Yeah, guess I'll have to contact S&W. I've torn down a lot of guns, but not the 4013. I figured if it looked too difficult, I'd take it, and the parts, to my local smith. We have a reputable one fairly close. In fact, I should probably just call him; he might even have a spring in his stock. Thanks.
Probably best to let a smith familiar with S&W TDA pistols handle the chore for you. It's not that the actual replacement & gentle peening of the rivet is difficult, but that you have to get the drawbar out of the frame. While the frame can be stripped and the drawbar removed in a couple of minutes (by someone familiar with doing it), learning to do without damaging something during disassembly & reassembly is the real trick. Some of the video links of stripping 3rd gen guns have made me shudder a bit.
FWIW, out here the CHP actually started removing the TP springs and drilling the drawbar heads (wallowing out the rivet hole) to prevent future installation of them in older 4006 series guns, and then ordered their new TSW's made without the springs even being installed in the first place.
The TP spring does help reduce some of the "play" (looseness) in the SA trigger mode, but unless you're looking for it (doing slow-fire target shooting), it's not like most shooters would ever notice it being gone, especially when running the gun in fast-paced shooting drills.
I once did an extended 2-day sessions of drills, firing more than 800 rounds, and at some point both prongs of the TP spring snapped off in that gun. I have no idea when it happened, as I wasn't stopping to take the time to careful inspect the trigger play in SA mode during that time. It didn't affect function, so I didn't notice it, whenever it happened.
Most of the folks who have broken TP springs in duty weapons never notice it, bringing the guns to the attention of our armorers for some other reason (usually nasty, fouled weapons that have been abused and/or overly-saturated with solvents & CLP until function issues develop).
Funny thing is that while the TP spring only serves a purpose in TDA guns (DA/SA), since the drawbars used to be pulled from the same bins during production, the DAO guns got drawbars with TP springs. Complete waste of time in a DAO gun, as their isn't a cocked/SA hammer mode.
I chuckled the first time I was told that they'd decided to just go ahead and use drawbars with TP springs installed, for both TDA & DAO guns, as it was easier to just have ONE bin of drawbars on the assembly line.
