Monstrum Guardian 3-9x Rifle Scope with Illuminated MOA Reticle
- Rifle Scope
- 40 mm
- 3x
- 9x
- More reviewed than 71%
As an Amazon Associate, ProductDome may earn a commission from qualifying purchases made through links on this page.
How it ranks among the 359 rifle scopes we track
4.3★ across 166 Amazon ratings, Bayesian-smoothed toward the category average.
166 Amazon ratings, weighted on a log scale so huge counts don't drown everything.
Brand identity, imagery, description and spec coverage.
The ProductDome score is separate from the Amazon rating shown above: it combines the Bayesian-smoothed Amazon rating with evidence volume, tracked demand, and data quality across the 359 rifle scopes we track - how the scorecard works · full rifle scopes data report. Confidence: medium - useful but incomplete evidence.Last refreshed Jun 22, 2026. Data-computed, not a hands-on test. Compiled by the ProductDome Research Team.
Overview
A 3-9x magnification rifle scope with an illuminated MOA reticle, aircraft grade aluminum body and a nitrogen-purged sealed tube. Ships with Picatinny/Weaver rings and flip-up lens covers, positioned as a budget option for rifles and air guns out to moderate range.
Reviewers frame this consistently as a budget scope that performs above its price point rather than one that competes with premium optics. Clarity and reticle definition come up as the recurring limitation, with more than one owner noting the crosshairs aren't as crisp as pricier scopes, while several report solid results zeroing it on rimfire rifles and air guns.
- 3-9x adjustable magnification
- Illuminated MOA reticle, red or green
- Nitrogen-purged sealed aluminum tube
- 1/4 MOA click windage and elevation adjustments
Who it's for
Owners of rimfire rifles, air guns or moderate-caliber rifles who want an affordable illuminated scope for target shooting or short-range hunting. Not for anyone who needs the reticle clarity or glass quality found in premium optics.
What buyers say
From Amazon customer reviews.
Reviewers frame this as a strong value pick for the price, with several noting it outperforms their expectations on rimfire rifles and air guns and holds zero after sighting in. The most common complaint is reticle clarity, described as less crisply defined than pricier scopes, and one reviewer separately reported frustration trying to reach customer support on this and other Monstrum products.
Strengths and trade-offs
Drawn from this product's published specifications.
- Affordable option for rimfire rifles and air guns
- Red or green illuminated reticle
- Holds zero after sighting in per reviewers
- Includes mounting rings and flip-up lens covers
Specifications
| Brand | Monstrum |
|---|---|
| Model | SG3940-B |
| Dimensions & fit | |
| Objective Lens Diameter | 40 mm |
| Item Weight | 15 ounces |
| Construction & materials | |
| Material Type | Aluminum |
| Color | Black |
| Compatibility & installation | |
| Mounting Type | Weaver Mount |
| Compatible Devices | Rifle |
| Other details | |
| Magnification Minimum | 3x |
| Magnification Maximum | 9x |
| Sport Type | Hunting |
| Reticle Type | MOA Crosshair |
| Night vision | No |
| Product Style | Black | 3-9x40 |
| Field Of View | 38.7 Feet |
Other Monstrum rifle scopes
How it compares
This product against the closest alternatives we track in rifle scopes.
| Product | Amazon rating | Ratings | ProductDome score |
|---|---|---|---|
| Monstrum Guardian 3-9x Rifle Scope with Illuminated MOA ReticleThis product | 4.3 / 5 | 166 | 4.0 / 5 |
| UTG 3-12X44 30mm Compact ScopeUTG | 4.5 / 5 | 3,000 | 4.4 / 5 |
| Vortex Optics Diamondback Second Focal PlaneBrand | 4.7 / 5 | 1,500 | 4.3 / 5 |
| PINTY Tactical Rifle Scope Combo: Illuminated OpticsPinty | 4.4 / 5 | 1,100 | 4.3 / 5 |
| Firefield RapidStrike 1-6x24 SFP Riflescope KitFirefield | 4.5 / 5 | 900 | 4.3 / 5 |
Similar rifle scopes from other brands
Questions about the Monstrum SG3940-B
Common buyer questions answered straight from the product spec data - no fluff, no "it depends".
What rifles is the Monstrum Guardian scope best suited for?
Reviewers report good results on rimfire rifles like the 10/22 and on PCP air rifles at moderate range.
Does the Guardian scope hold zero after sighting in?
Multiple reviewers say it sighted in without issue and held zero on their rifles.
Is the reticle illumination adjustable in color?
Yes, it offers a choice between red and green illumination.