Hello Irish,
You are correct about how sensitive the barrel and the barrel support can be. I have been working on different barrel support /material in order to shoot both the 20's and 25gr. The slightest change in pressure throws off the groups, as well as temperature. By that I mean shooting on a warm 65 degree day combined with the barrel heat changes the firmness of the rubber support as compared to a 40 degree day. Look for a material that is heat stable, I see some guys using roofing rubber which maybe a good option. I have not tried any but its on the list. I'm also working on a barrel band to help with consistent barrel support pressure.
I also agree, if your gun shot well and consistent at one point you should be able to dial it back in. Although it can be time consuming and frustrating at times. Especially when you shoot 3 to 5 rounds dead nuts, reset the target, reload................AND its all over the place again !
Its a great cartridge for sure, but a real rifle challenge. Good luck, keep us updated on your progress.