I have been loading some Barnes 130GR TTSX BT in .308W and have been puzzling about the COAL.
The cases are FL resized and trimmed to 2.005"
The Barnes quoted COAL is 2.810"
Max COAL to lands length measures as 2.925" with a 150GR TTSX
Because the bullet length varies by up to + 0.003" (due to the plastic tip seating depth not being consistent) I have assumed I am better off setting the Lee Seating Die to yield 2.810" on a short bullet and ignoring the eventual COAL of those with the extended tips...
The 2.810" brings the 2.005" case mouth to just include the middle cannelure. If I use the Lee Factory Crimp die it will just foul on the lead-in to the cannelure and possibly alter the seating depth tiddlywink style. The depth will only alter by a couple of thou at most, so not a great problem.
Should I adjust the crimp pressure to be sufficient to take the inner surface of the case mouth to the bottom of the cannelure or does one rely on the tapered form of the crimped case to bear on the shoulder of the cannelure 0.050" back from the case mouth?
Or would it be better to...
a) seat the bullet 0.030" deeper (COAL 2.780") and crimp on to the section between the cannelures or
b) 0.50" (=COAL 2.860") further out and again crimp on to the full diameter section
c) not bother about the crimp at all and just leave it at 2.810"?
Any thoughts, advice or experience please?