5 Best Red Dot Sights for the Glock 21 Handgun

Chris G.

As a firearms enthusiast and competitive shooter, I recognize the significance of having a top-notch red dot sight for my Glock 21 handgun. The impact of these sights on accuracy and the speed of target acquisition is undeniable, significantly elevating my overall shooting experience.

I’ve tested, read reviews, and assessed numerous top-rated sights, exploring offerings from renowned brands such as Trijicon, Leupold, Burris, Vortex, and Holosun. In this review, I’ll help you in finding the ideal match for your Glock 21.

I’ll uncover the distinctive features and advantages of each red dot sight, delivering valuable insights to empower you in making a well-informed decision in choosing a red dot tailored to your Glock 21 preferences.

Top 5 Red Dot Sights for the Glock 21 Handgun

Here are the top five red dot sights for the Glock 21 handgun that I’ve carefully selected.

These options include the:

• Trijicon RMR Type 2 and SRO

• Leupold DeltaPoint Pro

• Burris FastFire 3


I’ll go through each of these red dot sights in detail.

1. Trijicon RMR Type 2 RM06-C-700677: Best Choice

When it comes to finding the best red dot sight for the Glock 21 handgun, I strongly recommend the Trijicon RMR Type 2 as an excellent choice.

The patented housing which is made of military-grade aluminum effectively absorbs impacts and disperses stresses away from the lens.

This red dot sight offers a 3.25 MOA adjustable RMR LED. The sides of the sights have easy-to-use buttons that allow you to adjust the illumination, switch between manual and automatic modes, and power down the RMR for storage. The LED automatically shuts off when not in use and turns on when it detects movement. This allows me to save the battery as it only powers up when I start shooting. In addition, the RMR LED is compatible with night vision devices.

Another thing I like about the RMR 2 is the lock-out buttons. This makes sure that I do not inadvertently change button settings and cause the loss of an aiming solution. This feature can only be used in automatic mode only. 

With its automatic brightness mode and eight adjustable brightness settings, the Trijicon RMR Type 2 ensures clear visibility in various lighting conditions.

While it may have a higher price point, its performance, quality, and durability make it worth the investment. I can’t actually find any reason to skip the Trijicon RMR Type 2.

Technical Specifications

Length x Width x Height: 1.8 in x 1.1 in x 1 in
Weight: 1.2 oz. 
Magnification: 1x
Reticle Pattern: 3.25 MOA Dot
Adjustment: 1 MOA Per Click
Day Reticle Color: Red
Night Reticle Color: Red
Illumination Source: RMR LED
Power Source: 3V Lithium Battery
Battery Life: Over 4 years of continuous use
Mount: RM36 ACOG Mount
Housing Material: Forged Aluminum
Finish: Matte Black

Special Features

  • Design and Construction
    • Rugged and durable forged aluminum housing.
    • Waterproof up to 20 meters (66 feet) to ensure reliability in various environments.
  • Reticle Options
    • Available with a variety of reticle options, including 3.25 MOA and 6.5 MOA dot sizes.
    • Adjustable LED reticle brightness for different lighting conditions.
  • Battery Life
    • Long battery life, with the ability to run continuously for several years on a single CR2032 battery.
    • Battery conservation mode helps extend battery life.
  • Adjustment Controls
    • Easy-to-use windage and elevation adjustments for precision sighting.
    • Audible clicks and tactile feedback for more straightforward adjustments.
  • Trijicon RMR Type 2 Enhanced Electronics
    • Redesigned and upgraded electronics for increased durability and performance.
    • Resistant to harsh recoil and impact forces.
  • Multiple Mounting Options
    • Versatile mounting options, including a variety of compatible mounts for different firearms.
    • Compatible with various adapter plates for easy integration with different pistol models.
  • Auto Adjust Mode
    • Automatic brightness adjustment based on ambient lighting conditions.
    • Manual brightness override is available for user customization.
  • Parallax-Free Performance
    • Parallax-free design for rapid target acquisition and improved accuracy.
    • Minimal point-of-impact shift during recoil.
  • Button Lockout Mode
    • Option to lock the adjustment buttons to prevent unintentional changes to the sight settings.
  • Co-Witness Capability
    • Compatible with suppressor height sights for co-witnessing with backup iron sights.


