I don't know if this topic has much relevance but I figure I'll put out some info on chamber fluting anyway. Back when I was thinking about making a cetme in 7.62x39 the big hangup was needing to flute the chamber for the rifle to function. After a week or more of head scratching I finally decided that the best way to control the depth of the flutes was to use my (home made) CNC mill. My intention was to make a cutter that could be inserted into the chamber, drop into the back of the rifling and then pull it out using the X and Z axis programmed for the shape of the chamber.
I spent a bit of time in CAD drawing the chamber cross section and finally came up with a tool that was stout enough to withstand the cutting pressure while still small enough in diameter to fit inside the bore.
This is a close up of the actual cutter:
Cutter inserted into the chamber:
My first fluting experiment was done using a cheap VZ58 barrel. I figured the $25 barrel was a great learning experiment. I ground the tiny carbide insert cutter by hand, and didn't know what to expect. The mill was programmed to the chamber contour and the spindle motor was unplugged so i didn't forget and accidently flip the switch.
Here is the finished VZ chamber:
I took a mold of the chamber and discovered that the flutes were too shallow. Fluting a chamber is a lot like driving a submarine. You gotta trust your numbers because you can't see what is happening. I set the barrel back up in the indexer and cut them again.
Here's a photo of the shallow first mold on top and the more pronounced fluting on the bottom mold:
Once I had the programs finished for the 7.62x39 I bought an RPK barrel, faced it off and rechambered it for use in the cetme and fluted it for the build. I used the RPK barrel because of it's large OD which I could turn down to fit into the cetme trunnion.
This weekend I started fluting in 7.62x51, more on that in a bit.