I have a sig Sauer m400 and currently it has an eotech xps2-0 and a magpul buis with an f marked front sight base. Im trying to determine my best method and distance to zero my ar with these two sighting systems. I will say that I have a Gisele ssa-e trigger and ive shot this rifle with a scope and have gotten sub moa groups out of it at distance so I know it’s an accurate reliable rifle. Please weigh in with your opinions cause in really curios to hear your train of thought. Currently the rifle is zeroed at 25 meters. My max range to use this rifle at is a 300 yard bay at my local range. I zero off a set of sandbags that I use to shoot my target rifles with so I can remove as much of my error as possible. Is that a bad method because I don’t have free float handguards? In just curious to hear everyone’s opinion.

There are lots of opinions on the subject.  Personally, if I'm using a magnified scope i sight it for 100 yards.   With a non-magnified optic (like the EoTech) I would zero at 50 yards which provide a nice flat trajectory from 50 to 200 yards.

This is the way to go. But I would zero the iron sights at 25 meters, so the bull will be bad zeroed at 300 meters

Look at this, then decide.



I decided 50 is the way for me except for my long range guns or with an ACOG, then it's 100.



For you with an EOTech you might also agree on 50.







 

I mostly shoot 200 yards and under because of the ranges available where I live.  So I like the 50 yard zero for irons or non-magnified optics on my carbine.  Any range I'm likely to shoot at I'll be close to zero.

thanks for the info guys! I will defiantly be zeroing for 50 yards. i guess the only question that remains is should i zero from bags or not? i think i should zero from bags so i can remove as much shooter error from my zero as i possibly can. this should provide me a larger margin of error at the target shooting offhand shouldn't it? please someone tell me their opinion of this.

Yes, do your zero from the most stable condition you can.  

If you use bags or a shooting rest at front and bag at the back, give thought to the fact that your barrel is not free floated.  Pressure on your forestock can alter your point of impact..  

Try not to push down on the bag or rest.  Just let the rifle lightly rest and try to use the exact same location as where you will place your support hand when shooting.  For precision shooting with your scope and to take maximum advantage of that trigger, consider adding a free float rail.  I did with the SSA-E and it made a difference.  Not just in group size, but in POI shift.  

With a regular handguard, I was seeing as much as 4" shift at 100 yards, depending on how I either held the rifle or set it in the bags or front rest.  Using a bipod had a completely different POI, close to 6" away, depending on whether it was preloaded and by how much pressure.  A free float rail eliminates all of this variation.

thanks for this input I really appreciate these data points from those who have learned the hard way so i dont have to learn the hard way. What rail would you recommend to someone like me who has a pretty bone stock ar-15?

100 yards.

Very good replies so far but here is another tool for your tool box:

I have found that sighting in 2.5 inches high at 100 yards gives me the most useful zero.  This is roughly a 265 yard zero with M855.

You are only 1 inch low at 25 yards, never more than 3.25 inches high occuring at 75 yards, 3 inches low at 300.

At 400 hundred you are 16 inches low.  By aiming at the top of the head of an average humanoid target, you will drop it center mass.

From 0 to 300 yards this system in basically point and shoot.  Very useful for sighting systems that are not easily/quickly field adjustable.

By resting the rifle on the magazine with your hand grasping the receiver in front of the magazine you will minimize pressure affects on the barrel sans a free float.

What you said, look at the 50 yard zero graph above. Zero at 50 and you have basically the same thing and it much easier to accurately sight in at the closer 50 yard target than it is to sight in 2.5 high at 100.



But do it however you like, just sayin'.



 

50 yard zero for me, I find it faster and easier to zero my rifle by shooting at 25 yards first and then confirm at 50. I use this target.

and use bags, it's best to illuminate as much shooter error as possible.




ETA: got the target from here.

This what mine is at.

100 yds for a magnified optic and 50 for a red dot.

The drop is 2" plus or minus from 50 yds to 200 yds with M193.  M855 is even worse.
You can't hold a red dot to that kind of tolerance at 200 yds.

I guess that's a way to justify the 50 over the 100...

I prefer the 100 over the 50 because everything is a holdover at distance, less to worry about under stress.

Both are good zeros.