3 shots into 6" is pretty terrible (but you knew that already ;-). With such bad results, you ought to be able to isolate the culprit pretty quickly.
It is possible that that ammo is simply that bad in your rifle. Try some other ammo, preferably "better" ammo. BTW IVI military ammo is pretty good (I haven't heard of IVI 223 match but I would assume it would be as good or better than the regular service grade ammo). IVI will shoot 2.5" groups (5-10 shots), or better; some even say it can shoot 1". FWIW I think 62 military ball ammo will shoot quite well out of a 1-9" twist barrel.
Another possible reason is a serious flaw in your sighting system - check to make sure your rings and bases are tight (see if you can wiggle them). Also possible is that your scope is moving internally. If you have not previously shot good groups with this scope (on this rifle or on any other), it is potentially guilty until proven innocent. Doesn't matter if it is a $200 scope or a $1500 scope, no scope can be fully trusted, ever; be sure to always include the scope in your list of possible culprits. If you have another scope available that you can swap into this rifle, or if you have another rifle available to swap this scope on to, you can test that.
Make sure your two action bedding screws (stock screws) are good and snug. They don't need to be (and should not be) crazy-tight, but they do need to be firmly tightened. If you have never taken your rifle's action out of the stock, now might be a good time to - remove both screws and take out the action. If it is covered in oil/cleaning solvent, this needs to be wiped off as well as possible (also clean the inside of the stock).