.308 seating depth

[johnno]

What seating depth are you using on your .308's I've got an omark with a neilsen adapter and a maddco stainless barrel. the first load I tried was 45grns of 2208 in highland cases(hey they were free) and seated them with 155gr nosler hpbt .020" off the lands and the same load at the depth of some old 144grn fmj ammo(about .100" shorter). I got no measureable difference in group size when tried at 100m and again at 500m is this just fluke or is there another explanation. Also the shorter depth compressed the load.
regards Hammer

[Simon C]

I have my 155 SMK's & 175 SMK's seated to provide a 2 thou jump. I have done little testing with this config however the results at long range have been very good. One thing I have noticed is that the OAL length of the 2 different cases are different.....this is due to the variation in ogive taper in the 175 vs 155. The variation in depth will affect case capacity & therefore pressure. The BC differences in your projectiles would also make a difference (esp at longer ranges). Try shooting those loads at 800m to get a better comparison (x2 10 shot groups). Putting them thru the chrony would be a good idea to assess the velocity spread.

[johnno]

Thanks simon but I didnt explain it properly. I'm not using 144 grn projectiles but 155's seated at the millitary depth and getting no group differences so the BC is the same but I'm suspecting the pressure is the factor.

[Tony Q]

Hi Johnno

My rifle has a long throat and as such when using 155's it has a long jump. I seat them out as far as i dare but regardless of seating depth there is no change to group size.

[Chris Burdett]

Hi Johnno,
I seat 155gn BJD,s hard into the lands, and use ADI 2206H powder. I think that there is a difference in the peak preasure time from 2208, and is ideal for .308W. On anouther shooting site it was advised that was best to avoid "no mans land" ie between .005"in/.005"out the lands as it,s hard to not have variables there.

[bully_eye]

If seating them close to or into the lands doesn't work, try jumping them .030 or so. My gunsmith said that more than a few 30cals shoot better with a bit of a jump using standard projys. VLD's like to be jammed in. FWIW I back my 185 Lapuas about .030 off the lands and see no improvement any closer- in my 300win mag that is. Even seated thenm a full calibre of the lands as an experiment.

Michael