That is the twist rate of the barrel? Measure it if you don't know.
Are your bullets matched to that twist rate?
My bet is you have a 1:14 twist for 68 grain match bullets. That twist is way too slow for the heavy bullets you are shooting.
Custom target rifles are often built to shoot one specific load. That means one bullet type/weight, with that bullet seated a specific distance from the lands. If you don't have everything right, you'll get 1.5 foot groups.