The single stack 4013's are a little harder to find then the double stack TSW models. The double stack TSW's were based on the 69XX series and can use the full size 4006 magazine. I would actually prefer the single stack as I have discovered carrying a single stack pistol concealled is more comfortable. However, magazines for an early production 4013 will be harder to find. As long as this doesn't bother you (I know it doesn't bother me for my 4040) it is a great gun. The single stack 4013 is on my list of guns I want, but so are several others (S&W makes too many nice guns, at least enough that I don't have enough money for all of the ones I want).