I have my 16" carbine sighted in with the PPU M193 clone. I also have a bunch of ADI with the 69gr SMK that I've been saving for a rainy day and it shoots the same as the PPU. Today I decided to use up a lone box of PMC X-Tac M855 and found that it shoots the same also. I've verified the zero on all these types at 50yds and at 160yds(farthest I can shoot at my local range)and they all fall into the same spot.

Not complaining here but I was wondering if what I've experienced is common or if I'm just lucky. The clone of the rifle I was using today shoots all three the same, but it should since they have identical barrels. I've had other rifles shoot multiple loads somewhat close but never like this. I supposed if I push the ammo past 160yds the differences will start showing up but for what these rifles are set up for I doubt I'd ever go past 200yds.

I would say that's pretty lucky!
I successfully developed a load that matches POI and velocity as a factory load, which was a good day, but I'd go out and buy a lotto ticket if I were you.

I would say go buy a lottery ticket, you are lucky.
Every rifle I shoot, there is always a POA-POI shift when I change ammo. Even ammo with the same bullet weights, but different brands.
I have had mild shifts (1/4 to 1/2 moa in any direction possible) up to as much as 2 moa shifts (in any direction possible).
I have had the rifle zeroed to one ammo, switched to different ammo, and had it shoot 2 inches high and 2 inches left! I switch back and it hits dead center.
Very annoying.

Pretty much you have to test every ammo you plan on shooting and know how much, if any, the POI shift is and take note.

I typically don’t notice any shifts or change in POI with my ARs out to 100 yards with 55-75 gr ammo.

I've never noticed much of a shift with ARs.

Outside of ARs:

Changing the bullet weight seems to generally cause the biggest shift of all.  Changing the bullet type but keeping the same weight (soft point vs. FMJ) is a lesser effect.  Much lesser would be switching between brands of the same type like US vs. Greek .30-06.  

I'm running ballistic advantage barrels and I pretty much shoot what I can get my hands on for a decent price.  Lately my shooting has been with a mix of Frontier M193, Federal M193, Frontier 55gr HP, Norma 55gr ball, and a mix of 62gr stuff, and it all goes to the same place.  The only one that doesn't is wolf 55gr.  It shoots a little high and to the right, but within a MOA or 2.