What does have the firing pin bushed mean??...I've never heard of that...
Excellent question, the Remington 700 bolt design includes a firing pin {striker assembly} that floats in the forward area of the bolt. Inside the bolt there is a very rough machined surface and the striker itself is guided only by the very poor sloppy fit of the bolt inside diameter and the ring on the striker. The tip of the striker, due to this poor machine work and tolerance can hit on the side of the firing pin hole behind the bolt face. There is a machined out cone shape right where the striker tip enters to help get it started into the firing pin hole.
Because of the poor fit the striker can hit the back of the hole {bolt body} in a different spot every shot, causing inconsistent ignition, varying lock times and a different harmonic from shot to shot, thus impeding accuracy. Even if the firing pin hole is the correct size {about 50/50 chance on a 700 these days} how long do you think it will stay that way having the striker hammer it's way thru every shot??
The 700 is typically made with an oversize firing pin hole and or one that may be offset as well. All this adds up to affect accuracy. When you have the bolt bushed the bolt face is machined so a stepped threaded bushing is installed and a new firing pin hole is machined dead center. Because the bushing itself is also longer, deeper in to the bolt face the striker itself is also machined so it is held captive and under constant guidance and also with a much tighter tolerance. No more shot to shot inconsistencies due to poor machine work tolerances, roughly machined bolt bore and non-guided striker.
Just how much accuracy enhancing this accomplishes can vary from rifle to rifle. You are building a new one with what some consider a best or custom high end barrel, no doubt an aftermarket trigger and glass bedded stock {at least I hope you do these things}. With a factory barrel, trigger and stock I would not recommend that you even bother, but in this case I'd do it.
Now, all that said, you may love the benefits of a brake and would rather go that route. If you believe a muzzle brake helps you shoot better than go for it and it's probably best to do what you know and believe in over a suggestion by some guy you never heard of recommending something you never heard of either....your choice. If it was me I'd take knowing my striker assembly is working as consistent and accurately as possible every time I pull the trigger vs. four times the noise, concussion and back blast. Good hunting sir.
Edit: just an fyi...you might want to go back and like some of these post {and I don't just mean mine!!} if you feel like they have helped you. Not a requirement, but it might not be a bad idea if you want to continue receiving the best info you can get.
Also, if you are interested in getting this done contact "carlsbad". He da man!!!