Took the AR-9 below to the range today to zero my new Sig Romeo optic. Got it zeroed with supersonic ammo first then switched to subsonic. It shot really low with the subs, to the point I had to adjust the optic 50 clicks up at about 20 yards.

Is this normal?  Anybody ever go back and forth between super and sub and have to make these adjustments?

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Not necessarily apples to apples, but my P226 shoots to the sights at 25yds with "normal" 115gr ammo, but shooting my pussycat 147gr reloads at a match they hit about 4" low at those distances.
Bottom line is yes I'd say thats normal.

Zero it with 124 grain?
That's what I do.

Good to know. Thank you. I’d say it was about 4”.

I already had to crank it up with the height over bore of that optic. Was surprised there was that big a difference.

It was 115. Should have used 124 or 147 now that you mention it. The subs were 158. I knew the difference but didn’t think the POI would be that much different.

4" at 20 yards doesn't seem excessive. Keep in mind a 158 sub is like lobbing a brick.

Easy solution is to zero your supers at the top (lollipop) of the dot and then your supers will be approx. 2" below the dot @ 20 yards (assuming 40 MOA dot). Easy enough to compensate for. Or, since you're not boarding hijacked freighters at night, just zero for your HD/range ammo and kentucky windage your subs as you giggle.

115 is at the extreme light end of commonly available 9mm loads (although hand loaders sometimes load 90 or 85 grain 9mm bullets made for .380).

158 grn is at the extreme heavy end, to the point that many gun enthusiasts are not even aware of the Fiocci 158 grn commercial load, and think 147 is the heaviest available factory ammo (although 180 grain 9mm loads are possible with hand-loading; I've done it).

The velocity variation is extreme between 115 and 158.  Your findings are not surprising.

Something with a 6-9 MOA dot, because let’s be honest, it’s a 9mm.

Or, one of the Holosun circle-dot micros. Zero with the center dot using supersonic ammo, and then figure a hold between the dot and bottom notch with the subsonic stuff.