Was thinking about seat depth and pondering over the affects of it as a whole. Without getting too scientific if possible, should we look beyond the fact that it has an affect on exit timing which will affect the load tune. Is this dependent on time of travel down the bore or the amount of bullet (length) actually held by the case neck (neck tension) or both ? How about case capacity and pressure relations ? Are we also tuning these parameters as a side affect and are those more a part of the total tune than most of us think about ? Or maybe not thinking about it ? Looking forward to your thoughts.
Your contemplations are valid
especially in relation to depth affecting the volume of the container
but in just about every rifle I have loaded for
I have noticed, those other things you mentioned, are such a small fraction of the influence seating depth has on exit timing itself, that they are irrelevent.
If we can see that a Tuner changes the barrel in its position with relation to when the bullet exits
How can we not also arrive at the conclusion that when the bullet exits is also just as important?
---
If we for instance, suddenly seat .040" deeper, then that it a different story, and may require a charge change of a few tenths to compensate
I am more speaking of changes in a few thousandths to perhaps .020"
the rest being irrelevent
I say this because quite a few of my rifles, once I find the middle of the window, have been so forgiving I can seat +/- .010 of the middle of the window and have it shoot the same
tested on paper out to 600 yds mostly.
I keep a lot of my good groups, and throw away a LOT of test groups, even though they are valid repeats of the good groups otherwise I could provide them as evidence if say .030" difference in seating deth and have it still shoot just as accurate.
----
this could also be in my case, that I dont chase high velocity
I only go for accuracy which may even mean 200 fps slower than is possible with a particular cartridge
I will accept 200 fps slower when the load, seating depth is so forgiving...
it shoots the same always, every month, at every temp
---
When i chase near the peak of velocity, it is not so forgiving and so much more fine tuning is required.
For my ELR rifles which are already fast to begin with, 200 fps slower isnt really slow by comparison to other cartridges though which is why I accept this.
---
with my 100 yd rifles, I think you may be on to something here, and this to me is because the case capacity is smaller and therefore any very slight or small change to seat depth or charge weight is actually significant by comparison to larger cartridges such as 22-250 and above.
Meaning, lets say we change seat depth by .010" in something like a 22 BR...
...this may mean we have to now adjust charge weight a few tenths also.
However, - once I find a seating depth that is best for that rifle (base to Ogive or CBTO)
that measurement to the Ogive, stays the same for any bullet used.
---
It could also be, the time taken for the bullet to slam into the rifling and begin to establish harmonics of the barrel, is the important factor, more so than the base of the bullet leaving the barrel.
Which we would be adjusting the starting time of barrel harmonics vibrating.
I'm thinking this theory has more validity since we measure and adjust based on Ogive (Front) of bullet
vs the base, or when the bullet actually exits the bore.
---
I only adjust the charge weight after seat depth has been found, and charge to fine tune it in.
Like if I switch from a 50gr, to a 52 gr, to a 55 gr
I may adjust charge a little bit, but seating depth stays constant.
