OK now lets tie all this together. The first thing to do is file the different flat widths we've cut into that wasp waist shape between each feed rail. Had we been using a CNC we could have programed this step hit the RUN button and watched these mirrored contours take shape.
Instead we must make the modification blend by hand. This is best done with 6" to 8" medium cut mill files followed up with a # 4 cut file blending our stepped cuts together in an uninterrupted transition from front to rear. Since we made these mill cuts into the rails with use of the digital readout, both the depth and length these two apposing sides should blend out in almost a mirror image. The upper and lower edge of each rail must also be filed with a slight corner breaking radius. The transition along both rails should feel smooth and interrupted. The plan is to just blend these milled flats not hog out more rail width than is necessary.
Then starting with 180 grit W&D paper both rails should be polished top and bottom, front to rear. This sand paper work should be continued up through 320 grit. Keep the radius theme on both sides of the rails
Next you need to file an angular ejection bevel on the underside right leading edge of the rear bridge as we have left a very sharp corner that will catch on every cases being ejected. In addition any sharp corners generated by and end mill need to be chamfered with a file and then paper.
You must remove the sharp corner at the rear of the feed well wall that we've generated by widening the feed well. 1st with a pillar file, then a stone and finally with paper we need to turn that sharp corner into parabola shape. Failure to do so will cause the belts on the case to hang up on that sharp corner.
Next we begin blending the 90 degree shelf above the leading edge of the magazine box ID we have established by cutting the feed well forward with the existing angle of the 30/06 bullet ramp. Some would suggest making this new angle straight from the top of the mag box to the rear edge of the flat behind the lower recoil lug seat, you could. However if you blend the standing material into the established bullet ramp angle with again a parabola shape you will in fact be leaving much more steel in the ramp area than Winchester ever left behind on factory 300 H&H receiver. This leaves the lower lug area with significantly more material and removes the knife edge effect at the top of the bullet ramp found all too often on a factory 300 or 375 H&H receiver. Another advantage of this extended parabola shaped ramp also puts the bullet nose in contact with the ramp sooner allowing the bullet nose to begin its rise towards the chamber as well as rolling the base of the case into the bolt face and under the extractor sooner. Remember the beaten to death term "controlled round feed" in my experience the sooner this control starts as the bolt is pushed forward the better the entire concept design becomes.
Say what ?????????
As an example the extractor groove diameter on a cross section of six different manufactured 300 Winchester cases I measure a while ago showed a + and - .020 variation in the six brands of brass.
The fit of the extractor hook to the chosen manufacture case should allow the extractor spring away from the bolt body .004 to .006 when the case is rolled and centered into the bolt face in the chambered position in my opinion.
The larger the bullet diameter or the further away the bullet nose is from the centerline of the action the more material will need to be removed. This can take 5 minutes to a number of hours depending on the case and cartridge design. When you feel you have the best shape working for you then you can use a Foredom hand tool with the proper sized cartridge rolls and or the rapid break down stones to go over and remove the file marks and then I paper polish entire bullet ramp. You want that bullet ramp smooth as a Beagle's ear.