There's zero way the M1186 can realistically be expected to penetrate Level 4. As @Default.mp3 pointed out, it's the structural equivalent of M855A1 or M80A1. It's an EPR round, not a tungsten carbide AP round like M995 and M993.
One of the parts that we on the internet might be misunderstanding in this equation is whether Level 4 is actually the standard the Army is shooting for. We use Level 4 a lot, but I can't remember if Level 4 was specifically referenced in any of the briefing materials as the goal. It's very possible that the Army is shooting for GOST 5A, the current defeat level fielded by Russia's "Ratnik" 6B45 armor. That would seem much more realistic, since if I recall correctly GOST 5a is rated for 7.62x39 BZ-API.
Still, the problem with that goal in reality is that the Russians are mixing in issue of the "Granit" series of plates...in particular with the units that you really want to be able to shoot deader, quicker (SOF, crack assault/vanguard units, maybe @Caballoflaco can add more context). The Granit plates can be had up to GOST 6 (or whatever that new rating system they're using is, BR6?). This plate is capable of defeating all known AP rounds short of 50BMG API (edited to add) and M993. Note that there is no M993 analogue in the 6.8x51 chambering...atleast, not that has been made public.
So, in reality, it's still falling short from its intended purpose of overmatch/AP capability.