M*CARBO Brotherhood

Can't mount optic to MCARBO optic mount

Feeling like a dummy here.

My Sig Sauer Romeo5XDR just showed up, and I’m trying to mount it to the rail on my M*CARBO optic mount. I removed the little screw and plate thingy on the optic’s base. But the optic just…won’t go onto the rail.

If I try mounting the optic on the rail on the rifle itself, it goes on fine – drops right on, no need to force it at all.

Below is a photo of as close as I can get it with the MCARBO mount. I can’t get it to sit flush at all. (Photo isn’t great, but I had a hard time getting a good angle.)

Any suggestions? Am I overlooking something super obvious?


That block showing on the bottom of the pic rail should fit PERFECTLY in the gaps on the rail.

Try a mm forward or backward until it drops in. Then tighten 5he clamps onto the points of the rail.


Thanks for the reply, @Dred.

That’s how it feels with the rail on the rifle (i.e., the block is a perfect fit).

With the slots on the MCARBO mount, it just didn’t want to go in. I spent at least half an hour trying to wiggle it “just so” in order to get it to fit, but no luck. Eventually I just applied a bit more force, and it went in. But there were grinding sounds involved, and I’m not sure it’s ever coming back off. :sweat_smile:


I’m not sure I understand why it won’t fit but, I remember sliding mine on from one end . Not pushing them down from the top.

Both mine used Romeo 5. Don’t know if the XDR are the same.
Glad you at least got it on.

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@mp84 Can you send a picture of how it sits now? It should sit down and flush with no voids.

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@mgmargate The first two photos are with the rifle on its side with the mount in the “flipped to side” position, since that’s what allowed me to get the camera in there a little better. The last photo is with the optic actually in position.


It still looks as if it’s not sitting quite right( not flat). Have you tried loosening the screw & making sure u hold tight to the front?


Thanks for the encouragement @mgmargate.

I loosened the screw, removed the plate, and yanked really hard to remove it. (Definitely involved a moment there of “oh man I hope this doesn’t break anything…”)

I tried putting it in each of the three positions on the mount. Each time it went in, with a little less grindy-sounds than the previous time. Now it can happily slot into any of the three positions. I guess there was just some roughness on either the little block on the bottom of the optic or on the mounting slots, which has now worn off.

Thanks everybody. :slight_smile: