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Old January 16, 2019, 05:00 AM   #1
jonnefudge
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Bullet Concentricity important?

I have just drilled my seating stem to fit vld-bullets. It is probably not as precise anymore. How important for accuracy is bullet concentricity when seating the bullet?
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Old January 16, 2019, 05:05 AM   #2
std7mag
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Very important.
I'm sure others will be on here shortly to give you the scientific explanation/aspect of it. Lol
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Old January 16, 2019, 08:47 AM   #3
cw308
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J
Your loading low drag bullets for long range shooting 300 yards and out . Making our reloads as accurate as possible . You would have been better off calling the die company to send you a VLD stem . I see posts on drilling out the stem but the bit has to be dead center , not many can do that with regular home tools . How far are you shooting and how much runout are you getting ?
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Old January 16, 2019, 11:53 AM   #4
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bullets are like people, electricity and water. When being inserted into a case neck that is smaller in diameter than the bullet itself it will follow the path of least resistance. If the neck is concentric so shall be the bullet unless you can make your neck go oval instead of round
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Old January 16, 2019, 11:54 AM   #5
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You mentioned bullet seating die modification and concentricity of bullets. Are you talking about bullets being out of round or concentricity of finished cartridge?
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Old January 16, 2019, 02:15 PM   #6
jonnefudge
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Finished cartridge. Shooting distance up to 1300yards. Just ordered a new vld stem.
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Old January 16, 2019, 02:27 PM   #7
rg1
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The old rule of thumb for seated bullet concentricity is .002" or less for targets and .004" or less for hunting rounds. Of course zero would be best if possible.
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Old January 16, 2019, 05:05 PM   #8
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Im with 308 and rg1
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Old January 16, 2019, 07:06 PM   #9
hounddawg
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http://www.nielsonbrothersarms.com/2...centricity.htm

some hard numbers from a test using .22 LR in a test facility
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Old January 19, 2019, 01:53 AM   #10
Metal god
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Quote:
I see posts on drilling out the stem but the bit has to be dead center , not many can do that with regular home tools .
I drilled out one of my stems with a hand drill while holding the stem in the other , worked out great. You just need the right diameter bit so the original part of the stem that contacted the ogive on regular bullets also contacts the VLD's ogive . All I really did was make room for the tip of a VLD tip rather then make a new point of contact for the stem . Not sure it would work the other way around , changing a VLD stem to better fit a standard ogive . I'd think you'd need to be centered up in that case .

I've since bought a new die with interchangeable stems but the old die works just fine still . The interesting thing I've founds since doing all that is realizing how different the ogives of bullets are in shape and length resulting in some fitting well in the stem while others kind of rock back and forth . Having one custom fitted/molded to your specific bullets would be the best idea I'd think . I kind of remember reading there is a seating die manufacture that does that very thing . You can buy a stem for the 190gr smk specifically or any other popular bullet . Forget the brand though , sorry .
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Old January 19, 2019, 06:51 AM   #11
AVirginian
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Whidden will make custom stems, though I don't know if they will fit other dies.
they seem to be $40 per.
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Old January 19, 2019, 08:19 AM   #12
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Lacking a concentrically tool/gage, am still using the roll the loaded cartridge on a flat surface technique. If wobbling is evident, may want to consider evaluating why.

Concentrically may be one of the top accuracy concerns leading to buying a good Match seating die.
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Old January 19, 2019, 08:36 AM   #13
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Back when we were loading for long range the rule of thumb was if it don't go in straight it don't come out straight.
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Old January 19, 2019, 10:44 AM   #14
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Concentricity is important. At least it is to bench rest and thousand yard shooter, the rest of us, not so much.
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Old January 19, 2019, 01:48 PM   #15
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Quote:
Concentricity is important. At least it is to bench rest and thousand yard shooter, the rest of us, not so much.
Most of us interesting in the subject are at least various types of bench rest shooters.

Houndogs link is truly amazing amount of work (astonishing actually).
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Old January 20, 2019, 05:41 PM   #16
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The results vary with the bullet. In the '60s, A. A. Abbatiello measured concentricity on samples from, IIRC, 42 lots of National Match ammo and got 1 moa wider groups from 0.004" of tip-tilt off-center. Beyond that much tilt, additional tilt made little additional difference, as the bore straightened out anything much more than that. This was 30-06 ammo using the 173-grain M1 Type bullet. When Harold Vaughn did it with stubby 6 mm bullets, the same amount of tilt gave only about half the dispersion.

The differences include how many calibers the bullet bearing surface is (longer is straightened out more by the bore) and how far forward of the geometric center of the bearing surface (where the tilt is centered) the center of mass of the bullet lies. The further forward (or behind) the center of mass, the bigger the orbit it has around the bore line for a given degree of in-bore tilt, so the greater is orbital speed. When the bullet exits the bore the bullet is tossed at that speed radially away from the mean trajectory path in a direction tangent to the bore where it is nearest to the center of mass at the moment of release. The drift due to that tangential toss was on the order of half a foot per second with the National Match ammunition, and that is too slow for drag to have much effect on during bullet time of flight, and thus it stays with the bullet all the way to the target.
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