I shoot 3 gun and most of us use a 200 yard zero. That will take care of most targets to 250 yards. At 300 to 350 I put the dot on the upper chest or the head on the front post if I am using standard sights.

I assume you obtained this gun for both defensive and hunting purposes. In the Army we usually zero to 50 yds! Zeroing for a headshot on a siloet target at 50 yds is equivalent to a chest shot on average at around 500yds with a .223/.556 armalite style rifle.
Not to mention it is much more simple of a task to zero at 50 yds rather than 100, more ammo saved as well! Place 1 shot using a sled or bi-pod for center mass of your target. Once your shot has been placed," reguardless of where you shot landed on the grid" keep you rifle still and adjust your optic or apertures to the hole left by the previous shot. This should ensure that you have either nearly or completely honed in your sights in 1-2 shots! Best of luck my friend! Hooah and rock steady!

100 yards

100 yards.

Sight at 50 yrds. It'll be zeroed in there and at 225 yrds due to bullet drop.
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At 1/4 inch low at 50 yards. you should be good from 25 to 100+ yards. without any hold over or under. Assuming you are shooting 55gr bullets and your rifle groups decent.

Zero at 100 yards. That should cover you up to 300 yards.

I'd set at 75 yards. We go out every weekend just for plinking. It's prefect. Short to semi range. Trust me.

If the range you are using is only 25 yards long, then you could sight it to be about an inch low at 25 yards, which will get you close to a 50/200 yard zero.

The typical answer would be to site the weapon in at 100 yards. However, given the fact your primary purpose would be for plinking, and assuming this would be at shorter ranges (ie 50 yards or less), I would just site the weapon in at 50 yards as Steven H suggested. If the purpose of the weapon changes, I would site it in at 100 yards. Thanks.

Common wisdom is to start at 50 years. Once you get it good and tight, move out to one hundred yards. Anything over that you are starting to compensate for drop.