  • Cost: Trijicon optics, including the RMR Type 2, are not for budget-conscious buyers. Still, I strongly recommend you get the RMR 2 if you can afford it. It’s the best value for your money.

2. Trijicon SRO: Best for Competitive Shooting

If you’re an avid competitive shooter like me, you should seriously consider the Trijicon SRO (Specialized Reflex Optic). This line from Trijicon is another great option for competitive shooting, alongside the top choice, the Trijicon RMR Type 2. 

It offers a large field of view and a clear, crisp 5.0 MOA red dot, which is technically superior to the RMR. In fact, I find the SRO’s reticle clearer and more distinct even when the sun is at its highest. The SRO has both manual and automatic LED brightness, allowing it to adjust with the ambient lighting automatically. Target acquisition and engagement are fast and easy.

This red dot sight is made of durable 7075 T-6 aircraft-grade aluminum designed to withstand the rigors of slide-ride pistols like the Glock 21. I find the housing incredibly solid; I’m confident my SRO can survive a long pistol-mounted drop during intense shooting.

The SRO’s has a footprint that matches the RMR, making installation effortless, especially on your Glock 21. While some users have mentioned minor issues like the absence of included screws and occasional sight distortion in bright sunlight, my overall experience on the SRO’s performance is positive.

Technical Specifications

Length x Width x Height: 2.2 in x 1.3 in x 1.4 in
Weight: 1.6 oz. 
Magnification: 1x
Reticle Pattern: 5.0 MOA Dot
Adjustment: 1 MOA Per Click
Adjustment Range: 150 MOA Total Travel
Illumination Source: LED
Illumination Settings: Automatic and 8 Adjustable Settings (2 NV, 6 Visible)
Power Source: 1 CR2032 Lithium Battery
Battery Life: Over 3 years of continuous use
Mount: Not Included
Housing Material: 7075-T6 forged aluminum
Finish: Matte Black
Submersion Depth: 10 ft. 

Special Features

  • Large Field of View
    • The SRO’s large window size allows for faster target acquisition and improved situational awareness.
  • Top-Loading Battery Design:
    • The SRO incorporates a top-loading battery compartment, allowing users to replace the battery without removing the sight from the firearm. 
  • Automatic and Manual Brightness Modes
    • The SRO offers multiple brightness settings, including an automatic mode that adjusts the dot brightness based on ambient lighting conditions. Users can also manually adjust the brightness settings to suit their preferences and shooting conditions.
  • Rugged Construction
    • Built with a forged aluminum housing, the SRO is designed to be durable and withstand recoil forces and harsh environmental conditions. It is constructed to be rugged and reliable in various shooting scenarios.
  • Parallax-Free Design
    • The reticle remains on target regardless of the shooter’s eye position. This feature enhances accuracy and target engagement.
  • Easy-to-Use Windage and Elevation Adjustments
    • The SRO is equipped with user-friendly controls for windage and elevation adjustments. 
  • Compatibility with Various Mounting Systems
    • The SRO is designed to be compatible with various mounting systems, making it adaptable to different firearms.
  • Enhanced Electronics
    • The electronics within the SRO are designed to be advanced and durable, providing reliable performance even in demanding conditions. This includes resistance to recoil forces and impact.


  1. Weight and Size: Some users may find the SRO to be relatively larger and heavier compared to other compact reflex sights. This can impact the overall balance of the firearm.
  2. Price: The SRO is more expensive than other red dot sights in the market. 
  3. Limited Reticle Options: The SRO has a fixed 5.0 MOA dot size. If you prefer a different or adjustable reticle size, they may need to explore other options.

3. Burris FastFire 3: Best Value for Money

Not all shooters are rich. For those on a tight budget, I can recommend the Burris FastFire 3. This top-quality sight offers excellent value for your money without compromising performance or durability.

With its unmatched clarity and brightness, the FastFire 3 ensures quick target acquisition with its 3-MOA Dot Reticle. Based on my testing, it’s big enough to see during daylight but won’t obstruct smaller targets. Similar to the Trijicons, you can set the brightness manually or automatically. In the latter mode, a light sensor detects the ambient light and adjusts the brightness level accordingly. The lens is coated to maximize light transmission. 

I appreciate its durability even though I felt it’s a tad on the low end. However, it does withstand recoil and maintain the zero. Plus, the tool-less windage and elevation adjustments allow for precise shooting. The red dot sight is made of aluminum and can be submerged.

Technical Specifications

Power Source: 1 x CR1632
Magnification: 1x
Sight Window Dimensions: 0.8 x 0.6 inches
Impact Point Correction: 1 MOA
Windage Adjustment: 86 MOA
Elevation Adjustment: 115 MOA
Operating Temperature: -10 to 130°F / -23 to 55°C
Water Resistance: Waterproof
Parallax-Free: 10 to 150 yards
Dimensions: 1.9 x 1.0 x 1.0 inches
Weight: 0.9 oz.
Housing: Aluminum
Finish: Matte-black corrosion and scratch-resistant anodized finish

Special Features

  • Compact and Lightweight Design
    • The FastFire 3 has a compact and lightweight design.
  • 3 MOA Dot Reticle
    • The sight features a 3 MOA red dot reticle, providing a good balance between precision and fast target acquisition.
  • Top-Mounted Battery
    • The FastFire 3 incorporates a top-mounted battery design, allowing users to replace the battery without removing the sight from the firearm. 
  • Automatic Brightness Sensor
    • The FastFire 3 includes an automatic brightness sensor that adjusts the dot intensity based on ambient lighting conditions. 
  • Windage and Elevation Adjustments
    • The FastFire 3 features windage and elevation adjustments to allow users to zero the sight for precise shot placement. 
  • Parallax-Free Design
    • The FastFire 3 is designed to be parallax-free at 10 to 150 yards, ensuring that the reticle remains on target regardless of the shooter’s eye position.
  • Low Profile and Co-Witness Mounts
    • The FastFire 3 is compatible with low-profile mounts for a streamlined appearance and co-witnessing with iron sights. This compatibility allows users to maintain situational awareness with backup sights.
  • Waterproof Construction
    • The FastFire 3 is designed to be waterproof, with seals to protect against moisture and environmental elements


  1. Durability Under Heavy Recoil: Although this hasn’t happened to me, some users have reported concerns about its performance under heavy recoil, especially on high-caliber firearms. It’s important to consider the specific application and firearm compatibility.
  2. No Mount: One of the downsides of the FastFire 3 is that it comes without a mount. You have to purchase the right mount separately.
  3. Controls and Adjustment Knobs: The controls and adjustment knobs make precise adjustments quite challenging, especially for users with big hands like mine.
  4. Lens Clarity: There’s a certain degree of distortion, particularly at certain brightness settings.

4. HOLOSUN HS507C X2: Budget Alternative

Despite being budget-friendly, the open reflex optical sight HOLOSUN HS507C X2 offers a wide range of features that make it a great alternative to more expensive red dot sights for the Glock 21 handgun.

The HS507C X2 has a Lock Mode that, when activated, locks the buttons preventing inadvertent setting changes. This is especially useful during fast and high-movement situations. 

It also features Solar Failsafe Technology, one of the reasons why I have my Holosun with me. If my battery fails, I’ll still have power as long as there’s natural or artificial light available. My HS507C X2 has a supercapacitor that allows me to theoretically run the red dot indefinitely by maintaining a charge. The reticle intensity adjusts automatically although there’s also a manual mode. 

Another feature I like is the side-mounted battery tray for easy battery replacement. The battery life is exceptional, lasting around 50,000 hours.

For a reasonable price, the Holosun HS507C X2 is an amazing bargain. 

 Technical Specifications

Reticle: 2 MOA Dot and 32 MOA Circle
Light Wavelength: 540nm
Reticle Color: Red or Green, depending on the variant
Parallax Free: Yes
Unlimited Eye Relief: Yes
Magnification: 1x
Multi-Coatings: Yes
Power Source: Solar and Battery
Battery Type: CR1632
Battery Life: 50000 hours
Brightness Setting: 10 Daylight and 2 Night Vision
Window Size: 0.63×0.91 inches
Dimension: 1.78 x 1.15 x 1.15 inches
Weight: 1.5 oz.
Housing Material: 7075 T6 Aluminum
Surface Finish: Anodized
Adjustment per Click: 1 MOA
Wind and Elevation Travel Range: ±50 MOA
Storage Temperature: -40℃~70℃
Working Temperature: -30℃~60℃
Submersion: IP67
Vibration: 5000G

 Special Features

  • Multiple Reticle Options
    • The HS507C X2 offers a 2 MOA dot, a 32 MOA circle, and a circle-dot combination. This provides users with the flexibility to choose the reticle that best suits their preferences and shooting style.
  • Solar Failsafe
    • The Solar Failsafe technology harnesses solar power to operate the sight when there is sufficient light. In the absence of adequate light, the sight switches to battery power, ensuring continuous operation.
  • Shake Awake Technology
    • The Shake Awake feature automatically activates the sight when motion is detected and puts it to sleep when there is no movement. This helps conserve battery life and ensures that the sight is ready for use when needed.
  • Multiple Reticle System (MRS)
    • The MRS allows users to switch between reticle options easily, providing versatility for different shooting scenarios.
  • Multi-Coated Lens
    • The lens is multi-coated to reduce glare and improve light transmission, resulting in a clear and crisp sight picture.
  • Side-Mounted Battery
    • The HS507C X2 features a side-mounted battery compartment, making it convenient for users to replace the battery without removing the sight from the firearm.
  • IP67 Certified
    • The HS507C X2 is IP67 certified for water resistance, providing protection against water immersion up to 1 meter for a limited duration. This makes the sight suitable for use in various weather conditions.
  • Parallax-Free Design
    • The HS507C X2 is parallax-free. The reticle remains on target regardless of the shooter’s eye position.
  • Motion Sensor Technology
    • The sight includes a motion sensor that activates the reticle when motion is detected, contributing to quick target acquisition.
  • Toolless Battery Compartment
    • The battery compartment is designed to be toolless, allowing for quick and easy battery changes in the field.
  • Locking Screw for Windage and Elevation Adjustments
    • The windage and elevation adjustments come with a locking screw, providing additional security once the sight is zeroed.


  1. Lens Clarity Issues: Some users have reported concerns with lens clarity and distortion, particularly at certain brightness settings.
  2. Compatibility with Some Holsters: Due to its design and size, the HS507C X2 may not fit some holsters designed for specific firearms with other optics. Users should check holster compatibility before purchasing.

5. Leupold DeltaPoint Pro: Strong Build

The Leupold DeltaPoint Pro is the perfect shooting buddy if you’re going out in the wilderness or if you’re expecting to be battered by Mother Nature. The sight is known for its durable construction and high-quality optics. The DeltaPoint Pro is built to withstand the elements, being 100% waterproof, fogproof, and shockproof. 

This sight offers excellent light transmission and glare reduction, thanks to its professional-grade optical system. It also includes an illuminated reticle for low-light conditions and Motion Sensor Technology (MST) to extend battery life.

While there have been some reported issues with mounting screws, its compatibility and easy installation on various firearms have made it a popular choice for Glock 21 owners.

Technical Specifications

Battery Type: CR2032
Daylight Bright Illumination: Yes
Elevation Adjustment Type: Coin Click
Magnification Type: Fixed
Magnification Min: 1
Reticle Focal Plane: Second Focal Plane
Reticle: 2.5 MOA Dot
Reticle Type: Illuminated
Switch Type: Push Button
Windage Adjustment Type: Coin Click
Weight: 2 oz.
Elevation Adjustment Value per Click: 1 MOA
Elevation Adjustment Range: 60 MOA
Elevation Adjustment Range: 17 MIL
Elevation Adjustment Range: 175 cm at 100 meters
Elevation Adjustment Per Revolution: 40 MOA
Elevation Dial Travel Limit: Total Scope Travel
Windage Adjustment Value per Click : 1MOA
Windage Adjustment Range: 60 MOA
Windage Adjustment Range: 17 MIL
Windage Adjustment Range: 175 cm at 100 meters
Windage Adjustment Per Revolution: 15 MOA
Eye Relief Low Mag: Unlimited
Battery Life, Low Intensity: 1600 hours
Battery Life, Medium Intensity: 1000 hours
Battery Life, High Intensity: 300 hours
Number of Illum Settings: 8


