Reaming out the throat on a 7MM Mag
I have a question about how difficult and expensive it would be for me to have a gunsmith lengthen the throat on my Winchester Model 70 Black Shadow, in 7MM Rem Mag. I find that I have to seat bullets quite deep (shorter than SAAMI specs) to get rounds to chamber easily in this gun, so I bought a Go/NoGo gauge and the headspace is fine. Also chambered an empty case and the chamber doesn't seem tight. I used a magic marker to blacken the bullets on several loads and kept seeing marks from the lands, even when seating the bullets very deep (COL = 3.100). So, I'm pretty sure I'm dealing with a throat that is considerably shorter than it should be.
I've heard experienced shooters talking about how some cartridges that have excessive capacity for the bore (220 Swift, 6.5 Rem Mag) erode the throats over time. I don't know if that is likely to happen with a 7MM Rem Mag, but I am used to loading rounds longer than SAMMI specs, not shorter. I bought this gun because of the long-range capabilities and I wonder how much velocity (don't have a chronograph but will buy one this summer) I'm sacrificing to the deeply seated bullets? Accuracy seems good to excellent, depending on choice of load.
What I'm really hoping to find out is how complicated and expensive it is for a gunsmith to correct this problem, and if it's worth getting it done or not?