Trijicon RMR vs Aimpoint Acro P-2: Open vs Enclosed Duty Dot

A drop of rain on the wrong spot

An open-emitter pistol dot has a tiny LED sitting at the back of the sight, firing forward onto a coated window. Between that LED and the window there is nothing but air. Most of the time that is fine. But a drop of water, a smear of mud or a bit of pocket lint landing on the emitter can block the dot. An enclosed emitter puts a second pane of glass behind the LED and seals the whole path.

The Trijicon RMR is the open-emitter dot many other pistol optics are measured against, and its footprint became a de facto standard. The Aimpoint Acro, which Aimpoint launched in 2018 and updated as the second generation in 2021, was built from the start as a fully enclosed pistol sight. Comparing them is really comparing two philosophies.

The site already explains the general trend in its enclosed-emitter guide. This piece is narrower: these two specific dots, for a duty or carry pistol.

The numbers from each maker

Specs below come from Trijicon's RMR specification sheet and Aimpoint's Acro P-2 product page. The RMR figures are for the Type 2 adjustable LED model.

Two things jump out. The RMR is close to half the weight and noticeably lower. The Acro is sealed, deeper-rated for water and has a longer listed battery life.

Open emitter: what the RMR gets right

Size and weight. At a listed 33.2 g, the RMR adds very little mass to a slide. A lighter dot puts less inertia on the slide and the mount screws during recoil, and a lower sight puts the dot closer to the bore. That lower height can matter when you want to cowitness with standard-height or slightly taller iron sights, which helps if the dot ever goes dark.

Auto brightness. Trijicon lists an automatic mode on the adjustable LED model, alongside eight manual settings. For carry, where you might walk from bright sunlight into a dim room, auto brightness is a useful feature. The site's guide to pistol dot reticle size covers how dot size and brightness interact.

The footprint ecosystem. The RMR footprint has been copied widely, and many slides, plates and mounts are cut for it. The site's footprint explainer shows how that family tree works. If you own several pistols, an RMR-pattern dot is often the easiest to move between them, though always check that the specific mount or slide cut matches.

The cost of the open design. The emitter is exposed. Rain, sweat, lint and mud can block it. That is manageable with a habit of checking the window and emitter, but it is a real difference from the Acro.

Enclosed: what the Acro P-2 gets right

Nothing in the beam path. The Acro's sealed housing means debris cannot land on the emitter. Aimpoint calls the Acro the first fully enclosed pistol optic. For a duty pistol that lives in a holster outdoors, through every kind of weather, that is the strongest argument for it.

Battery life. Aimpoint lists 50,000 hours at daylight setting 6. The RMR's 4+ years at setting 4 of 8 is also excellent, but the two figures are measured at different settings, so the fairest reading is that both run for years and the Acro has the longer published figure.

Deeper water rating. Aimpoint lists 35 m submersion, compared with the RMR's listed 20 m. Neither depth is relevant to most people, but a deeper rating suggests a robust seal.

The cost of the enclosed design. The Acro is taller (31 mm against the RMR's 25 mm) and heavier (61 g against 33.2 g). A taller sight usually needs taller iron sights to cowitness. It also adds a little more bulk on a carry pistol.

Mounting on a Glock MOS and other optics-ready pistols

Neither dot drops directly onto most optics-ready slides without the right interface. Glock's MOS system, for example, relies on adapter plates, and you will need one that matches the dot you choose. Some slides are milled directly for the RMR footprint, and some makers now cut slides for the Acro interface.

The rules are the same whichever you choose:

• Use the plate or slide cut specifically made for your dot's footprint.
• Use the screws the plate or dot maker supplies, at the correct length. A screw that is too long can bottom out against something in the slide.
• Torque the screws to the maker's spec. Do not guess. Trijicon, Aimpoint and plate makers publish their own values, and the site's mounting torque guide explains why they differ.

Cowitness and iron sights

Backup iron sights matter more on a pistol dot than on a rifle dot, because a pistol dot is your only sighting system once it goes dark. The usual approach is "suppressor-height" iron sights, taller than standard, that show through the bottom of the dot's window.

Height is where these two designs part ways. Trijicon lists the RMR at 25 mm tall, and Aimpoint lists the Acro P-2 at 31 mm. Aimpoint also gives an optical axis height of 14 mm above the mounting interface. Plate thickness and slide cut depth change the final number, so the only reliable way to know whether a given set of irons will cowitness is to check the iron sight maker's recommendations for your exact dot and plate.

In general, expect to need taller irons for the Acro. Some shooters skip irons entirely and rely on the dot's battery life and their maintenance habits. That is a personal choice, but it is worth making deliberately rather than by accident.

Living with each one

Battery changes. Both use a CR2032. Check the manual for how the battery is accessed on your model, since that affects whether you need to remove the sight from the slide. A sight that must come off for a battery change also needs its zero confirmed afterward. Many owners change batteries on a fixed schedule rather than waiting for the dot to fade.

Cleaning. The open RMR needs its emitter and window kept clear. A quick check before carrying is a good habit. The Acro's sealed housing means you only clean the outside surfaces, but those still collect dust and fingerprints.

Brightness. The RMR's auto mode can handle changing light by itself. Aimpoint lists the Acro P-2 with six daylight and four night vision settings and no automatic mode on its spec page, so plan to choose a brightness and adjust it when conditions change.

Which one for which job

Duty pistol, outdoors, all weather. The Acro P-2's sealed housing is the more forgiving choice. Debris is a real threat in a duty holster, and the extra weight and height are reasonable trade-offs.

Concealed carry, mostly indoors and urban. This one is closer. The RMR is lower and lighter, which helps concealment and cowitness. The Acro rules out lint on the emitter, which is a concern for inside-the-waistband carry under clothing. Many carriers pick the RMR for size and check it daily. Others prefer not to think about it and choose the Acro.

Range and competition. The RMR's light weight and auto mode are attractive. The Acro's enclosed design matters less on a clean range.

Multiple pistols. If several of your guns are already cut for the RMR footprint, the RMR or an RMR-pattern dot will be simpler.

Where to look

Ammunition Depot lists the Trijicon RMR Type 2 RM06 3.25 MOA adjustable LED and the smaller Trijicon RMRcc for subcompact slides; confirm which footprint your slide is cut for before ordering either. For the Aimpoint, Optics Planet carries the Acro line, including the P-2 in several dot sizes.

If you want to compare more open and enclosed options, the Ammunition Depot red dot category lists both styles from many brands.

Verdict

Both dots are made by companies with long records in duty optics, and either is a serious choice. The decision comes down to whether you value the RMR's lower, lighter profile and footprint ecosystem more than the Acro's sealed emitter and longer listed battery life.

Editorial note: This is an independent editorial overview built from manufacturer specifications, retailer listings and published sources. We have not performed hands-on testing of the products discussed, and nothing here is a performance guarantee. Verify specifications, compatibility and the law where you live.

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