Understand that anything that moves the cam angles
away from each other reduces the amount of mechanical extraction.
-Truing up the internal lug abuttments
moves the angles apart because the bolt is now further rearward.
-Facing off the back of the bolt lugs
moves the angles apart because the bolt is now further rearward.
Even if you're only talking about a total of .005-.006 total material removed in both operations, the amount of mechanical camming for extraction has been reduced. Since the interfaces of the receiver cam surface and the bolt cam surface are angled, now the mechanical camming 'work' happens across a shorter amount of surface, over a shorter amount of bolt rotation and the bolt has to rotate further 'up' before the camming starts. If the bolt fit is loose in the raceway, this also adds to the issue as the back of the bolt moves upward when opening and the cam angle(s) interface can become further reduced. Spreading out the 'work load' always pays dividends.
Whether it's "..always necessary", obviously it depends on how much camming the receiver and bolt have before any machining is done. At a minimum, they need to be checked and corrected if needed.
The late Stan Ware (SGR Custom Rifles) was repositioning bolt handles as part of his 700 work as far back as the late '80's. I have quite a few 700 receivers that Stan massaged...most with enlarged raceways and his one piece bolt sleeve. The 700 receiver for my 250 Ackley didn't require Stan to do any handle repositioning, which was unusual.
On earlier 700 receivers that had been 'trued up', you can get a basic idea of the camming it had by looking at the gap between the front of the handle and the handle notch in the receiver.
The later unmodified 700 receivers (in the CNC era) with the notorious 'no cam' issues can't be evaluated this way as the bolt tube itself is different from the earlier bolts. Dan Armstrong has commented on this several times and explained the differences.
Here's an example of spreading out the load and taking full advantage of the cam angles. The original bolt handle (bottom) on this custom action had only the forward edge as the contact surface to the cam angle on the receiver. You can see in the picture that it had already started to wear the lower edge...which gives a hint. As well, the edge-only contact area on the bolt handle acts to pivot the the handle on the bolt tube, despite it being silver soldered and bolted on. This culminated in the infamous
'Red Hammer Incident' that's still being talked about in our region.
Parts, pieces and parts of pieces went everywhere...some are still in the soil forward of the firing line at the Holmen Rod and Gun Club in Holmen, Wisconsin.
Stan fitted a new handle (top) and profiled it to match the receiver cam angle:
Here's how it cams after being corrected. This action had multiple other issues that Stan also corrected.
My 2 cents worth, for what it's worth. Coffee at Wall Drug (Wall, South Dakota) is only 5 cents so my 2 cents just gets you 40%....
Good shootin' -Al
