Re: Rem. 700 Sendero Accuracy
A poor crown is certainly detrimental.
What I have seen make the biggest difference in any rifle is the overall length of the chamber. A shorter oal chamber will minimize brass flow, give more loadings and improve accuracy.
If you have access to an RCBS Precision Mic or Wilson case gauge, measure unfired brass noting the reading. Measure it again after you load it if you are a handloader. Then fire the cartridge and measure your fired case. Might want to select 3 or 4 that are the same in unfired measurement and see how they gauge after being fired.
RCBS Precision Mic is not made to perfectly mimic a SAAMI chamber, so it is only a guide. Yet, if you see the overall length of your cases before and after firing you can get an idea of the dimension of your chamber.
Most Remington chambers are a few thousandths on the longish side. You can have your gunsmith set the barrel forward to give you a .001 over minimum chamber and see your groups tighten up remarkably.
H-S Precision stocks have been traditionally torqued to 65inch pounds per H-S instruction. Might have better luck if you vary the torque from 40-50ip and try differing the values per each action screw.
Barrel might also be torqued on the receiver like it was done with a ten ton hydraulic press. If your barrel is being set forward, have the smith lap the face of your receiver and recoil lug where it bears against the receiver shoulder and rear of the recoil lug cut out. H-S Precision stocks are excellent, in my experience, but you could also lightly skim-bed your receiver to the action block.
Then there is ammunition. Unless you are handloading you won't even begin to get the control over accuracy you are seeking. Most Remington 700s will need a trigger job. About 2.5lbs trigger pull is excellent. Other receiver and bolt truing with lug lapping is not as critical as a minimum oal chamber and precision handloads. May as well save the action job for later as you may find you don't need it.
I have used J-B bore paste to remove fouling, but if you think your bore is rough, David Tubb's firelapping bullets are probably the better way to go. J-B is not meant to be a lapping compound. Ed Shilen is quoted as saying he's seen more barrels ruined from over-cleaning than anything else.