There is only a cosmetic difference in the bullet. Now depending on store/bullet-packaging age, you may find the SST tougher to load - due to a thicker sabot. Supposedly, that's now been simplified & the regular Shockwaves & SSTsproduced today have the same MMP sabot. Outside of all that, the only difference is price.

If you are purchasing a T/C gun, you want Winchester Triple Se7en primers with 777 powder. Copper-only Powerbelts (245-405) are popular when used with semi-medium powder loads (70-90 gr loose). The only lead Powerbelts that are good performers are the 405 grain. The recommended 338 gr. Platinum Belts seem to perform best at 120 grains (Pellets)or less. The equivalent in 777 loose powder would be 105 grains or less.