I may have missed the bleeding obvious here, so i am sure i will be told if I am wrong but surely the optimum length is when you chamber a round the bullet gentely touches the breach rifling. As i batch reload all my cases for a batch are the same and trimmed to the same length after use. Then i resize a case and without a primmer add a bullet to the case and then gently load closing the bolt very slowly this should force the bullet into the case so when you unload it should give you the optimum length.
So if you now reload to this length there should be no gap between your bullet shoulder and the breach rifling. Hence a better group. Most factory rounds are loaded very short to accomadate all rifles.
Now you did say it:-
I may have missed the bleeding obvious here
and boy have you
the optimum seating depth will vary with bullet shape/type and powder burning rate. What flytie has found is two positive or negative,
depends on whether the barrel is at the top or bottom of it's arc, timing nodes. Best accuracy is when the bullet leaves the barrel at the exact point when the barrel is at maximum deflection and is about to reverse direction, in that split second the barrel is
stationary and so if the bullets leave the muzzle at that point then then should land in a nice tight little cluster. But if they leave the barrel whilst it's swinging through it's arc in the middle somewhere the group will more than likely be strung out.
I don't fully understand the maths behind it but you can work it out and the Quckload programme has such a feature once you have a few basic mesurements.
Now back to the real world rather than the one of mathimatical theory
in my rifles I have so far never found having the bullet in or near the leade to provide the best accuracy depsite what the "
Experts" write in the magazines/articles etc. I have found a deeper seated bullet has provided the accuracy and and consistancy I require. Some rifles due to the long leade it's actually impossible to seat some/any bullets so they can touch the leade and remain in then case neck such as the 6.5x55 Sporterised Swedish Mauser.
As Finnbear points out our courting diaster
it's just a matter of time before it goes wrong and either your left with an action full of unburnt powder when you extract the round or something goes wrong with the pressures. Bench rest techniques are best left there on the bench and have no real applications in the field just as a Formula one car has no real application is daily traffic
.