Bill, the claim is just that. The extra weight is supposed to help counter the muzzle flip, but I put them on the scale, and the stock rsa is around 1/2 an ounce where the tungsten is around 1 1/2 ounce. Or I can say that the stock rsa is 15 grams and the tungsten is 40 grams. Not a very big difference IMO.
I needed to buy some stronger rsa's to shoot high power ammo and I had a choice of a stainless captured or the tungsten, and I figured since I was spending money on something other than food and rent that I might as well spend a little more.
The tungsten rsa's didn't break on me and I shot one box of UW 10mm 200gr tmj with both the 21 & 23 #. I also shot 20 rounds of .460 Rowland with them, I know that is not a high round count but it is a powerful round. Hopefully I will get a high round count with them.
I emailed The glock store about the expected round count on the springs and was told that I had to call in with that question, go figure...