How to zero a red dot optic on a fixed-carry handle

[JeremyK]

Now before I go too far into the weeds with this, I don't need a lecture on "why don't you just put it on a flat top upper"... I already have several flat tops with optics mounted, and I wanted to try something different with this build. That outta the way...

My most recent AR build has a C7 upper with an M68 Aimpoint fixed to the carry handle via a Tapco mount. Everything has been torqued and loctite'd so she seems pretty solid. My question is, when zeroing at 25 meters, how much is the bore to sight offset going to wreak havoc with the overall zero? Do I need to position the dot higher than desired point of impact and go from there? Any info would be appreciated.

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[Heyjoe]

I'd go 1" low poi at 25 then print some shots at 100 on a big target. I didn't see any mention of your ideal zero, so I assume you're looking for mpbr?

I cannot see why your setup would be any different than finding zero on any other long gun. Your trajectory will be greatly exaggerated, however.

 

[dogface2000]

Now before I go too far into the weeds with this, I don't need a lecture on "why don't you just put it on a flat top upper"... I already have several flat tops with optics mounted, and I wanted to try something different with this build. That outta the way...

My most recent AR build has a C7 upper with an M68 Aimpoint fixed to the carry handle via a Tapco mount. Everything has been torqued and loctite'd so she seems pretty solid. My question is, when zeroing at 25 meters, how much is the bore to sight offset going to wreak havoc with the overall zero? Do I need to position the dot higher than desired point of impact and go from there? Any info would be appreciated.

View attachment 845848 View attachment 845849

That's a super cool rig.
Zero at 50 yards then check at 25,100 and 200.
Should be reasonable out to about 250.
Inside 30 will be really low but you just have to remember and adjust.
JMO

 

[Member 53328]

Why don't you just get a flat top upper? Sorry.... I couldn't help myself. I dig the fixed carry handle and optic.

 

[arrowshooter]

With that kind of off-set you will see a pretty dramatic change before and beyond your zero. Pick a zero point then shoot at other distances so that you would get an idea of point of impact, before will be low and beyond will be high.

 

[JeremyK]

I'd go 1" low poi at 25 then print some shots at 100 on a big target. I didn't see any mention of your ideal zero, so I assume you're looking for mpbr?

I cannot see why your setup would be any different than finding zero on any other long gun. Your trajectory will be greatly exaggerated, however.

well, to be honest I zero all my rifles the furthest allowed at Safefire, which is seventy five feet, five or six feet short of a true 25 meters which is about 82 feet, I believe. I just go by how the Army had me do it; Fire three rounds, examine target, rinse lather repeat until I put six holes in a satisfactory group inside the black. I guess I'm just possibly overthinking the kind of difference the offset is really going to make.

What is MPBR?

 

[JeremyK]

That's a super cool rig.
Zero at 50 yards then check at 25,100 and 200.
Should be reasonable out to about 250.
Inside 30 will be really low but you just have to remember and adjust.
JMO

Thanks! It was... cobbled together. Had to grind off that stupid bayo lug to mount the light where I wanted it. The aimpoint I got off eBay from some military surplus store. It's beat to hell but still clear as a bell.

 

[Kruel J]

I had a similar setup at one point about 20 years ago. Sighted in at 50 yards and it was good to go.

 

[American123]

If you have a general idea of the speed of the bullet, weight, and the ballistic coefficient, you can use this to figure that out.

ShootersCalculator.com | Ballistic Trajectory Calculator

Calculates the ballistic trajectory of a bullet fired from a rifle, handgun or other firearm. Produces a ballistic trajectory chart and table that shows the drop, velocity, kinetic energy, windage, and trajectory of a bullet.

www.shooterscalculator.com

Just include the height of optic over bore, and what you plan to zero it at and it will tell you the point of impact at the different distances. You can then compare based on the results what your preferred zero will be. For me, 50 is the best, but for magnified optics that have etched holds that are based on the 100 yard zero, that is preferred.

 

[Member 34319]

Picture two lasers going straight to 25 meters 3" apart. Take the top one and angle it down to the bottom one. At 3" apart that angle is far greater than if the lasers were 0.5" apart. If your goal is to only shoot at 25 meters. You are done.

Where having an optic that far from the bore tends to screw things up is going further out with a zero at close distance.

Going back to the lasers. Now that the top laser is pointed down at the bottom laser. Point the bottom laser at the 100 yard target. Which you will notice, the laser is still in line with the 25 meter target. As it is still traveling straight. This is your bore.

Now the problem...

Since you angled the top laser (optic) down to meet the bottom laser (your bore) for a 25 meter zero. That laser stays at that angle for the 100 yard target. Which means your point of impact will be way high if you raise that angled laser up (as that laser represents your optic) to see the 100 yard target. Your top laser (optic) will now be straight with the 100 yard target, and the bottom laser will now be pointed skyward. Your impact would be much higher than you expect.