The RMR earned its name a long way from a UK range, on the sidearms of foreign military and police units where the only question asked of an optic was whether it still worked after years of being dropped, soaked and shot. That reputation is genuine, and close to useless for choosing between the four Trijicon models sold here — ruggedness is the floor across all of them, not what separates them. What separates them is narrower: how much window you get, whether the emitter is exposed or sealed, how the battery goes in, and what the optic is bolted to.
Window size is the first real fork in the road
The RMR Type 2 gives you a sight window of 0.87 × 0.63 in (22 × 16 mm). That is a small aperture on a small optic, and it is part of why the housing feels so solid. The cost is that the frame sits closer to your line of sight, so on a fast presentation the dot takes marginally longer to appear where you expect it.
The SRO attacks exactly that problem. Its window measures 0.98 × 0.89 in (25 × 22.5 mm) — barely wider than the RMR, but around 40 per cent taller, and round rather than rectangular. Height is what you notice. The dot is quicker to find when the gun arrives, and far easier to watch as it lifts and settles, which is why the SRO sits in the competition red dot sights category rather than alongside the compact models.
The RMR HD is the platform's largest redesign and does enlarge the window over the original RMR, but Trijicon's verified figures for this store do not include a window measurement for it, so no number is quoted here. Treat it as bigger than an RMR and judge it in person if window size is the deciding factor.
Open emitter or sealed: what the RCR is actually for
The RMR, SRO and RMR HD are all open-emitter designs. The LED sits in a well at the rear of the housing and throws its light forward onto the lens, and that well is open to the world. In dry conditions this never matters. In UK conditions it sometimes does: heavy rain on an exposed range, mud on a rough shoot, or the fine grit that gets everywhere at an outdoor airsoft site can sit in that well and dim or block the dot.
The RCR is Trijicon's answer. It keeps the recoil-deflecting RMR shape but seals the emitter behind a window, so the light path is closed. It is built from forged 7075-T6 aluminium with a hard-coat anodised finish, runs a 3.25 MOA adjustable dot across 10 brightness settings — the lowest three night-vision compatible, and the chosen level can be locked in — and weighs 1.69 oz in a 1.8 × 1.2 × 1.3 in body. Shoot mostly indoors and the sealing buys you very little; spend most weekends outside in British weather and it is the most relevant difference in the range. Our comparison of open reflex and enclosed designs covers the trade-off, and there are more sealed options in enclosed red dot sights.
Battery access decides more than it sounds like it should
On the original RMR the battery sits underneath. Changing it means unbolting the optic, and remounting means confirming your zero again. Trijicon rate the RM01 at up to around two years on a single CR2032, and the adjustable-LED versions such as the 6.5 MOA RM07 at up to around four years at setting 4, so it is not a frequent chore — but it is unavoidable, and awkward if the optic is zeroed on a certificate-held rifle you cannot casually re-zero at short notice.
The SRO, RCR and RMR HD all load the CR2032 from the top, with the sight still mounted and the zero untouched. Runtimes differ: 3+ years at setting 4 for the SRO, up to around three years for the RMR HD, and up to around six years at setting 5 for the RCR. The RCR figure is the outlier in the range by a wide margin.
The verified numbers side by side
| Model | Window | Battery access | Emitter | Water rating | Total travel |
|---|---|---|---|---|---|
| RMR Type 2 | 0.87 × 0.63 in (22 × 16 mm) | Bottom-load | Open | Submersible to 20 m (66 ft) | 150 MOA |
| SRO | 0.98 × 0.89 in (25 × 22.5 mm) | Top-load | Open | Submersible to 3 m (10 ft) | 150 MOA |
| RCR | Not published in store data | Top-load | Sealed | Not published in store data | 150 MOA |
| RMR HD | Not published in store data | Top-load | Open | Submersible to 20 m (66 ft) | Not published in store data |
Two things stand out. Every model adjusts in true 1 MOA clicks, and every one with a published figure offers 150 MOA of total travel in both axes — generous enough that these optics tolerate being moved between a pistol, a rail mount and an ACOG bracket without running out of adjustment. The other is the water rating gap: 3 m (10 ft) for the SRO against 20 m (66 ft) for the RMR and RMR HD. That is a competition optic being honest about its priorities, not a defect.
One footprint, four destinations
Everything above shares the Trijicon RMR footprint — the RCR via a patented mounting system built around the same pattern. That is the practical reason the range is worth committing to: one mount carries any of them. If the footprint idea is new, our footprints explainer covers why the patterns are not interchangeable.
