Range to zero dual optic: 4x scope & Red-Dot?

[Dochartaigh]

I'm running a dual-optic setup on my 16" M4 and wanted suggestions on how to zero each sight. It's a Leatherwood CMR 1-4x scope (usually set on 4x), and a Trijicon RMR red-dot (which is 1x) mounted a little higher, and to the right of the 4x scope. Here's what the setup looks like:



I wanted a dual-optic setup because I'm not the best shot at/past 100 yards without magnification, and when the scope is set to 1x, it really isn't a true 1x and kinda stinks close-up (especially when I was used to my old Aimpoint-style optic which is truly 1x and a pleasure to use up-close).

So ideally I'm looking for the 4x scope to be zeroed at 100 yards (which it currently is, and I can read the pre-set reticle markings on it to hit further than that), and have the Trijicon RMR red-dot to be zeroed at ranges commonly found inside a house, maybe to 50 yards max.

I was thinking of zeroing the red-dot at 25 yards, but am worried that I'll have to aim quite a lot low to hit something inside the house (my ballistics calculator says that with a 25 yard zero I would have to adjust the sight up 35 MOA to hit 7 yards/~20 feet; I don't know how many inches difference that would be, does anybody have the formula to calculate this?), and to hit 50 yards I would have to go down ~7 MOA to hit 50 yards which isn't nearly as large of a difference so that's probably fine. Would this setup also have the bullet drastically move to the left at further ranges as well, since the red-dot is off center bore (granted I can tilt the rifle, but this setup is ideally meant to be used without having to do that)?

Any suggestions?

[Ranger P229]

Here is a chart for a 223 zeroed at 25 yards. I don't know the specifics of your load, but this is good for the sake of example.

52 SIERRA BTHP .224 .234 2.50
Range Drop Velocity Energy Flight Time

0 -2.50 3000 1039 0.0000000
25 0.00 2894 967 0.0255875
50 2.24 2791 900 0.0518819
75 4.21 2689 835 0.0794466
100 5.89 2590 775 0.1078010
125 7.24 2493 718 0.1373987
150 8.27 2399 665 0.1680107
175 8.91 2307 615 0.2000126
200 9.18 2218 568 0.2331056
225 9.04 2132 525 0.2673009
250 8.39 2047 484 0.3034837
275 7.25 1965 446 0.3408954
300 5.61 1886 411 0.3795376

As you can see, you only have a 2.5 inch difference between 0 yards and 25. So hold 2 inches high on your target for POI to be the same as your dot when shooting across the livingroom.

Could the number of adjustments be due to the range? 4 clicks/inch at 100, 8 at 50 etc. I can see how it would call for dozens of adjustments at 7 yards.

I wouldn't worry about that 2.5 inches at 7 yards. Aim for center mass and you're good to go.

[Dochartaigh]

Thanks for the info. I'm running Lake City M855 62grain green penetrator tips (which I should probably buy a mag of something that won't go through my house and into the neighbors for home defense).

If my memory serves the Trijicon red-dot is 3.715" above boreline, which is pretty drastic; your numbers seem to be for 2.5" above? So even if the bullet is ~4" high at inside-the-house ranges, that should be perfectly adequate.

Any thoughts on the red-dot being mounted to the right side, and when I shoot at say 50 yards (with a 25 yard zero), is that going to make the bullet impact quite a bit left?

[aubie515]

IMO, your set up is way too heavy for HD use. I had the CMR...I liked the reticle since it can be used for 62gr 223 along with 168gr 308...biggest knock on that optic is that the knobs move way too freely.

I had recently sold my RMR as well...if it was me...anything I buy from Trjicon is not going to require batteries. Think murphy's law...your RMR uses batteries and it can die on you when you need to rely on the optic...inside of your house...if your CMR is on 4x and RMR batteries die on you...you are SOL carrying a heavy rifle.

M855 is a poor choice for HD as well...there are plenty of good choices for HD.

I don't know what ballistics program you are using but that doesn't sound right to me...35MOA is roughly 35" at 100 yards.

If this was my set up...I'd zero the RMR at 50 yards and call it a day...the CMR I'd have set at 100 yards since the reticle has hash marks for hold over.

[Dochartaigh]

Any suggestions for 5.56/.223 for home defense? Honestly, I would probably grab my Remington 870 if anything were to happen in my house, but when I would like a light on my gun for that (as like most people I sleep with the lights turned off), the M4 has one, where the 870 currently doesn't. ...just want to get all options setup properly, and know where my bullet is going to hit with a certain zero at a particular range on the red-dot since I'm a little new to zeroing and MOA and such.

My M4 weighs in at 9.35 pounds with the dual optic setup which I don't think is overkill in the weight department for me (I'm a big guy). My 870 weighs around 8 pounds for comparison, with no light, or optic.

I wanted the RMR with adjustable (battery powered) brightness as I had a Trijicon TriPower before, and with that scope, when I was only using the (larger than the RMR) fiber optic light gatherer (and tritium), it just wasn't bright enough especially when aiming into a brighter lit area, or when I use my flashlight it washes out the reticle so it's unusable; so needless to say I didn't want the fiber-optic (non battery powered) RMR version (which most people's reviews also mention those large problems with the non-powered version). Regardless, the M4 has the 1-4x scope (with etched/black reticle for daytime use along with battery illuminated reticle as well), a RMR with a 4-year battery life (which I plan on changing the battery on my birthday every year just in case), and even have Troy flip-up tritium sights...so no matter what I have a sighting system that will work regardless of electronics.

I'm using the "Shooter" ballistic program for Android phones (very highly rated, although that might not mean anything), and with a 25 yard zero, for 7 yard (inside house ranges) it says to adjust it up 35.3 MOA, which although that seems like a lot of MOA, at 7 yards it seems to be only inches.