Hey,
I would be happy to answer your questions regarding the standard .mil Interceptor body armor. The standard origin of the Interceptor vest is the 24 pound Ranger Body Armor Systen (RBA) which was designed by US Army Soldier Systems at the request of the 75th Ranger Regiment back in 1994. In 1999 the Interceptor vest was designed from improvements of that system by Point Blank Body Armor of Oakland Park, FL.

The Vest is really made up of two key components. First is the outer tac vest (OTV). By itself it is only rated for Level II protection The vest was tested to stop a 9 mm 124 GR full metal jacket bullet (FMJ) at 1,400 ft/s (426 m/s) with minimal deformation and has a V-50 of roughly 1,525 ft/s (465 m/s). This means that the bullet has to be traveling faster than 1,525 ft/s for it to have more than a 50% chance of breaking through the armor panel.

When you say that the vests were designed to stop rifle rounds, that is not entirely accurate. The majority of the vest will only stop a handful of types of small arms fire, any hits by a rifle round will absoultey penetrate. This is where small arms protective inserts or SAPI plates arerequired. Due to their weight and bulk (although they have become tremendously less bulky since the days of the (RBA) Steel and Ceramic plates were originally only being attached to protect critical organs, mainly the chest, neck, and C-spine. This was done mainly as an effort to make such injuries simply survivable or as close as could be expected.

A couple things that need to be cleared up.
To answer your question, as well as correct your assumption regarding what the vests were designed to stop, of the two different varieties of SAPI plates that have been issued as part of the Interceptor armor system (more on teh second in a minute), they were in fact both required to be rated to stop, shatter, and catch any and all fragments from the 7.62 x 51 (.308) round with a muzzle velocity of up to 2,750 fps (Since the ballistics of the 30-06 are nearly identical to the .308 in which it was the precursor, and since it is no long a common Military nor NATO caliber the actual ballistics are not included.

while the original Interceptor model with plates was only able to protect the solider from rifle wounds that were taken head on to COM, it became clear with the advent of large scale IED and sharpnel attacks as well as the more gueirlla style tactics being implemented, that many soliders were suffering more serious wounds both from large shrapnel injuries that would sever large arties in less vital areas such as the groin or upper arm, as well as the danger of recieving fire through the exposed areas such as the armit when actively engaging the enemy with a weapon (these under the armpit style wounds were the exact same problem that were responsible for the lives of many police officers even while wearing vests and have since led to a sorty of reversaal in training from the isoceleces shooting position which prsents the thinnist part of the body to the shooter back to the weaver style stance in which the shooter is engaged head on in the belief that any incoming rounds will hopfeully strike the body armor head on.

As a result the .mil quickly began to press into sevice the ESAPI plates, these plates included deltoid and axillar protection, as well as Enhanced side ballistic insterts ESBI.

This increase in protection extending down from the neck through the chest and down below the groin and thighs, as well as securing the lateral sections of the soliders body, dramatically began to cut down on critical injuries due to massive shrapnel wounds from IEDS and made such attacks much more survivable. The upgraded armor also had the added benefit of now being able to survive direct hits from 7.62mm m2 AP and API (armor piercing and AP/incidinary rounds.

So long story short. Is it survivable, hypothetically yest it could be survived. Does it have just about as good a chance as killing you given the range and larege caliber of ammunition, yes probably.

Will it definitely definitely feel like you just got tthe absolute shit pummeled out of you by an 800 pound sledgehammer, which will almost certainly fracture the majority of bones in your chest or ribs, and could then perhaps collapse a lung, rupture a vital organ or stop your heart all due to sudden blunt force trama. Ya, its definately possible.

Remember the ultimate goal of these types of armor advancements is to simply work to keep the patient alive usually for what is knwon as the 'golden hour' at which point they can hopefully be already recieving true medical treatment. Do plenty of guys get dinged in the chest by an AK and come out without even a bruise and are immediately still combat effective, sure, plenty. But not everyone.