BC, are they putting in the 'Borden Bumps' or something similar.
A common problem with the solid front locking bolts actions and the need to function in the field. Tight for accuracy but no good for function. Add some slop and no real benefit over a factory action.
The bumps or shims are installed so that during the bolt closing phase, these supports lock the bolt body into the action (solid section behind the mag well). When the bolt is fully closed, there is no play in the bolt vs action raceway to ensure consistent and tight lock up during the firing process.
The bolt is also supported during the dropping of the sear to eliminate bolt bounce. Something BR shooters feel is bad for accuracy.
When the bolt is opened, these supports fall 'out of battery' leaving a loose bolt for easy function.
These tweaks have been quite popular with Rem actions before custom actions became common.
The best example of this I have used is a Parker Hale Midland ie commercialised Mauser/Springfield. The bolt has so much slop and wiggle you wonder if the bolt came from a smaller action. However, at lock up, things go into place quite nicely leaving a fairly accurate tight action.
The P Enfields solved this with helical lugs which 'pulled' the bolt into battery. A surprisingly good solid lock up. At least one custom action maker was working on locking lugs with a similar pattern. Of course, far more complicated to machine then a flat surface.
Let me know how your project works out. Give me a shout on the other stuff.
Jerry