I'm a newb with military optics. Just got a TA33-C-400129 green horseshoe. Would like to zero at 50 yrds as I live in a urban environment and won't be shooting much past 100yrds. Should I start at 25? 55 or 62 gr or won't it matter?  It's on a 6920. Thanks.

if you arent zero-ing it how its intended, it doesnt matter what grain bullet you use as the BDC wont be accurate anyway.

You can start at 25 to make sure you are on paper, but I can almost always get on paper just by removing the upper, and bore sighting it before hand to save time. So I always start at 50

Ok, I've been down this road and I'll tell you the technically correct answer and the real answer. Your BDC is calibrated for a specific grain round with a specific BC for a specific HOB and MV, if you use any other ammo/rifle and in different atmospheric conditions it will deviate and be incorrect. That's the technically correct answer.

In real life using ball ammo from a rack grade rifle, the above differences won't matter at any realistic ranges. Now, if you're shooting some precision setup at 600m for groups or something, then yeah it matters, but you probably shouldn't be using an ACOG for that either. People freak out about using 55 vs 62 when they're shooting at silhouettes at <300m mostly, and for that you'll be fine. I use my 31F with a 12.5" SBR shooting 77gr to 300m, and I've never noticed any difference. This is likely a lot larger difference than you'll use, and you'll likely notice even less than I do (none).

As to zeroing, why would you not just zero it as designed? I guess you could zero the dot at 50m, but it dicks up all the rest of the reticle. I'd just zero the dot at 100m as prescribed, and use it as intended. If you're doing a rough zero at 25m, you'll want to zero POI to the 300m hold. This is the Army method of getting a rough zero, and will get you on paper at 100m, where you'll of course want to confirm.

Lastly, if you're really worried about any trajectory differences, zero 1" or so high at 100m. This splits the difference of a less efficient round (the M855 by published BC/MV (and thus what Trijicon calibrates for) is usually more efficient than most rounds I've used), thus if I shoot from 0-300m, I usually end up about +1.5"@100m, dead on at 200m, and -1.5"@300m. This is subjective, but I find that more useful than dead on at 100m, -2"@200m, and -5"@300m. I'm making these exact numbers up, but hopefully it illustrates the purpose.

I know were the 300m hold is with a chevron, where is it with a horseshoe/dot?

The tip of the BDC post is the same 300m hold on both. On the chevron, people say to aim with the end of the legs as the 300m, but if you look the end of the legs is actually at the same level as the tip of the post as well.

So I aim at the top of the vertical green bar?  I see now. What an awesome optic. I can.t wait to shoot this thing

The horseshoe dot is my favorite ACOG.   Use an M193 equivalent.

If you want a 50 yard zero, zero it to shoot to the top of the dot at 100.  That will put you right behind the dot at 50 and a little past 200.   You should be dead on at 300 and 400 M.  Pretty versatile optic huh?

This is correct, and yes ACOGs are great, as is the horseshoe. It's a great all around reticle. I have used lots, and while I mostly own chevron currently, the horseshoe is a great all around reticle.

So I made it out to my property, was going to sight in Sat. but my eye swelled nearly shut from Blepharitis, had to pack up and come home, this really sucks. I'll head back out when this clears up.

Hey nice rifle OP looks pretty simple I am thinking about putting one like that together

Finally got out to sight in, got on paper at 30M, then moved to 50 yrds. Was 2" left, elevation is right where I want it at 50 I will leave that alone, had to give it quite a few clicks(12+) to move right.  Next time out i'll set up at 100 yds, should be right on. Using IMI 55gr.  Thanks

Good looking rifle, and a great optic


Here's mine: