I spent the money on the riveting tools too, even though I really couldn't afford it. I took some backdoors and was able to get some cheaper by not going through the normal channels for some tools.
My advice would be to start where ever you feel comfortable. I have never built a screw-gun, but have heard nothing but good things about them. I think it is a matter of opinion and choice. Here is my opinion. If I had to start all over again, I would probably have gone with a screw job because it does require less tools and is normally faster. After all, if you do end up liking this hobby you can take the screws out and rivet it all up later.
So back to your question. If you are doing a screw build, I would follow the guidelines that most guys use for the correct depth to drill. I don't know the numbers, but Cephus is probably right on the money. Be very careful though. Many people drill to far and go into the barrel when doing the front trunnion. If you are doing a rivet build, you have a few options. Some leave the barrel in and drill the rivets out very carefully and use the barrel as a "bucking bar" to set the rivets. But, most remove the barrel and then drill out the rivets completely. The rear trunnion, doing a rivet build, can be a real pain. You can drill all the way through the trunnion and then step up your drill size until you drill out most of the rivet. Then take pliers and a punch and try to get the rest out. Another option is to file the ends all the way down flush with the trunnion. You could then try to punch them out, or drill half way through, insert the punch and hammer it out while supporting the trunnion. There are many ways. Like Scubdvr said, learn how to use the search tool and you will find many ways. Just my .02!
Welcome to the site, by the way. You will find the most knowledgeable and friendly guys on the internet who know AK's!
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