357 Sig Bullets
Not following your initial question. If you are asing if the Wal-Mart Winchester 357 Sig ammo is usable in your 357 Mag pistol, then the answer is no. If you are asking if the Winchester 38 Special or 357 Mag ammo THAT IS loaded with the the 357 Sig bullet is useable in your 357 Mag pistol, then the answer is yes.
I'm guessing that due to the recent ammo demand, Winchester settled on a common bullet to use in all three loading.