There's so much good info on this site that I run the risk of overthinking this.  So instead of asking a bunch unnecessarily technical questions, I thought I'd ask instead: What matters and what doesn't?

I have an LE6920 I'd like to shoot recreationally at 100+ yds and possibly for home defense once I get comfortable with it.  I have it hitting a couple inches below POA at my local 25 yd indoor range which (I think) will get me on paper when zeroing at a 100 yd range (correct?)  At this point do I need any hyper-precise milspec tactical zeroing targets?  I have some Hornady 75gr and some PMC M193 and M855 clones.  Should I just use these or choose my defensive ammo before zeroing?  My limited ballistics research indicates ammo varies less at 100 yds than my ability does :)

Any other advice for a newbie before I make the 2 hour drive?

Many thanks.

Probably going to be pretty low at 100, but youll be fine.

Different ammo may or may not shift some, but at the end of the day it wont make much difference unless you shoot specifically one load and are trying to be accurate.

Any target will work. I mostly use just a plain black dot on a 8x11 sheet of paper.  Make the dot whatever size you need to see it well.

Long as I'm starting within like 5 inches (might use 8x11 printed targets) I'm happy :)  My understanding was that the impact will "rise" out to around 100 yds, so I thought I'd start a couple inches low at 25 yds.  Am I doing it wrong?

Thanks again.

You can print out these to give you a pretty close 100yd zero at 25yds. Still a good idea to verify at the actual range.

http://arma-dynamics.com/assets/red-dot-25yd100-mod1_1-(ar-15).pdf

Not really.  It doesn't matter much.

Your sight offset is what you are starting with.  So with irons it might be that your sights are about 1.5" above your bore.  If you're shooting 2" low at 25 yards, that would mean you lost a half inch at 25 yards, implying you would hit about 2" low at 100.

Gravity of course comes into play, but not a whole lot at these distances.

To keep it simple, assume a bullet never rises.  Your barrel is just pointed higher to get more of a 'lob' out of it and increase the arc/range.  So you start with your sight offset and work from there.

You're ok. 100 yds zero point of impact at 25 yds should be a spit more than 1.5" lower than your point of aim For example aiming at dead center on a 25 yd target, you'll want the point of impact to be approx 1.5" beneath that for a 100 yd zero.  Make sure you go somewhere that will give you a 100 yds firing distance so that you can verify. Unless you are shooting for extreme accuracy, you'll be surprised how little adjustment will be needed once you verify at 100 yds with all things being same same. If so desired, you can always take a plain jane target and draw 1" grid squares or whatever dimension you like. I like the 12" x 18" splatter targets that have the 1" grids such as these: http://www.ebay.com/itm/10-25-50Pack-12x18-Sight-In-Splatterburst-Target-Burst-Bright-Florescent-Yellow/252955305430?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160727114228%26meid%3D9617eb7a902b4eea81bc6e7b8a1bb8cf%26pid%3D100290%26rk%3D2%26rkt%3D4%26sd%3D172159560876&_trksid=p2060778.c100290.m3507

Do you know how to adjust the optic, hard sight, etc you plan on using? A lot of people have a brain fart with MOA adjustments, etc. No biggie though. We're all here to learn and help others.

The example I gave you is using a basic 55gr bullet with a sight 2.5" above bore. Pretty generic but close enough. Let us know what you'll be using for sighting and ammunition so that we can adjust your point of aim if needed.

Do a google sear for "free M4 zeroing target" and print it out. Its designed for 25 meter 300 meter zero of the M4 carbine. Place it at 25 yards and zero your rifle. It will get you on target at 25 and 300 yards and will be 1.6" high at 100 yards, still puts you on target with irons and all you need to domis compensate poa for bullseye hits. If you are setting up a scope(which I would suggest for 100+ yards) then zero the scope at 100 yards.
Ammo will be the biggest factor all otner things being equal. Cheap ammo will never group well.  Find a good match or hunting round that your barrel likes and use that load for your long range shooting, if you are juat ringing steel or punching paper any ammo will do.

Here's how I zero a new firearm. I start off at 50 yards. Pick up a Ross brand 20"x 30" White Foam Board or 2. I get them at Walmart for just under $1 each. Then I'll use Shoot N C reactive targets. Put three 6" targets across the upper part, then four 3" across the middle, and then a row of 2" across the bottom of the foam board. From a rest, using irons, I zero in the 6", then the 3" and then down to the 2". At 100 yards, I'll start with an 8" and work down to a 6". My 59 year old eyes can't see a 3" target at 100 yards. 

