The best available body armor with the best plates will stop a 30.06 FMJ class round. This would be the Interceptor type vest with plates which provides Level IV protection. It's a bit cumbersome at ~17 pounds and it's not something the cops would wear on their daily rounds.
What the cops typically wear is either a Level II or IIIA vest.
Level II isn't much: 9 mm FMJ, at ~1,175 fps or, with extra Kevlar (22 layers), a .357 JSP at ~ 1,395 fps.
Level IIIA is better but is still only "pistol caliber protection":
9 mm FMJ at ~1,400 fps or .44 Magnum at ~1,400 fps with extra Kevlar (30 layers).
So given what the police typically wear...... if they wear any at all on daily patrol..... just about any "deer rifle" round will penetrate their armor. Heck a weak-butt AK-47 round will easily penetrate what the police normally wear without any sort of Teflon coating on the bullet.
Point is, the whole "cop-killer" aspect is hype. Just about any deer rile round is a "cop killer" given the light armor they use.