Necessity is supposed to be the mother of invention. I'm sure that was the case when it comes to the AK-47 shown below. Not only does it use a guitar strap for a sling but it has a rather unique buttstock to say the least.
This picture is from a post on The AK Forum which was seeking unique examples of AKs for a calendar. I believe the poster called this the Poppy Farmer Special. There are a lot of other nice examples but none so unique as the one above.