Piggy-back RDS Zero Range

[Trigger Monkey]

When I mounted an RDS at 12 o'clock on my SPRecce my first instinct was to zero it at 50 yards the same as my other red dots but I ran the math and realized that probably wasn't ideal for what I wanted. 0-50 yards things looked fine but after that the increased height over bore meant I'd be holding pretty low for 100-200 yard targets, which could be small pepper poppers or gongs. Below is 50 yd zero with 4.6" HOB, red being the hold point and the green circle being the approximate impact area.

Running the numbers for a 25 and 36 yard zero revealed they were pretty horrendous options:

I ended up settling on a 100 yard zero which coincidentally works out close to the same holds as a 50 yard zero that I would typically use with offset sights and lower 1/3 RDS mounts. Below are my holds using the 100 yard zero with a 4.6" HOB, zeroed with pretty standard 55gr ball, however under 200 yards it works pretty much the same with IMI 77 Razor Core.

Like most things it's going to come down to how you intend to use the RDS, if one doesn't perceive ever having the need to engage anything farther than the zero distance then go with God. I view the RDS as an alternate sighting system so I want it to be capable basically from 0-300 yards and why I went the way I did.

What distance are others zeroing their piggy back red dot?

 

[Emerson0311]

When I mounted an RDS at 12 o'clock on my SPRecce my first instinct was to zero it at 50 yards the same as my other red dots but I ran the math and realized that probably wasn't ideal for what I wanted. 0-50 yards things looked fine but after that the increased height over bore meant I'd be holding pretty low for 100-200 yard targets, which could be small pepper poppers or gongs. Below is 50 yd zero with 4.6" HOB, red being the hold point and the green circle being the approximate impact area.
View attachment 8524192

Running the numbers for a 25 and 36 yard zero revealed they were pretty horrendous options:

View attachment 8524202

I ended up settling on a 100 yard zero which coincidentally works out close to the same holds as a 50 yard zero that I would typically use with offset sights and lower 1/3 RDS mounts. Below are my holds using the 100 yard zero with a 4.6" HOB, zeroed with pretty standard 55gr ball, however under 200 yards it works pretty much the same with IMI 77 Razor Core.

View attachment 8524190

Like most things it's going to come down to how you intend to use the RDS, if one doesn't perceive ever having the need to engage anything farther than the zero distance then go with God. I view the RDS as an alternate sighting system so I want it to be capable basically from 0-300 yards and why I went the way I did.

What distance are others zeroing their piggy back red dot?

Same as the rifle zero distance.

 

[TonyAngel]

I run a piggyback with my ACOG and I use it solely for up close, so I zero it for 50 yards. Anything beyond that, im using the ACOG. Actually, I use the ACOG at 25 and out most of the time.

 

[Jack_L]

100, but I could argue for 200 given a specific use case.
The 100 yard zero, like with “normal” optic heights, gives the most gradual slope toward the zero distance and works mostly off of hold-overs. 100 yard/meter zero also tends to give the most solid zero with less sensitivity to error due to imprecise range to target when zeroing.

200 makes a case when being used primarily as a passive night vision aiming method when also integrating a laser zeroed at 200. That’s a different discussion, but the system as a whole matters.

 

[Jack_L]

I run a piggyback with my ACOG and I use it solely for up close, so I zero it for 50 yards. Anything beyond that, im using the ACOG. Actually, I use the ACOG at 25 and out most of the time.

That’s actually kind of making things harder for you, as the more aggressive slope of trajectory with the 12:00 dot requires different offset holds at close range. My note does tend toward use based on small target sizes, so your requirements could be different than mine, and likewise your satisfaction may not change based on mine.

 

[FatBoy]

I run a piggyback with my ACOG and I use it solely for up close, so I zero it for 50 yards. Anything beyond that, im using the ACOG. Actually, I use the ACOG at 25 and out most of the time.

I do the same with my ACOG and my LPVOs. I zero the RMRs at 15 yards and it gets used for pistol distances and anything 25 and out or small (2” swingers) I use the optic. Not saying it’s right, but it seems to work. I recognize I have no idea what my holds are past 25 yards. I should probably work in that…

I’ve been considering trying a 100y zero on the red dot and seeing if it makes any difference or easier.

 

[DM1975]

I have a piggyback red dot on my 1-6x on an AR. The 1-6x is zeroed at 60-200 but the rds is zeroed at 100 yards for passive night vision use. With HOB of 4.5” zeroing it the same at the LPVO gave too drastic of a change for me and the 100 yards zero was the flattest I found.

 

[Burdy]

My LPVO is at 50 yard zero, piggyback is at 100 yard zero. I want the smallest amount of variation from 0-100 on the RDS and I want to be able to hold dead on at my farthest RDS distance since it will be visually difficult to determine hold under/overs with 1x. My HOB is 4" however using a 1.25 LPVO mount. YMMV.

Not coincidentally, that HOB is also exactly an EXPS3 on a Yagerworks XPS A1 mount. I want everything to be the same when I pick up any gun of my own.

 

[Trigger Monkey]

While researching this topic a little more I came across a guntuber (I know, dangerous territory) that was advocating a 75 yard zero for piggyback red dots, and it was intriguing so I ran some numbers. When looking at it from a pure numbers perspective it makes a compelling argument as the way to go since it has a low max. ord. and a pretty decent far zero range. However, when I compared it visually to a 100 yard zero on an 8" popper the differences really seem kind of negligible up to 200 yards and probably a bit beyond that. All in all, I'll be sticking with a 100 yard zero on the 12 o'clock mounted RDS for simplicity and it's still effective to practical ranges in my experience thus far.