  • Motion Sensor Technology
    • The DeltaPoint Pro features a motion sensor that automatically activates the illumination when it detects motion. This helps extend battery life by putting the sight to sleep when not in use.
  • DiamondCoat Lens Coating
    • Leupold’s DiamondCoat lens coating provides abrasion resistance and enhanced light transmission, contributing to a clear and bright sight picture.
  • Toolless Windage and Elevation Adjustments
    • The sight is designed with toolless windage and elevation adjustments, allowing users to make quick and easy adjustments in the field without the need for additional tools.
  • Aspheric Lens Technology
    • The aspheric lens design helps eliminate distortion, providing a clear and distortion-free sight picture.
  • Extended Battery Life
    • The DeltaPoint Pro is known for its extended battery life, providing users with reliable performance over an extended period. The motion sensor technology further contributes to power efficiency.
  • Dual-Illumination System
    • The sight features a dual-illumination system with a versatile red dot reticle. It includes both manual brightness adjustment settings and an automatic mode that adjusts the brightness based on ambient lighting conditions.
  • Toolless Battery Replacement
    • The battery compartment is designed to be toolless, simplifying the process of replacing the battery in the field.
  • Integrated Rear Iron Sight
    • The DeltaPoint Pro has an integrated rear iron sight that serves as a backup sight for co-witnessing with the red dot reticle. This feature enhances the user’s ability to engage targets effectively.
  • Rugged Construction
    • The sight is built with a rugged aluminum housing, making it durable and capable of withstanding recoil forces and harsh environmental conditions.
  • Waterproof and Fogproof
    • The DeltaPoint Pro is waterproof, providing protection against moisture and environmental elements. It is also fogproof, ensuring clarity in various weather conditions.
  • Wide Field of View
    • The sight is designed to provide a wide field of view, enhancing situational awareness and target acquisition speed.
  • Easy Mounting
    • The DeltaPoint Pro is compatible with a variety of mounting systems, making it easy to integrate with different firearms.
  • Low Profile Design
    • The sight has a low profile, contributing to a sleek and unobtrusive appearance on the firearm.
  • Scratch-Resistant Lenses
    • The lenses are built to be scratch-resistant, maintaining optical clarity and durability over time.


  1. Price: The DeltaPoint Pro is positioned in the higher price range compared to some other red dot sights. Cost can be a factor for budget-conscious users.
  2. Weight: Some users may find the DeltaPoint Pro relatively heavier compared to other compact red dot sights. This weight may impact the overall balance. of the firearm.
  3. Holster Compatibility: Due to its design and size, the DeltaPoint Pro may not be compatible with all holsters designed for specific firearms with other optics. Users should verify holster compatibility before purchasing.

Installation and Usage Tips for Red Dot Sights on the Glock 21

Now that we’ve discussed the top red dot sights for the Glock 21, let’s move on to some practical tips. I’ll provide you with step-by-step instructions on installing your red dot sight correctly on your Glock 21. I’ll also show you the proper way of zeroing the sight for optimal performance and offer maintenance tips to ensure it stays in excellent condition.

Adding a Red Dot Sight to Your Glock 21

Installing a red dot sight on a Glock 21 is easy and involves a few simple steps. I usually do these general steps. Keep in mind that it’s essential to refer to the manufacturer’s instructions for your specific red dot sight and mounting plate because installation procedures may vary.

Tools and Materials

  1. Glock 21 handgun
  2. Red dot sight
  3. Mounting plate (if required)
  4. Appropriate mounting screws
  5. Screwdriver or Allen wrench (size may vary)
  6. Torque wrench (optional, but recommended)


  1. Ensure Safety
    • Before starting, ensure that the Glock 21 is unloaded and the chamber is clear. Follow basic firearm safety practices.
  2. Select the Mounting Plate
    • If your red dot sight requires a mounting plate, select the appropriate one for your Glock model. Some red dot sights come with specific plates, while others may require a separate purchase.
  3. Remove the Slide
    • Field-strip your Glock 21 by removing the slide from the frame. This typically involves pulling back slightly on the slide, pulling down the slide lock tabs on both sides, and then releasing the slide forward.
  4. Mounting Plate Installation
    • If using a mounting plate, install it on the slide according to the manufacturer’s instructions. This often involves securing the plate with screws provided by the manufacturer.
  5. Attach the Red Dot Sight
    • Place the red dot sight on the mounting plate. Align the screw holes on the sight with those on the mounting plate.
  6. Secure the Red Dot Sight
    • Insert the appropriate screws through the sight and into the mounting plate. Tighten the screws securely, but be cautious not to over-torque them, as this can damage the sight or the mounting plate.
  7. Check Alignment
    • Ensure that the red dot sight is properly aligned. Check for any movement or play in the mounting. Some red dot sights have specific alignment procedures outlined in their user manuals.
  8. Tighten to Manufacturer’s Specifications
    • If you’re using a torque wrench, tighten the mounting screws to the torque specifications provided by the red dot sight manufacturer. This ensures that the sight is securely attached without over-torquing.
  9. Reassemble the Firearm
    • Reassemble the Glock 21 by placing the slide back onto the frame. Ensure that the slide is fully forward, and perform a function check to ensure proper reassembly.

Always refer to the specific instructions provided by the red dot sight and mounting plate manufacturers. If you’re unsure about any step, seek assistance from a professional gunsmith or contact the manufacturers for guidance. 

How to Zero a Red Dot on the Glock 21 for Optimal Performance

Once you’ve successfully installed a red dot sight on your Glock 21, it’s important to zero it in for optimal performance. This is how I do it. 


  1. Prepare the Firearm
    • Ensure the Glock 21 is unloaded, the chamber is clear, and the firearm is safe.
  2. Set Up a Stable Shooting Platform
    • If possible, use a shooting rest or sandbags to stabilize the handgun. This helps reduce shooter-induced errors during the zeroing process.
  3. Choose a Target Distance
    • Select a target distance that is appropriate for your shooting needs. A common starting point is 25 yards, but you can choose a distance that aligns with your typical usage scenario.
  4. Adjust Brightness Settings
    • Set the brightness level of your red dot sight to a level that is comfortable for your shooting conditions. Ensure that the dot is visible without being too bright or too dim.
  5. Take a Few Shots
    • Fire a few rounds at the center of the target using a stable shooting platform. Aim at the center of the target using the red dot sight.
  6. Evaluate Shot Placement
    • Examine the impact of your shots on the target. Note the distance and direction of the shots from the desired point of impact.
  7. Make Preliminary Adjustments
    • If the shots are consistently off-center, use the windage and elevation adjustments on your red dot sight to move the point of impact towards the desired point of aim. Refer to your sight’s manual for information on adjusting these settings.
  8. Continue Firing and Adjusting
    • Fire additional rounds, making slight adjustments to the windage and elevation settings as needed. Continue this process until the shots consistently hit the target at the desired point of aim.
  9. Confirm Zero
    • Once you’ve made adjustments, fire a few more rounds to confirm that your red dot sight is zeroed. Check for consistency in shot placement.
  10. Record Zero Settings:
    • Once satisfied with your zero, record the windage and elevation settings. This information can be useful for future reference or if you need to re-zero the sight.
  11. Test at Different Distances:
    • If possible, test the zero at different distances to ensure that it remains consistent across various engagement ranges.

Zeroing is a dynamic process, and factors like ammunition type, shooting conditions, and individual shooting technique can affect your zero. It’s advisable to re-check and adjust your zero periodically, especially if you change ammunition or encounter significant environmental changes. 

