Before Scalarworks, you had two choices in optic mounts. You could have QD, return-to-zero performance or you could have light weight. Then Scalarworks dropped the LDM or Low Drag Mount on the gun world and gave shooters a third choice: BOTH. Since their initial release of the LDM/Micro (for Aimpoint Micros and other compatible red dots), they have released a number of other mounts with the same ratcheting thumb wheel and radically skeletonized design. The LDM/CompM4 is one of the most recent and the subject of this review.
Like previous Low Drag Mounts, the LDM/CompM4 has Scalarworks’ ratcheting thumb wheel QD mechanism. The wheel has a toothed circumference kind of like a gear that interfaces with a ball detent in the mount. This adds a level of repeatability not found in a simple friction thumb wheel. The wheel drives telescoping mechanism that opens and closes a clamping surface that runs the full length of the mount.
The LDM/CompM4 is machined from 7075-T6 aluminum (an upgrade from the 6061 aluminum on my early LDM/Micro). It also features a hard anodized finish on all the aluminum parts.
There are a number of other durability enhancing features that you can’t really see with the naked eye like cold formed threading and 4140H alloy steel hardware.
Observations from Use
I think what impresses me most after having spent a lot of time with Low Drag Mounts, is that the design isn’t just something made to be different. Scalarworks didn’t just make a thumb wheel because everyone else was using levers. The ratcheting thumb wheel is a means to an end… it serves a purpose. Without it, the mount couldn’t be so compact. These mounts are often narrower than the optic they are attached to. The mechanism also couldn’t be as light as it is while also being durable without the thumb wheel. A round shape like the thumb wheel can be made both small and strong.
The radical skeletonization of these mounts is another key to their lightweight. The optic basically sits on 4 pillars of material and a bunch of nothing. As you might know, nothing weighs very little. The LDM/CompM4-LDM310 that I have (lower 1/3 co-witness) weighs just 1.49 ounces. The CompM4 in the original mount weighs in at 11.8 ounces. It weighs 9.76 ounces with the LDM/CompM4.
It is tempting to think these mounts aren’t durable or at least there seems to be a perception that lightweight can’t also be durable. Well, just like I did with the LDM/Micro, I dropped this mount directly onto the optic from shoulder height. I did this 3 times with no ill effects (accept to the finish of my CompM4 – see image below). You simply aren’t going to hurt a Low Drag Mount in normal use or even with some abuse.
I also removed and reinstalled the mount from the host rifle several times to test the return to zero performance. Just like the LDM/Micro that I tested before, there was no shift that could be detected with the LDM/CompM4. I don’t know that I have proven that there is no zero shift at all but it would seem that, if there is a shift, it is well within the margin of error in my precision shooting ability with a red dot sight. I am comfortable saying that there is no practical zero shift.
I should also note that I appreciate how easy it is to install and remove the Low Drag Mounts. Some lever equipped QD mounts require a lot of tension on the lever to truly grip the rail. This makes them annoying and sometimes even painful to remove. The LDM’s ratcheting wheel only requires the user to turn the wheel as tight as they can with their thumb. It’s easy and repeatable.
The LDM/CompM4 cantilevers the optic forward which leaves plenty of room at the rear of the upper receiver rail when mounted on an AR-15. There is more than enough room for an Aimpoint 3X magnifier or night vision device.
This mount saw well over 1000 rounds, 3 drops, several remove and reinstall cycles, and more than a few walks in the woods. It performed perfectly.
If you look at a Scalarworks LDM like this one and only see the weight reduction, you would be missing most of the point. Yes, these mounts are far lighter than any other QD mount. They are also more compact, exceedingly well made, and truly functional in that they return to zero well and are easy to use.
I am someone who happens to think Aimpoint’s factory mounts are actually very good. They work. So, if I am going to pay my hard earned cash to replace a perfectly good mount, it is going to be a mount that is durable, lighter in weight, and functional like the Low Drag Mounts.