Please explain something to me if you will. I may have been breathing to many fumes from the lathe so bare with me [img]/ubbthreads/images/graemlins/grin.gif[/img]!
If you take two cases, both using a 300 gr SMK 338 bullet.
Both seated to the same 3.675" oal.
IF you take the two cases and give them both the exact same shoulder configuration and shoulder diameter, But have one case that has a case body length and case length .100" longer then the other one, How exactly does the shorter case have more volume?
A perfect example of this is my 270 Allen Mag. The original design was based on the 338 RUM case with very similiar case dimensions as what you listed you want in your 338 Thunber(good design by the way [img]/ubbthreads/images/graemlins/grin.gif[/img]!!)
Based on the 338 RUM case, the original 270 Allen Mag formed case would hold on average 118 gr of WC872 when filled to the case mouth. This was an average of 10 cases.
In testing I quickly discovered the the 270 bore diameter could easily handle more case volume with the heavy bullets and forming out of the longer 7mm RUM cases was simplistic to the extreme so I redesigned the reamer and tested the new 270 Allen Mag design based on the 7mm RUM. From the Shoulder/case body juntion, the two designs were identical to the case mouth. Shoulders were identical in angle and diameter and the case necks were also identical in length. Only difference was that the 7mm RUM based 270 Allen Mag had a 0.090" longer case body then the 338 RUM based version.
In measuring the same number of 10 cases with the new 270 AM design, the case capacity when filled with the same WC872 to the case mouth had increased to 126 gr.
So given the case shoulder and necks volumes are identical, the longer case will have 8.0 gr more capacity then the shorter case design.
Now rememeber that bullet seating location is unchanged, both are seated to an over all length of 3.675" to feed through the Rem 700 mag box. Since the longer case provides more case volume AROUND the bullet and farther up the bullet, it offers more capacity over the shorter version of the 270 Allen Mag. It also added roughly 100 fps more velocity potential as well.
This pic shows the difference between the 257 Allen Mag(left), original 270 Allen Mag based on the 338 RUM(middle) and the final design of the 270 Allen Mag based on the longer 7mm RUM case.
You can see that all three are loaded to the same 3.675" oal to feed through the Rem 700 receiver but it is clear why the 7mm RUM based 270 AM offers more capacity then the 338 RUM based version.
The 338 RUM and the 338 Edge are exactly in the same boat as the 270 AM. Only real difference is that the Edge has a longer body portion of the case.
That said, with your design, you can match the capacity of the 338 Edge in a shorter case, no arguements from me there. My 257 Allen Mag(338 RUM based) has more capacity then a full length 7mm RUM case because of its improved case design.
That said, if I put the same configuration on the 7mm RUM, the longer case will provide an increase in capacity over the shorter length case.
The limiting factor here is the magazine box length. If we are limited to say a 3.675" OAL. The only way to increase powder capacity once you have improved the case design to the limit is to put more powder capacity around and up the bullet body. This means pushing the shoulder forward so that there is less bullet sticking out of the case.
Do not look at this as seating the bullet deeper into the case capacity because you are not. You are fixed to the 3.675" OAL, all you are doing is pushing the powder capacity up around the bullet to increase it without increasing over all length of the loaded round.
Well, if that maked any sense, feel free to reply!!!
Have a good one,