While the two are somewhat similar in external appearance, the STG44 and AK47 are very different rifles internally. Basically the only thing they have in common

While the two are somewhat similar in external appearance, the STG44 and AK47 are very different rifles internally. Basically the only thing they have in common mechanically is that they both use a long stroke gas piston, along with many other contemporary small arms (Garand, BAR, Bren, DP, etc).