Important Maintenance Tips for Keeping Your Red Dot Sight in Top Condition

I’m a stickler for excellence. To do so, I keep my firearms and accessories in top shape all the time. Let me share some important maintenance tips in keeping red dot sights in top condition:

  1. Regular Cleaning
    • Clean the lenses regularly using a lens cleaning solution or a lens cleaning kit. Use a microfiber cloth to gently wipe away dirt, smudges, or debris. Avoid using abrasive materials that could scratch the lenses.
  2. Protective Covers
    • When not in use, use protective covers or lens caps to shield the lenses from dust, moisture, and scratches. This helps preserve the clarity of the lenses over time.
  3. Battery Maintenance
    • Check the battery regularly to ensure it has sufficient power. Replace the battery at regular intervals, even if it seems to be functioning, to avoid unexpected failures. Some sights have motion-activated features that extend battery life.
  4. Top-Up Battery Charge
    • For sights with solar panels, ensure that the solar cell is exposed to light regularly to maintain a charge. This can be particularly important for sights with solar failsafe features.
  5. Secure Mounting
    • Periodically check the mounting screws to ensure they are secure. Vibrations from recoil can cause screws to loosen over time. Use a torque wrench to tighten screws to the manufacturer’s specifications to prevent over-tightening.
  6. Weatherproofing
    • Ensure that your red dot sight is suitable for the conditions you’ll be using it in. If the sight is not fully waterproof, avoid exposing it to heavy rain or submersion. Consider adding additional weatherproofing or protective coatings if needed.
  7. Check for Damage
    • Regularly inspect the sight for any signs of physical damage, such as cracks, dents, or scratches. Address any issues promptly to prevent further damage.
  8. Rezero After Removal
    • If you remove the red dot sight from your firearm, be prepared to rezero it when reinstalled. Changes in mounting or handling can impact zero settings.
  9. Store in a Case
    • When not in use, store your firearm with the red dot sight in a padded case to protect it from dust, humidity, and potential impacts.
  10. Avoid Harsh Cleaners
    • Use cleaning solutions specifically designed for optics. Avoid harsh solvents or chemicals that could damage lens coatings or the sight housing.
  11. Follow Manufacturer’s Guidelines
    • Adhere to the manufacturer’s maintenance guidelines provided in the user manual. Different red dot sights may have specific recommendations for care and maintenance.
  12. Zero Verification
    • Periodically verify that your red dot sight is still zeroed. Changes in environmental conditions, handling, or recoil may impact the zero settings.

Troubleshooting Common Issues with Red Dot Sights

Troubleshooting common issues with red dot sights involves identifying and addressing problems that may affect their performance. Here are some common issues and steps to troubleshoot them:

  1. No Reticle or Dot is Not Illuminated
    • Check the Battery: Ensure that the battery has sufficient power. Replace the battery with a fresh one, following the manufacturer’s recommendations.
    • Check Battery Orientation: Confirm that the battery is inserted correctly, observing the correct polarity.
    • Adjust Brightness Settings: Increase the brightness setting to make the reticle more visible. In bright daylight, a higher intensity may be necessary.
  2. Dot Flickering or Inconsistency
    • Battery Issues: Check the battery for proper installation and charge. Flickering may occur if the battery is loose or losing power.
    • Contacts and Connections: Inspect the battery contacts and connections for cleanliness and proper contact. Clean if necessary.
  3. Shifted Zero or Inconsistent Accuracy
    • Check Mounting Screws: Ensure that the mounting screws are tight and secure. Vibration from recoil can cause shifts in zero.
    • Rezero the Sight: If the sight was removed and reattached, rezero it to ensure accuracy.
    • Inspect for Damage: Look for any physical damage or defects that could affect the sight’s performance.
  4. Lens Clarity Issues
    • Clean the Lens: Use a lens cleaning kit to clean the lens. Be gentle and avoid using abrasive materials.
    • Check for Scratches: Inspect the lens for scratches that may impact visibility. Replace the lens if necessary.
  5. Foggy or Moisture Inside the Lens
    • Waterproof Seal Check: Ensure that the sight’s waterproof seals are intact. If there is moisture inside, contact the manufacturer for assistance.
    • Store Properly: Avoid sudden temperature changes, and store the firearm in a dry place with a desiccant to prevent moisture buildup.
  6. Motion Activation Issues
    • Ensure Motion is Detected: Some sights have motion-activated features. Confirm that the sight is set to activate with motion and that it’s functioning correctly.
    • Check Battery and Solar Power: If applicable, ensure that the battery is charged and that the solar cell is exposed to light.
  7. Parallax Issues
    • Check Parallax Settings: If your sight has adjustable parallax, make sure it’s set correctly for the distance you’re shooting. Some red dot sights are designed to be parallax-free.
  8. Distorted Reticle Shape
    • Inspect Lens and Reticle: Check for any dirt, debris, or damage on the lens or reticle. Clean the lens, and if the distortion persists, contact the manufacturer.
  9. Crosshair or Reticle Alignment Issues
    • Recenter the Reticle: If the reticle appears off-center, check if your sight has a recentering feature. If not, you may need to send it to the manufacturer for adjustment.
  10. Dim or Faint Reticle
    • Adjust Brightness Settings: Increase the brightness setting to improve visibility. In low-light conditions, a higher intensity may be necessary.

