Re: bolt lug contact
Here are measurements I take after accurizing a receiver to confirm that the receiver is square and ready to build on. I do not measure before accurizing because if it has not been accurized then it will not be square, simple as that.
All receivers that come into the shop to be rebarreled that have been accurized before are also all measured to confirm squareness and all measurements are reported to the owner as proof of needing to be trued or as being ready to build on.
I do not accurize receivers that don;t need it but I also don;t build on unsquare receivers either unless told to by my customers, as you know, the customer is always right!
Step one, totally clean the receiver and bolt.
1. With a 0.0001" depth mic I take a measurement from the receiver face to the baring surface of each bolt lug recess in the receiver. Must be within 0.0001"
2. Measure thickness of each lug on the bolt to confirm uniform for proper consistant barrel clearance. Again, must be within 0.0001"
3. Measure from leading edge of bolt nose to the front surface of each lug. This tells me if the bolt nose length is uniform.
4. Take a measurement of the bolt nose diameter but this is only to get correct dimension for fitting the barrel bolt nose recess but will include it here to show all the steps I take.
5. Again varify the receiver lug recesses are totally clean as well as bolt locking lug surfaces are also clean and insert the stripped bolt body into the receiver and put bolt in the locked position. I then put the recoil lug that will be used on the rifle on the vertical positioned receiver and take four measurements across the bolt face. It is critical that the bolt face be clean as well.
These measurements are taken at 12:00, 3:00, 6:00 and 9:00 around the bolt face. this is the critical measurement as it combines all mating surfaces in the receiver, bolt, barrel relationship to tell you if the system is ready to build on.
I personally require that these four measurements have no more then 0.0002" variation total and much prefer to see less then this.
This also tells me that the recoil lug is also square and ready to be used in the build.
As long as the receiver threads have been trued properly, a receiver with these measurements is ready for building on.
With proper barrel fitting techniques and chambering techniques, the axis of the bore and chamber and receiver will be in perfect axial alignment and all will be perfectly square as well.
As you can see, the barrel needs to be pulled to take these measurements!!
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