Compatibility of a rifle mounted RMR and a X300U positioned at 12:00?

[pangloss]

I'm finally going to the effort and expense of setting up an AR for home defense. I have a Trijicon RMR that has been just sitting around since I sold my milled G19 a few years ago, so I bought a Scalarworks 1.42" mount and put the RMR on a 16" AR with a 13.5" rail. The storm kept me from going to the range today, but just handling the rifle around the house, I think the RMR is going to be close to perfect for this role. My next decision is what kind of light get. I'm trying to decide between a Surefire Mini Scout Light Pro mounted at ~10:00-11:00 and a X300U-B mounted at 12:00 in front of the folding front sight. I think I would like the X300U the most because it just seems simpler and tidier than having a light hanging off the side of the gun. However, I worry a little bit about the light intruding into the sight picture of the RMR. If I were running a SRO or MRO or had bought a 1.57" mount, I wouldn't worry about it so much because the dot would be a bit higher. If anyone has run a RMR (or any dot with a similar height over bore) with a light at 12:00, I'd certainly appreciate knowing what you thought of it. Hopefully I'm just overthinking this.

[TWR]

https://i.postimg.cc/CLmsTf44/C55-DBD30-6734-471-F-A2-EF-8-D2-C7-A680948.jpg (https://postimg.cc/56QC8yTH)
While not the same, maybe this can give you a perspective on the height of a TLR1-HL and the irons.

[HCM]

Standard “co-witness” optics mounts on AR’s are normally approximately 1.50”.

1.42 seems low to me regardless of the X300.

I would definitely try to exchange or sell the 1.42 for a higher mount.

[HCM]

https://i.postimg.cc/CLmsTf44/C55-DBD30-6734-471-F-A2-EF-8-D2-C7-A680948.jpg (https://postimg.cc/56QC8yTH)
While not the same, maybe this can give you a perspective on the height of a TLR1-HL and the irons.

The Mossie mount height is not the same as an x300 on a continuous rail.

[pangloss]

TWR, does your light block much or the view through the dot?


Standard “co-witness” optics mounts on AR’s are normally approximately 1.50”.

1.42 seems low to me regardless of the X300.

I would definitely try to exchange or sell the 1.42 for a higher mount.

I think it's too late to exchange, but I'll keep the possibility of selling in mind. After I read your comment, I thought to check Trijicon's website. Their description of their full cowitness red dot mount states that the distance from the top of the rail to the optical axis is 1.384". Lower one-third cowitness is 1.511" for the RMR. My calipers are less than ideal for measuring optical axis, but the setup I have looks very to 1.4", which, of course, is less than the 1.5" you mentioned. These numbers would explain why my iron sights block so much of the window when I have them up. I haven't sighted in the RMR yet, so I'm hoping that situation will improve when the dot is in the right place.

I'm leaning heavily toward the rifle light now instead of the X300. That would make the height issues a non-pressing matter, and I'm surprisingly approaching gun decision fatigue.

[HCM]

TWR, does your light block much or the view through the dot?



I think it's too late to exchange, but I'll keep the possibility of selling in mind. After I read your comment, I thought to check Trijicon's website. Their description of their full cowitness red dot mount states that the distance from the top of the rail to the optical axis is 1.384". Lower one-third cowitness is 1.511" for the RMR. My calipers are less than ideal for measuring optical axis, but the setup I have looks very to 1.4", which, of course, is less than the 1.5" you mentioned. These numbers would explain why my iron sights block so much of the window when I have them up. I haven't sighted in the RMR yet, so I'm hoping that situation will improve when the dot is in the right place.

I'm leaning heavily toward the rifle light now instead of the X300. That would make the height issues a non-pressing matter, and I'm surprisingly approaching gun decision fatigue.

Forget the light. Go back to your intended purpose, home defense.

For close range use with a reflex sight such as a red dot, default to higher mounts. Cheekweld and parallax are not critical factors and higher mount gives you a more upright head position which translates into seeing more/better.

Seeing better leads to better decision making.

[TWR]

I understand the mossie mount and TLR are not the same, the same light on my KMR rail sits below the front sight too. As I stated it’s just for reference, if he can see the RMR over his sights, he should be good with the light.

I don’t have a pic with a TLR on a full rail. Do you?

[TWR]

The light does not block much view at all. The PRO is mounted lower 1/3rd so it’s not seen at all.

[archangel]

Not an RMR, or an X300, but similar setup with Insight WML and Vortex Crossfire in a lower 1/3 mount:

61667
61668

(note this is with fixed front and rear BUIS. The front sight, and little bit of the light and my thumb visible behind it, are even less obvious if you are in line with the optic, instead of looking down over the rear sight like the second picture.)

[Seven_Sicks_Two]

I don't have an RMR, but I do have a 12 o'clock mounted X300 and an Aimpoint PRO on a 10.5".

The QRP2 mount included with the Aimpoint is kinda in-between absolute and lower 1/3. I don't have issues with the light blocking FOV, but YMMV.

[pangloss]

Thanks, all. I appreciate the pictures and feedback. I went ahead and ordered the mini scout. Right now I have zero rifles with a light on them, so this will be a big improvement even if not quite as optimal some alternatives. I'll give the RMR mount that I have a try for a while, and see what I think after a bit of live fire. I'm sure the experience will be a learning curve with some significant subjective components along the way.

[mmc45414]

I bought an TLR RM-2 and have been experimenting with the placement.

61722

Just farting around in my dark basement when I had it on the bottom the barrel really did throw a shadow when you were at low ready, so I moved it to the top. I think having it on top would be OK if you had a fixed front sight base behind it, or a shorter handguard. I have a 10" handguard on order so I moved it to the rear to simulate where it will be.

61723

When you sight in on something far away you do not even notice it, but when the new handguard gets here that will give me a 45 angle option and I plan to try that.

[HCM]

I bought an TLR RM-2 and have been experimenting with the placement.

61722

Just farting around in my dark basement when I had it on the bottom the barrel really did throw a shadow when you were at low ready, so I moved it to the top. I think having it on top would be OK if you had a fixed front sight base behind it, or a shorter handguard. I have a 10" handguard on order so I moved it to the rear to simulate where it will be.

61723

When you sight in on something far away you do not even notice it, but when the new handguard gets here that will give me a 45 angle option and I plan to try that.

You don't need a new rail to mount that light at 45 degrees. I've had very good results with these:

https://www.impactweaponscomponents.com/product/thorntail-1913-offset-adaptive-light-mount/

61730

[mmc45414]

You don't need a new rail to mount that light at 45 degrees.
Yes, thank you (I think I might even have the YHM version of that around here someplace...), but I maybe didn't say what I meant. I ordered the handguard prior to mounting the light, I want to get away from the full cheese grater version and go to a slimmer and shorter M-lok that might take a little weight offa the front of the gun (so I can, you know, put a heavy light way out there...).

My current setup is OK enough for now, I at least have a light on my primary carbine (it is really not that bad on top) and I will just wait to try other options until the handguard gets here. Then I will put the longer cheese grater over onto my 26" upper that weighs as much as a small car anyway :cool:

[John Hearne]

I run an Aimpoint PRO in an absolute co-witness mount with an X-300 Ultra at 12:00. Works fine.

[RancidSumo]

Quick product plug for a cheap addition I added to my 12 o'clock X300 that made a huge difference in usability. I run an X300 in a Unity mount at 12 on my 11.5 and always had a bit of trouble reliable switching it off. Put the short ARC switches on and I can't believe how much easier it is to run. Check them out if you go with this setup.