The manufacturers of domestically produced AK-47 receivers generally choose to err on the side of caution where the dimensions are concerned. For example, the magazine wells are typically a millimeter or so too tight to fit magazines without force. This section is about "finishing" your AK-47 into a completed rifle which functions properly.
As mentioned above, the magazine well is typically narrow. My approach was to take a magazine which already had some scratches on its sides, and force it into the mag well. I took note of where the mag well was binding on the magazine's sides, and filed the sides of the magwell a bit. Once the magazine slid in without a big fight, I pushed the magazine in place until it clicked, taking note of where it was particularly tight. At that point, I filed down the sides a little on either side of the magazine well until it was touching, but not tight and binding.
-- SeanNewton - 02 May 2006