barrafishing0 wrote:Projectiles are sierra 165gn spitzer boat tails and a box of Barnes tsx 168 boat tail ( because i could on the day)
You'll see with those how much of a difference there can be with different projectiles.
As everyone has said there are a few different tools or techniques for finding the right seating depth, I'll try and give you a bit of general info though to help you understand the concept of your seating depth though...
Standard COAL (cartridge overall length) for the .308 is 2.800". The Game Kings are a pretty good example of an "normal" size and shape bullet and if you seated them so your COAL was 2.800" they'll probably be
about right and the bullet would be 'just off' the lands.
That's a bit of an assumption but for the sake of example lets say the above is correct and when loaded like that the GK's are in the sweet spot.
The Barnes bullets are about 1.5mm longer and have a sharper OGIVE (the cone/front of the bullet). Because of this if you load a cartridge with the Barnes to be the same 2.800" length the OGIVE will be further back from the lands so the bullet will have a small amount of 'jump' into the throat when fired. This jump can reduce accuracy of the cartridge.
Because of this the Barnes bullet would need to be seated higher for a longer COAL to bring the OGIVE up to be closer to the lands.
This is a picture of a pair of Berger bullets off their website but you'll get the idea.
- berger ogive seating depth
- berger-ogive.jpg (54.77 KiB) Viewed 4867 times
Your Barnes bullet would be the left and your Game Kings would be the right bullet if you get what I mean. As you can see if the left bullet was seated to the same depth as the right bullet the OGIVE would be too far back.
All make sense?
As said there are a few assumptions and general points in there, you'll still have to find exactly what your rifle likes but I hope that clears up the general points for you?
Let me know.