BMCM nailed it. Missing inner spring.
Good news is that its a 4516 no dash. Thinnest and lightest of the 4516's. Think 3913 on steroids.
Get an inner spring and go enjoy that fine 45. But do as BMCM advised and replace the inner spring before you shoot it. There were right at 5000 examples of the 4516 no dash made before it was discontinued. No sense risking damage to such a fine pistol.
mpi as far as I know, there was not a 4516TSW. While one should never say never where s&w is concerned, I have never even heard of a 4516TSW being prototyped.
The closest you can get to a 4516TSW, IMO, is a 4516-3. It has a few TSW features such as the larger barrel hood and MIM hammer and trigger. Hope this helps! Regards18DAI