I'm new to the AK47 type rifles and was looking at a new Sierra Arms AKM 7.62x39.  Are these any good?  What are the differences between an AK and a AKM?  Thanks for your help.  Steve.

I dont know about the Sierra Arms product.

An AKM is the stamped receiver model. (M=modern),
for manufactoring referance. Anyway, the AKM is stamped,
uses a smaller dia. barrel, different FSB, and a few other
items that are different than the milled "AK47".

The " AK47" isnt really a proper designation for the earlier
milled version, but it has been used for decades, and most
of us use it also. The milled receiver, thicker barrel, different FSB,
and some other changes tell it apart from its stamped (AKM)
brother.