I wanted to try seating a 155 lapua scenar to 2.890 and see if it will help accuracy. I originally tested them at 2.755 and got a decent group but wondered if touching the lands would improve it in a tikka ctr? Not sure if it is too far out of case to be safe?

The only way to know if it will improve accuracy is to try it.

As far as increased pressures go, based on observing velocities in my own experimentation it is my belief that pressures begin to increase when you get to within about 0.010" of the lands. You're pretty far off the lands at this point if you know that 2.890" will be touching lands. Maybe a few rounds at a lowered powder charge would be the smart thing to do.

JMO.

Thanks sound wisdom, my concern besides pressure is the bullet in the case far enough? Qill it cause an issue since it is not deeper in case?

Why are you changing .135 in one jump? Why not try .010, .020, etc. off the lands first. Also you should have enough bullet in the neck to give adequate neck tension and maintain straightness. Will a 2.890 OAL cycle through your action OK?

I started with the recommended coal of 2.775, referenced hodgon. I did a typo on the 2.755. I decided to then use the powder charge that worked, which was max and compressed. I will download and work up again at the 2.890 then move back in .30 increments to see which is best?

As long as enough shank is in the neck to keep the bullet from wobbling and wandering, there should be no problem with shallower seating. Either your throat dimensions or magazine box will determine maximum COAL otherwise.

FWIW, I always try to start about 0.020" or so off the lands. I have found that with bullets I use, about 0.020" to 0.030" off the lands seems to work. Some bullets might like longer jump, some less.

Many will tell you that large increments is the way to go, and they're speaking from their own experience. I sometimes vary by about 0.003" increments or decrements, but have resorted to 0.020" or 0.030" increments a time or two. If it can be predicted, it's beyond my talents and expertise.

Like RiverRider, I always start at max mag length, or .020 off the lands, work up to pressure, then tweak seating depths. When seating deeper I also proceed in .02 increments. 2.890 is about max in my 6.5 CTR.

Seating a VLD type bullet into the lands may produce the best accuracy, this especially in a target chamber. It is not desirable for a hunting load. I chased the lands in one 243 and when I use it in another the bullets want to stay in the barrel. I had assumed a longer seating was good for the single shot but it turns out to have a shorter throat than my Rem. short action. I start long just short of magazine length and work backwards. If best accuracy occurs when you are back to the original seating depth then it could be worthwhile to try smaller increments. Frequently there will be more than one optimal seating depth.

Oops I just reiterated JGRaider and RiverRider.

Thank you for all for the input. This is great place to get knowledge and help from