Mitchell.
Runout wont give you vertical stringing. Vertical stringing is caused by variation in velocity, variation in neck tension, veriation flash holes, variation in primer seating, variation in primer pocket depth, and in a Handi latch movement and poor and uneven flash charges caused by by burrs on the inside of the flash holes.
Variation in powder charges as little as 0.2gr in the 223, 204, 222 will do it. A powder with 100% filling ratio should be considerd. The case volumn in these wee cases vary as much a 3.0gr Ho2 from one maker to another. The 204 load you were using was actually 58K
The same load in a case with 3 gr less volumn was well over 72k
Except for the latch movement all the above will come about by pressure variation. In a BR rifle halve a bullet diameter in vertical is a bad news.
You talk about runout what do you use to measure it, and how do you correct it. Where on the cartridge is the runout, and or where in the chamber does it occure. Where in relation to the chamber do you seat the bullet.
Indexing loaded shells is of some help in a crooket chamber or in crooket dies. Most dies including Lee dies will produce concentric ammo, providing the neck walls are perfectly reamed to a consistant wall thickness and later on checked for brass flow into the neck walls.
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