.

A perfectly straight cartridge with its back end a thousandth off center in the chamber will have its bullet tip off center in the throat one to two thirds that much in the opposite direction as it pivots about its shoulder against the chamber shoulder.
 
Last edited:
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.
 
Unclenick said:
I wish there was one universal recipe for centering that worked for all, but it doesn't seem to be so.
Click to expand...
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.
 
Last edited:
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.
 
Unclenick said:
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.
Click to expand...
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.
 
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.
 
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.
 
Last edited:
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.
 
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.
 
Last edited:
You must log in or register to reply here.
Back
Top