I don't necessarily agree with this statement, shooting context is important. The "ideal" seating depth is one that is sufficiently far out in the neck that it allows you to take full advantage of the available case volume and get the most out of whatever the intrinsic BC of your bullet choice happens to be. Anyone can load up rounds at a reduced charge weight and lower velocity and obtain decent precision. However, if you're giving up a significant amount of performance or diminishing brass life markedly because the bullet is sunk way below the neck/shoulder, I can pretty much guarantee you that some of your competitors won't be doing the same thing, and will have sufficient freebore in their rifle to seat the bullets they're using optimally. In F-TR, the .223 Rem is already at a disadvantage to shooters using a .308 with 200+ gr high BC bullets. There is no good reason to give them any further advantage if you happen to shoot a .223 Rem by using a bullet that is too long for the specific rifle chambering.
You have my attention, Ned.
You are correct that shooting context is important, so let me share with you some additional info. This is a jack-of-all-trades .223 with a 26" tube. I shoot an F face in a club division called F-practical (harris bipod and rear squeeze bags only, no mechanical rests or joypods)-think of it as a PRS rifles shooting F class faces. Other than that, I might shoot it in Any/Any slung as it is legal in several classes and also a reasonable offhand rifle (XTC). This is not a dedicated FTR gun and I do not compete in FTR nor have the expectation of competing with an FTR rifle purpose built for that purpose. My rifle is nearly 5# below the FTR weight limit. My last match, I didn't have this bolt gun build done, so I shot this division for the first time with my 18" AR15 with 15x optic and handloads. The 193 at 500 was not only the highest 500y score in my division, but the 3rd highest of any shooting F-faces. My little 18" AR outshot several F-open rifles. I was experimenting with different loads and only Agg'd 566, but this not only won the F-prac division (against 6.5 creedmoors and .308s), but was only 9 points below the FTR winner. Nine points behind a dedicate FTR gun (and division champ) with a production 18" AR, untested loads, and a 15x optic is in my view surprisingly competitive. And I derive great satisfaction achieving respectable results from lesser gear.
So now my jack of all trades rifle is built. And I intend to give the FTR guns a run for their money with a lighter weight rifle, a field bipod and no bunny bag. I don't have any plans to travel to Nationals and am content to shoot club matches. And if I can post respectable scores on F-faces with a little .223 and no $1500 rest or other goodies, that's a successful outing for me.
That's the relevant context.
So,
if one puts aside case capacity, what is the theoretical advantage of the "ideal" seating depth of having the boattail/bearing junction above the neck/shoulder junction? With my particular brass and powder, I can hit 2750 with case capacity to spare at a good accuracy node in a 26" bbl. It seems to me that the case capacity is only relevant if it's limiting your ability to hit a reasonable speed with good accuracy.
I've tested up to 27.0 with acceptable pressure. I could likely go 27.3 or so and easily hit 2850 or more at my current short OAL. But if it's less accurate, it seems pointless to me. In my rifle, the 88s like a jump of about .050".
Accuracy> speed.
It seems to me that the "ideal" seating is only consequential when you need the extra capacity to hit a higher accuracy node in a given barrel because the lower nodes are far too slow to be competitive.
A ballistic calculator will indicate similar windage for an 88 at 2750 as you'd get with an 80 at ~2900 or a 75 at ~3100. I have been testing 80s, but seem to be very close to pressure around 2900.
I'll need to test my 80s more to see if I can push them fast enough to offset the BC penalty relative to 88s at even 2750. With another powder, I might be able to hit 2950 or so with the 80s.
Anyway, I'm willing to hear someone out and hear their best argument, but I will do things as I see fit. Actual results trump theoretical problems every time.