Always refer to the manufacturer’s user manual for specific troubleshooting instructions and contact their customer support if issues persist.

Key Factors to Consider When Choosing a Red Dot Sight for Your Glock 21

When selecting a red dot sight for your Glock 21, several key factors should be considered to ensure that the sight meets your specific needs and preferences. I’m sharing with you some key considerations that you should take into account.

  1. Compatibility
    • Ensure that the red dot sight is compatible with the Glock 21. Some sights may require specific mounting systems or adapter plates for different firearms.
  2. Mounting System
    • Choose a red dot sight with a mounting system that is suitable for your Glock 21. The sight should offer a secure and stable attachment to the handgun.
  3. Size and Weight
    • Consider the size and weight of the red dot sight, especially if you prefer a compact and lightweight setup. The sight should complement the overall profile of the Glock 21.
  4. Reticle Type
    • Different red dot sights offer various reticle types, such as dots, circles, or combinations. Select a reticle that suits your shooting preferences and scenarios. Common options include 2 MOA dots, 3 MOA dots, or larger reticles for faster target acquisition.
  5. Reticle Color and Brightness Settings
    • Opt for a red dot sight with customizable brightness settings to adapt to different lighting conditions. Some sights offer a variety of reticle colors, allowing you to choose the one that stands out best for your eyes.
  6. Battery Life
    • Consider the battery life of the red dot sight. Long battery life is desirable to minimize the frequency of battery changes. Some sights incorporate features like motion activation or solar panels to extend battery life.
  7. Durability and Construction
    • Choose a red dot sight with a rugged and durable construction. Look for sights with shock-resistant and waterproof features to withstand recoil forces and adverse weather conditions.
  8. Lens Clarity and Coating
    • Opt for a sight with high-quality optics, anti-reflective coatings, and scratch-resistant lenses to ensure a clear and distortion-free sight picture. Multi-coated lenses enhance light transmission.
  9. Adjustment Mechanisms
    • Evaluate the windage and elevation adjustment mechanisms of the sight. Look for toolless adjustments or easily accessible turrets for quick and convenient zeroing.
  10. Ease of Use
    • Consider the ease of use and user-friendly features. Look for sights with simple controls, intuitive menus, and features like automatic brightness adjustment or motion-activated illumination.


Choosing the right red dot sight for your Glock 21 is a decision that hinges on a balance of factors ranging from compatibility and durability to reticle preferences and ease of use. As we’ve explored in this article, each sight offers a unique set of features tailored to diverse shooting needs.

As a Glock 21 owner, the satisfaction derived from pairing it with the right red dot sight extends beyond functionality; it becomes a seamless integration of reliability and precision. Choose wisely, considering your shooting style, preferences, and the demands of your intended use. Elevate your Glock 21 to new levels of accuracy and performance.

About the author

The name's Chris. Just a regular dude who loves firearms. I've been shooting since I was a kid. My old man taught me the ropes.

I'll never forget the first time I missed an easy shot on a buck, thanks to a bum scope. The image was fuzzier than my dog's butt. After that, I got obsessed with understanding scopes. What makes the good ones tick and the bad ones trash. After a few years and a few thousand bucks, I learned what separates the winners from the losers. Once I had a good stockpile of knowledge, I launched this site.

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