Where the optic ends up determines the hardware, and this is where most orders go wrong:
- An optics-ready pistol slide. The screws in the optic's box are the long rifle-mounting ones. A milled slide needs the short screws and a sealing plate, which is what the AC32064 mounting kit supplies — cut for Glock MOS, Springfield OSP and Prodigy, Walther PDP and H&K VP9.
- A Picatinny rail, low. The RM33 (AC32004) is the low aluminium mount, sitting the dot close to the rail. This is the sensible default on a rifle with no backup irons to line up with.
- A Picatinny rail, at iron-sight height. The RM34 (AC32005) raises the optic so it can co-witness. If you are unsure whether you want that, read how to co-witness with iron sights before choosing a height you cannot change.
- On top of an ACOG. Both the RM35 (AC32007) and the RM66 (AC32029) bolt to the mounting bosses on a Trijicon ACOG body, putting an unmagnified dot above the magnified sight. Both take RMR- or SRO-footprint optics; check which bracket your ACOG model's bosses accept before ordering.
One honest gap: the ACOG itself is not stocked here despite the ACOG brackets being carried, so it would need sourcing elsewhere. The mount range and the wider Trijicon range show what is actually held.
Dot size, once you have picked a body
Dot size is a separate decision, and the two ranges do not overlap neatly: the RMR Type 2 comes in 1.0, 3.25 and 6.5 MOA, the SRO in 1.0, 2.5 and 5.0 MOA. Bigger dots are faster to find and cover more target; finer dots aim precisely and are easier to lose under recoil.
For a rifle used on paper or for quarry at distance, the 1.0 MOA RM09 or the finest SRO covers the least target. For practical shooting where the clock matters, the 5.0 MOA SRO is the quickest to acquire. The 3.25 MOA RM06 is the middle ground, and is also made as a green dot for eyes that separate green from a cluttered background faster than red. The RMR HD sidesteps the question by combining a 55 MOA segmented circle with a fine centre dot — 1.0 MOA on one version, 3.25 MOA on the other — and toggling to dot-only when the circle is in the way. If MOA is not yet a unit you think in, what MOA means converts it to coverage on target.
Where these fit in UK shooting
Three settings account for most Trijicon sales in Britain, and each pushes the choice differently.
Airsoft. The RMR footprint is the most widely cloned pattern in airsoft, so a genuine Trijicon will physically fit a great deal of airsoft kit. Airsoft guns sit outside the firearms regime: the Firearms Act 1968 section 57A, inserted by the Policing and Crime Act 2017, defines an airsoft gun as a barrelled weapon designed to discharge only a small plastic missile — spherical, made wholly or partly from plastics, not exceeding 8 mm in diameter — and not capable of exceeding the permitted kinetic energy at the muzzle. Those permitted levels are 1.3 joules for a weapon capable of discharging two or more missiles successively without repeated pressure on the trigger, and 2.5 joules in any other case. Airsoft is where optics get knocked and rained on hardest, so the sealed RCR or the RMR's deeper 20 m rating make more sense here than the SRO.
Air rifles and air pistols. The Guide on firearms licensing law sets the exempt thresholds at 12 ft lb for an air rifle and 6 ft lb for an air pistol (s.2.46). Scotland is separate: section 2 of the Air Weapons and Licensing (Scotland) Act 2015 makes it an offence to use, possess, purchase or acquire an air weapon in Scotland without an air weapon certificate issued by Police Scotland (s.2.52). Northern Ireland has its own firearms legislation entirely (s.4.5). Confirm your own position with your police firearms licensing department before buying anything that will be fitted to an air weapon.
Certificate-held rifles and long-barrelled pistols. Long-barrelled pistols and revolvers may be held on a firearm certificate where their dimensions exceed those stipulated in section 5(1)(aba) of the Firearms Act 1968. On a certificate-held gun the top-loading battery on the SRO, RCR and RMR HD stops being a convenience and starts being the feature that means an optic change does not cost you a range session re-zeroing — see how to zero a red dot sight for what that process actually involves. The rest of the pistol dot sight range sits alongside these if the Trijicon price bracket is more than the job needs.
Narrowing it down
If the gun lives outdoors and gets wet, the RCR's sealed emitter is the difference that matters and its six-year runtime is a bonus. If you shoot against a clock, the SRO's taller round window is what you are paying for and the shallower 3 m rating is the price. If you want the smallest, hardest optic and will unbolt it every couple of years, the RMR Type 2 remains the compact benchmark. And a circle-dot reticle with a top-loading battery on this footprint is the RMR HD alone.