FWIW...

step 1  start at 25 meters irons only

step 2 zero again at 100 irons only

step3  NEVER ALTER IRONS AGAIN

step 4 get a red dot with an absolute co witness mount. put dot on top of FSP as you shoot.  the gun

fine tune it at 100 meters.

in theory if every thing is perfect & you start at mechanical zero , if you memorize your up down left right on milspec irons all milspec guns will require the same steps(number of turns to irons. ) to zero the irons.

but the best answer I have found is buy an 4X acog zero it at 100 meters & you will find yourself on target out to 400 meters on steel silhouettes all day long.

just never take it off.

No. The reason a rifle's sights need zeroed is because each rifle is slightly different. One FSB may lean right, another may lean left, one front sight post may be tall, another may be short etc. for dozens of parts and ammunition. Now, everyone's zero on a rifle could be slightly different from the way they line up the sights, the way they hold the rifle, the way they pull the trigger, and follow through. This has nothing to do with rifle to rifle consistency. This also has nothing to do with mechanical zero. A rifle being zeroed at mechanical zero is only luck.

I shoot irons-only most of the time with a carry handle, and this is what I do. For a target I use a paper plate with a black circle  roughly the size of a dime at 25 yards.

I specified "milspec - the army teaches if you take a  rack  a2rifel set the sights  to mechanical zero then write down/memorize the alteration you  need to get it zeroed. that any other a2 rifle you pick up you can set it to mechanical zero go through your memorized zeroing procedure & it should be zeroed for you. "

I stated this is a theory.

That's misinformation, even if the Army teaches it.

Yeah the Army is dead wrong on that shit!! Each rifle is going to different when in regards to windage/elevation clicks, that number you're thinking of is when you use the same rifle after someone else zeroed it to their adjustments.

William

Important thing is to shoot a group - 3 or 5 shots, ignore the hole and just keep aiming at the same spot. And only then adjust sights/scope.  Then shoot group again.

I've seen so many shooters go through 20-40 rounds firing a single shot, changing sights/scope, firing a single shot.  They are actually shooting a 4" or so group, and chasing single shots all around.  This method works, but only if you know the rifle, ammo, sights, and *you* can shoot very small groups.

"... I have some Hornady 75gr and some PMC M193 and M855 clones...."

55gr and 77gr will usually have different 100 yard zeros

it's real hard to see .22 holes on paper at 100yrds  ( try to beg/borrow/steal/ buy a decent spotting scope)

also, anything you zero at 100 will be way off at living room distances, because the sights on an AR sit up higher - offset

just practice, and learn to deal with it.

have fun with it.

Two hour drive status?

Welcome.    My suggestions would be:

Read a lot of the articles on AR15.com.  They are a good source of info after you sort out the BS.

These are two good sources about zeroing.  RIBZ and Combat zero

Google JBM ballistics and learn to use their ballistics spreadsheet.     It's just a fill in the blanks questionnaire.     My experience has shown it to be highly accurate.

There are a lot of different ammo manufactures out there.     Some good, some not.    Pick one that works for you and stay with it.    Before I learned about ammo, I stock piled a lot of cheap stuff, which I now know to be not very accurate.   Today, I'm buying Federal American Eagle.  It suits my needs

Look on YouTube for Sniper101.  He has published a lot of videos about virtually every aspect of shooting.   Jump start your learning curve.

Good luck

First of all, what kind of sight? For open sights at 100, I like a 6-12" black bullseye at 100 as an aiming point. For a 2 MOA red dot, I like a 4-6" bullseye.  With a magnified optic, I like a hollow bullseye with a 1" white bullseye.

For height below bullseye at 25 yds, try JBM Ballistics web site. Basically, you want to be 1" low at 25 yds and perfectly centered horizontally to be on target at 100 yds.

You can get pretty close by pulling your bolt and looking down the bore at the bullseye and adjust the sights to the bullseye. It works!

For a red dot, I sight it in to 1" high at 100yds or dead on at 50 yds.

For open sights, I sight in dead on at 50 yds too. I shoot at 100 + to confirm horizontal zero.