BC kinda thought so myself when first seeing it - minus the ring cuts. However the winchester website leads me to believe otherwise withthe following statement taken from their PR:
This is achieved with a web of copper jacket material that mechanically locks the bullet together. In addition, a bonded (soldered) rear lead core locks the lead to the jacket. The bonding allows the lead to stay with the jacket during impact, resulting in nearly 100% weight retention and more energy deposited on target. The patent pending design yields a unique two-stage expansion at both the front and in the body of the bullet, resulting in massive knockdown power. The XP3 bullet is capable of penetrating through tough bone, but still allows significant expansion in lighter, thin-skinned game like deer.(
http://www.winchester.com/news/newsview.aspx?storyid=149)
Barnes MRX's core is made up of Tungsten, they make sure to distance themselves from lead core bullets when talking up the MRX.
Here's a pic of the MRX:
