Spent several hours in the shop today doing the measurements and writing a rough draft of the barreling process. But I hit a BUNNY TRAIL!#@$%!
My process is quite time consuming as I dont think clearly, these days
! So I started back at step #1. Here I found an anomaly that YOU Barrel fitters need to watch. When you set yourself to do a barrel job, the ACTION MUST BE as good as it can be. Its all, about relationships and it may take you some time to learn this on your own. So I'll give ya a short cut. The threads need to be square with the bore of the receiver. On this action, they are. I use a threaded mandril to face the receiver and it screwed into the receiver with no binding of the shaft in the bolt bore. This is good enough for me. This mandril, I made and it is larger in diameter than the actual bolt body. It is inside the receiver about 7" length, inside the bolt bore with no binding. That is dang straight, without an optical comparator, a temperature controlled machining environment and professional grade tooling!
Next step, I measured the newly machined face to the receiver locking lugs. Parallel within less than . 0005"! This is measured with a depth micrometer that is calibrated only in . 001" increments. Good to go! Then I thought I would slap some Dykem on the bolt locking lugs and double check engagement. Lo and Behold, the top lug was full engagement, but the bottom lug was hanging out in mid air!!!
:--)#@$%!
You dont lap-in large dimensional anomalies! You will roll off the lugs and create a mess! What to do?? How do ya measure?
As mentioned above, I had refaced the bolt and trued the bolt head in a LaBounty bolt fixture. So I took a lathe bit blank and used it as a platen across the end of the bolt. Using the 1" Micrometer, which is graduated in . 0001" increments, I measured from the back side of the platen to the locking side of each lug. What I found is that the top side lug was . 0025" longer than the bottom lug (top and bottom when bolt is closed in firing position. ) (I will double check these dimensions with a machinists flat and height gage. ) These are the critical locking surfaces. I will have to reset the bolt body in the fixture and carefully remove . 0025" off the back of the top lug. Then I will lap the lugs together. Next, I will remeasure and recalculate my headspace and tenon lengths!!!
Now, a note that could be critical. The locking lug is at 90* to the bolt body. However, It is not a 90* corner where they intersect. If you look with magnification, there is a radius transition. This radius is there to prevent stress cracking.
If you dont want to mess with this kind of detail. One can buy a PT&G replacement bolt. If there is to much difference in lug engagement, I would have done that myself! We are dealing with a pressure vessel, right in front of your brain housing group!
Without correcting this detail, the bolt would flex upon firing. It could shorten case life and create accuracy issues at a minimum.
GregH
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