Recently got a Stoney Point OAL gauage and bullet comparator and starting seating out closer to the lands so my free bore is .030 on some recent reloads and found a signicant difference in the point of impact. Federal Gold Medal match rounds I had had about .060 of free bore and when I fired the handloads with only .030 the rounds grouped about 4 inches higher from 100 yards! Quite a difference - the handloads are moderate too only 42grs of IMR 4064. This is for a .308, not that any of this makes much matter but was quite interesting to me anyway.

I've never done it, but my 'smith says he can alter the seating depth and walk the bullets right across (up or down) the target. If he says it, I'd believe it. Ku-dude

What you're doing is altering the barrel time of the bullet. When the bullet is seated deeper in the case, it takes it longer to exit the muzzle.

Since we know that the muzzle "whips" with the harmonic whip of the barrel, altering the barrel time will naturally change the point in space where the bullet is released.

I hope this clears things up, if not, ask and I'll clarify.

The above is precisely why my load development method (the OCW load development system) calls for fine tuning of the load with seating depth changes only after the optimal charge weight of powder has been identified.

Forgive me for saying so, but gauges which tell you how far from the lands you are actually encourage you to work backwards, in my opinion.

Best of luck with your loads. If you have any IMR 4895, try 43.6 grains with the 168's in your .308. Test this load beginning a caliber's depth in the case (.030"). I think you'll find that it will perform very well in your rifle.

Take care,

Dan Newberry
green 788