On an accuracy build with an action that has very consistent outside dimensions, .0015 movement is the outer limits of acceptable for myself. Most of the time, you can get them to .001 or a smidge below. This is my Mack Bros. single shot done recently:
On this Model 70 that just got finished up, it started out with .026 movement:
When it was finished, it ended up having .003...about as good as a Model 70 will ever let you get.
Much of that is due to the flat area behind the recoil lug, which on Model 70's is
never flat. When they mill the threads for the action screw, that thread milling process...since it doesn't cut but rather displaces material...can raise the material around the threaded area. This one had material raised 90 degrees from the threaded hole, as the light cut with a diamond file shows. In the end, I milled .006 off this flat area before it was truly flat. The action screw hole was also not exactly 90 degrees to the flat which resulted in the action screw pulling the receiver down at a few degrees of angle.
Another thing to be aware of on
any receiver is stamped in numbers, etc. It might look neat to see those in reverse in the finished bedding but all they do is cause little stress risers that compromise the bedding job. On Model 70's like this one, I file the area flat to eliminate any raised edges and then fill them with JB Weld and let it set up for 24 hours. Then the final bedding is done. Any little bit of ridges remaining need to be lightly touched with a small flat diamond file to remove any edges. On this Model 70, I checked it just for grins before doing that and it was .007 movement. Just taking care of those ridges brought it to .003.
Another thing to keep in mind when you're checking the bedding with an indicator is the type of action screws you're working with. A flat-to-flat action to pillar screw will 'fall away' quicker than an 82 degree tapered seat screw. I use a lot of the large 82 degree screws and make the seat in the pillars to match them. A quick lapping of the mating surfaces always pays dividends.
If the bottom metal is an 'active' part the bedding...in other words if the action screws tighten against it...the bottom metal/trigger guard needs to be properly bedded to the stock so it doesn't flex when the screws are tightened and transfer that stress to the receiver.
Another thing to remember is that if the barrelled action is excessively tight in the bedding, you can sometimes see very little indicator movement. This does not mean the bedding is stress free...quite the opposite.
For what it's worth. -Al
