trying to figure out the trajectory of a 9mm 115gr. FMJHP from a 16 inch rifle sighted in at 20 yards with red dot reflex sight at 1.5 inch from center of barrel.

Thanks

You'll probably realize an additional 150-200 fps over the same loads fired in a pistol.

I wouldnt worry too much about trajectory at 20 yds. It will be fast and flat. POI will change a little with 115 to 124gr bullets but once you sight it in you can just get hits all day long.
What are you shooting with a 16" bbl?
Jim

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Science plus Art

I'am shooting a Just Right Carbine in 9mm that takes my M&P mags that's the main reason I both it (because of the M&P mags)
haven't got to shoot it yet I want to see how much it will drop at 75 yds. for raccoon's.

Not much good without a chronographed muzzle velocity.

Why don't you simply try shooting it at various ranges after getting it zero'd where you want it?

We have the same problem at our club, some people will burn 100 rounds rather than run an approximate trajectory to see where to start.

If you have no chrono, make a reasonable guess and try different MV. You'll find it makes less difference than you think within 100yds. Sight height makes the big difference.
Sighted at 20 yds, it will be below LOS to 20yd, No more than 3/4" over LOS until it recrosses LOS at 60 to 65 yds at anything from 1200 to 1500fps MV. About 1.5" low at 80yds. Trajectory falls like a rock after that.

Sighting at 15yds puts the bullet within 1.5" plus or minus out to 100yd, which is where I would want it for action pistol caliber carbine matches. Out to 100yds, just aim dead center and press.
It is no coincidence I also zero 9mm handguns at 15yds, giving me a battle zero out to 50yd. (Lower sight height)
In the heat of an action match, you want to just aim at the target, not think about "KY windage."

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I have a Hi-point 995 with open/peep sights. I dial it in at 25 yards at the indoor range at it appears to hold POA=POI as far as I can see/focus once I take it outdoors. That is with both 115gr and 124gr reloads. So I wouldn't worry too much about bullet drop until you put a scope on it or unless you have reeeealllly good vision.

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But then, what do I know?