I am shooting a load in my 6.5 X 55 that the previous owner of the gun worked up. It is an accurate load but I want to "tinker" a little bit. Seating depth for this load is 0.2 off the lands. If I move the bullet out to .02 off the lands, am I correct in assuming that I will most likely have a decrease in pressure? If this is true, then it should be safe to leave the charge as is, without reducing and starting over, correct?

I know some of you use OAL for FINAL tuning, but this is such a drastic change, I wondered if it would be a problem. I mean, as it stands, the bullet is really deep in the case, and I wondered if such a drastic change could get me into an "under pressure" problem.

OR, maybe I should just leave well enough alone. After all, I did shoot a .25" group with it!!

2/10" off the lands is pretty far back but if your rifle shoots there I wouldn't mess with it.

If you move your bullet out (makeing the OAL longer) so that your bullet (the ogive) is only 2/100" off the lands you could see a significant pressure INCREASE, not a decrease. Any time you make a move toward the lands that dramatic you need to back off your load a bit.

Let me add that you will probably have some decrease in pressure casued by moving the bullet out because you are not filling up the combustion chamber (the inside of the case) as much but that will be small compared to the pressure increase mentined above....the overall effect should be a pressure increase.

Some people will tell you just the opposite; that deeper seating makes a smaller combustion chamber and raises pressures.

Actually, pressures are not likely to change to a detectable degree. Moving the position of the bullet has neither increased nor decreased the friction-free combustion chamber (the volume of space rearward of the base of the bullet when the groove-diameter portion of the bullet engages the lands). You may or may not experience a change in the accuracy of the loads.

Pressures sometimes jump when the bullet is seated to actually engage the lands.

If you seat the bullets far enough out to actually kiss the lands you should see a sharp increase in pressure.
A friend and I tried to seat some hunting bullets just a little bit shorter than kissing the lands. About 2 or 3 in each box would appearently just kiss the lands because they showed severe primer flattening and loose primers. Presumably there is some variation in how the bullet seater collar pushes the bullet.
For this reason I would recommend seating off the lands by at least 0.03" Take my word on this. You absolutely don't want to have primers falling out of the pocket. Scary thing.

Stonecreek is correct. Due to the slow-burning nature of rifle propellants, the bullet has actually moved a considerable distance down the bore before peak pressures occur. This is the reason why it is ESSENTIAL that a bullet be freely released by the case mouth/neck, in order to prevent dangerous pressures. However, a considerably oversized bullet, IF freely released by the case neck, will swage down and safely travel through a much smaller bore. This is why P.O. Ackley used to offer a substantial reward to anyone who could PROVE a gun had been blown up (or to anyone who could blow one up in his presence) by shooting an oversized bullet. His only condition was that the chamber of the gun had to have a neck portion of sufficient size to freely release the bullet from the case neck upon firing!! If is did, NO DESTRUCTIVE PRESSURES RESULTED from firing oversized bullet. For example, an 8mm Mauser bullet (.323") in a .308" bore, or a .308" bullet in a .26 caliber bore!!