My POI seems to shift not just vertically but also horizontally as distance changes.

meaning at 25 yards, it's almost 1/4" to the left and 2.5" below the POA - the 2.5" is normal  but the shift to the left is puzzling. At 50 yards it's closer to where it needs to be but the shift to the left is still there but at 100 yards, it's right where it needs to be. So, if it's zeroed in at 100 yards, it's off at other, shorter distances like 25 or 40 or 50 yards and not just vertically but also horizontally.
Meaning the projectile is not just rising so the POI matches the POA at a certain distance  but it is also shifting left to right until POI is the same as POA (whatever distance you zero it in)
Is that a normal occurrence?

Is that due to spin drift? Or due to different weight projectiles? I did shift between several different types plus or minus 10 grains and the horizontal shift is obvious.

Iron sights?  Scope?  Red dot optic?

Could be a scope/optic being canted a bit (or you canting the rifle if the scope/optic is level on the upper.)

The only time I've noticed something similar is with a carbine "wearing" a SUIT.  The objective lens of a SUIT is offset to the left side of center.  Sighted in POA/POI at 25 yds. the POI was about 6 to 8" off to left at 300 yds.  I sighted it in just barely left (almost not measurable at 300 yds. but it made me feel better) so that POI was 1/2" or so left of POA.  At 200, 100 and 25 yds. it was then still about 1/2" difference between POA and POI.

A half inch at 100 to 300 yds. is nothing.  At 25 yds. it only matters if I'm trying to headshoot a squirrel.

So, what kind of sighting system are you using and is it and the rifle level?

Spin drift, No. And you need to compare apples to apples, unless that's the purpose of your comparison. In which case, the short answer is they will each have a POI of their own based on whatever the sight settings of the gun.

I think it's due to a different weight used, there is some horizontal and vertical shift.

your not going to show 1 moa of spin drift at those ranges

you have a horizontal offset somewhere in your setup if constant with bullet selections, if its from different ammo, yeah its normal

This.........you won’t see spin drift that close and that dramatic......

75 gr BTHP at 100 groups left of center. Same rifle same optic, 62 Gr Hornady FMJ groups right of center.

Wind.

I used different ammo and it shifts to the right due to weight difference. Spin drift has to be much less significant than ammo difference.

I still don't really get why different velocities/weights shift horizontally as well as vertically. I thought it should only shift vertically.

First, Spin drift isn't going to be noticeable until you get longer ranges above 300 yards.

Second, you are saying you are getting 1/4th inch POI deviation at 25 yards.... SO that means you are a sub 1 MOA shooter, at 100 yards,  that is some nice shooting, you should look at the 1 MOA all day thread. https://www.ar15.com/forums/Precision-Rifles/-ARFCOM-1-MOA-ALL-DAY-LONG-Challenge-/17-51  Are your groups good enough to use that 1/4th inch as a valid data point, are they numerous enough to count as a valid data point?

Also with my bolt gun(.75 MOA reliably, check the 1 moa all day thread) hornady vmax is dead on(cuz i zero with it), but XM193 is low left  and m855 is high right. you zero with an ammo and keep that as your reliable zero, new ammo would be a new zero. Barrels "whip" and flex during firing and your zero is simply a repeatable end point when that bullet is leaving that barrel at the exact same point in time of the flexing. so even though it might flex up 5 MOA, and left 5 MOA you simply adjust your sights and you are perfect, changing ammo will change that flex/whip several ways. Different weight of bullet means different amount of flex, different speed of burn means different point in barrel during flex, AND different FPS means different exiting point of flex. EASILY changing zero.

Bullets don't fly in a perfect arch

Bravo sir.

One of the clearer explanations I've seen.

OP
Yes, it's perfectly normal for different weight rounds to group differently, both vertically AND horizontally. Once upon a time, I wondered about the horizontal shift in groups with different loads, and then I researched the physics/mechanics of it. The quoted post above sums it up.

It is not uncommon for ammunition made by different manufacturers that are loaded with the exact same bullet (for example 69 grain Sierra match king) to have different points of impact...in fact, I would expect that.  This is because manufacturers may use brass with different internal capacity, different powders, primers, load to different velocities, have different crimps applied, bullets seated to different depths, and other differences in the manufacturing process.

If I were shooting at 25 yards to test 5 different brands of 5.56 ammo that were all loaded with 69 grain Sierra match king bullets, I would expect all 5 different brands to hit within 3" or so, and that group size would expand as distance increased.

If we zero at 100 yards, and stay with one brand of ammo, I would expect different vertical dispersion between the muzzle and 100 yards simply because of the difference between the height of the optic and the bore of the rifle.  If you are correctly zeroed at 100 yards, and your ammo shoots 2-3 inches off line horizontally, then something is wrong with either the optic, the barrel, mounts, or a combination of the three.

agreed.  Spin drift is the last stop before Coriolis effect.

Even between batches of my BH 69gr SMKs, I will experience POA/POI shift up to an inch, sometimes 1.5".

More importantly than checking to see if your optic is canted, make sure you are lining it up the SAME way every time.  If you're using a grid target like a BZO, line your Y axis up with the vertical lines on the target every time, and shoot the same test.

Its a simple fix. Just shoot M193.

#M193echochamber