Well here goes.
This is what we start out with. This is a Rem 700 reciever but it basically holds true for most modern receivers.
On the bolt you can actually see the poor lug contact on the top lug and the damage on the bottom surface.
Here the receiver is fitted into the accurizing fixture. You can see the two sets of four adjustment screws in the front and rear of the fixture used to dial the receiver in perfectly to the axis of the bolt way.
The fixture is chucked up in a four jaw chuck and the visible run out of the fixture has been adjusted out. The precision mandrel is shown protruding from the receiver. This receiver is not to have the bolt sleeved so the mandrel is riding in properly fitted bushings in the front and rear of the receiver.
The dialing in process has started by using the 0.001" indicators to dial in the receiver.
After the mandrel is dialed in to less then 0.001", the coarse 0.001" dial indicators are replaced with the fine 0.0001" indicators and the receiver is dialed in until the needles simply do not move. This can take considerable time but is well worth the effort in the end result.
Here are the results of a freshly cut set of receiver threads. These threads are single point cut using a matching set of full profile thread cutters. These special cutters cut only a specific thread pitch and a new set is needed for each different thread. Also they are in a matched set so that the internal threads on teh receiver perffectly match the external threads on the barrel shank for a perfect class 3 thread fit which is critical for extreme performance.
Step two, recut the bolt locking lug recesses. The receiver is still soaked in cutting oil but it is clear that the locking recess is totally clean and has a high quality machined finish ready for lapping which will only take a few minutes with a receiver printed in this manor.
This is the finished receiver after the receiver face is inside chamfered and trued. The receiver is now ready to build on after bolt lapping but first the bolt needs to be accurized as well.
Here the bolt has been fitted with the precision arbor in the rear of the bolt body and inserted into the 6 jaw chuck. The bolt nose surface, bolt nose diameter, front surface of the bolt lug and rear surface of the bolt lug have all been trued.
The collar has also been fitted and turned true to the axis of the firing pin hole. The steady rest is then used to support the collar and bolt so that the bolt face can be trued.
Here is the freshly trued bolt face. Only taking enough to totally clean up the bolt face. This is generally around one or two thousandths at most.
This is the finished bolt. You can see the difference in the finish of the forward surface of the recoil lug compared to the bolt face. The forward lug surface is not a baring surface, only cut for consistant and accurate clearance to the barrel recess. The bolt face on the other hand is a friction surface and as such is cut to a very high quality finish to reduce friction with the case head when closing the bolt on snug cases.
This is the finished product. This receiver did not have the bolt sleeved to the customers request. One the receiver gets to this point, measurements are taken from the closed bolt face to the forward edge of the recoil lug.
This measurement combines all the critical dimensions except the axis of the receiver threads to give a measurement of how square the machining is.
These critical surfaces are:
1. Forward surface of the recoil lug
2. Rear surface of the recoil lug
3. Face of the receiver
4. Receiver bolt lug recess
5. Bolt lug locking surface
6. Bolt face.
If any of these are out of square it will show up very visibly on this measurement. Four measurements are taken on the four corners of the bolt face. All need to be within 0.0001" or the receiver is not ready to lap and buld on.
If this turns out I will be amazed.