December 05, 2011
George Spafford is building a replica of the Yugo M70B rifle using a stub parts kit. A new installment will appear here every Friday
Install the Barrel — Part 2
The Yugo extractor protrudes from the front of the bolt significantly. Therefore, the bolt must be stripped to headspace the rifle accurately. Stripping the bolt is actually very easy and simply requires a small punch and hand pressure to remove the two retaining pins.
Once the groove in the barrel for the pin aligns with the holes in the trunnion, it is time to check headspace. It is always a good idea to use real headspace gauges to be safe. If there is too much headspace, the resulting slop on the end can cause cases to bulge and even rupture. When I first started building AKs, I invested in a set of Manson Precision Reamer gauges — Go, No-Go and Field. They have worked great for me over the years and are a good investment.
With the Yugo bolt, the extractor is so large that the bolt must be disassembled to test headspace. Despite looking daunting, the M70 bolt actually disassembles with hand pressure by removing first the bottom pin and then the crosspin. I like to do this on a table to make sure I don't lose any little parts and then I put the parts in a container out of the way. A little organization can save some grief down the road.
Use a small tray to hold the bolt parts. They are small and very easy to misplace.
I like to perform headspace tests with just the bolt and no carrier. This way I can see exactly what is going on. First, I use the Go gauge to verify that the bolt will close properly. I insert the gauge in the chamber and then slide the bolt forward rotating it so the lugs begin their lockup.
The bolt should be able to rotate fully. If it does not, the barrel must be pressed back out. Methods include a long bolt with a double brass nut on the end to protect the breech, the use of a long socket extension with a stack of copper pennies taped on the breach to protect it and so on.
Second, I use the No-Go to verify there isn't excessive headspace. Again, I insert the gauge in the bore, install the bolt and proceed to rotate it. The bolt should stop short of full rotation. Now this is an estimation on my part, but I would say mine stop at around 80-90% of the rotation. We're talking differences in the thousandths of an inch, so I really am watching to make sure it doesn't go all the way — that is the important part. If it does, then the barrel must be pressed in further.
Most likely, with a worn M70 like mine, you will need to press the barrel in further. Any time you change the location of the pin from the original means you will need to use an oversize pin. This is done by making sure everything is in the right location and then drilling a new oversized hole with a sharp cobalt bit that is .002" smaller than the pin.
For this build, I had too much headspace, so I pressed the barrel in and opted to use 19/64 (.297") drill rod and M size drill bit (.295"). Once it was pressed in, I confirmed the headspace one more time before moving on. It's always good to play it safe.