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OVERVIEW

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I have purchased both the Holosun HS503c and the Holosun HS503GU Both are awesome red dot sights aka RDS' that are very similar but have a



few differences.



These differences being:



1. POWER

503C: Can be powered by either the solar cell or a CR2032 battery

503GU: Can only be powered by a CR2032 battery



2. DIGITAL BUTTONS

503C: Because the 503C has a solar panel on the top of its body, the digital buttons on the right side of the body

503GU: The digital buttons on the 503GU are on top of the red dot body



3. BATTERY

503C: Has a battery "tray/drawer" that pulls out and is secured by two micro-sized Philips screws (which can be lost easily)

503GU: Has a battery in a round, screw-on turret (which I prefer)



4. TURRETS

503C: Does not have raised shrouds that surround the windage and elevation turrets

503GU: The U in the "GU" signifies that raised shrouds surround the windage and elevation turrets on two sides (front & back)



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BUILD QUALITY & MOUNTING

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While this is a budget friendly optic, its build quality is exceptional for the price point. While the build quality of an Aimpoint or

Trijicon may be superior than the Holosun optics, the Holosun optics are no slouch in this category.



I have the 503C and the 503GU installed on different SBRs. They have been tossed into my range bag, then into the trunk of my car numerous



times to and from indoor and outdoor ranges in temperatures ranging from 30f to 100f. Not once during my 6 months of ownership has my

original 50/200 zero strayed or been lost on either of the RDS'.



Both include a low mount (for shotguns and AKs) and 1/3 Co-witness mount. The mounts are not top of the line, but they work nicely. I have



replaced my mounts on both the 503C and the 503GU with LaRue QD mounts.



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POWER & BATTERY LIFE

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503C: The 503C does not have the AUTO ON/OFF feature that the 503GU has. The 503C has two power modes, first being AUTO MODE and the

second being MANUAL MODE.



AUTO MODE: (Solar & Battery power)

a) Sight is always in auto mode unless specifically switched to manual mode.

b) While in auto mode, the brightness of the reticle is automatically adjusted to match ambient lighting. The brighter it is, the higher

the dot intensity.

c) If lighting is low enough, the sight will automatically switch to the battery. While running on battery, you can adjust the reticle

brightness using the "+"and "-" buttons to switch between levels 3, 4, or 5.

MANUAL MODE: (Battery power only)

a) Press down the "+"button for 3 seconds to enter into Manual Mode.

b) Brightness adjustment: There are 12 settings for reticle brightness level under manual mode. The default brightness is at 7 when the

device is switched to this mode. The brightness can be adjusted as required by pressing the "+"or "-" to increase or decrease the

brightness level, one press for one change in brightness level.

c) Switching back to auto mode: Simultaneously press the "+"and "-"buttons to switch to auto mode. The device will also switch

automatically from manual mode to auto mode if there.



503GU: While the 503GU only has one power mode, which is battery powered, it offers an AUTO ON/OFF function that is not on the 503C model.



The automatic on and off is based on motion. It will turn itself on when motion is sense and it will turn itself off after 10 minutes of

no motion, or you can manually turn it off by simultaneously pressing the "+"and "-"buttons.



BATTERY: Both optics are rated for 20k hours at mid-brightness and 50k hours for single 2 MOA red dot at mid-brightness.



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ZEROING & STAYING TRUE

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Adjustments are in 1/2 MOA.



I've zeroed several optics and RDS' in the past and was easily able to zero both Holosun optics in 5-7 rounds. The Elevation and Windage

adjustments are crisp and I can feel each individual click which is great. Each click for both windage and elevation is 1/2 MOA

adjustments.



After firing several hundred rounds through both my SBRs with the 503C and the 503GU, storing my SBRs, traveling with my SBRs, then

heading back to the range and so forth, both the Holosun optics stayed true to its zero and I have not had to adjust it from my original

zero of 50/200.



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WINDOW, RETICLE, & BIRGHTNESS

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The lens objective on both the 503C and the 503GU is 20mm. The glass is clear with little to no blue/green tint and handles sun glare

extremely well during my bright outdoor shooting adventures. The reticle brightness even goes plenty bright to shoot outdoors in the

bright sun. I seriously have no complaints on how it handles the sun. Both (to my eyes) seem to be a true 1x for magnification.



Both the 503C and the 503GU have the same reticle options:



Option A: 65 MOA Circle with 2 MOA dot

Option B: 2 MOA dot only



Per Holosun both the 503C and the 503GU are parallax-free with unlimited eye relief.



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SPECIFICATIONS

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503C SPECS:

Reticle: Option A: 65 MOA Circle with 2 MOA dot - Option B: 2 MOA dot only

Light source: LED

Parallax: Parallax free

Eye Relief: Unlimited

Coating: Multi-layer coating for all lens.

Magnification: 1X

Battery: CR2032

Battery Life: 20,000 hours for circle dot at mid brightness setting 50,000 hours for single dot at mid brightness setting

Brightness Setting: 9 DL & 2 NV compatible

Housing Material: Aluminum

Housing Finish: PEO/MAO housing finish

Housing Color: Black

Storage Temperature: -40C to 70C

Working Temperature: -10C to 50C

Waterproof: 1m

Dimension: 133X54X72mm

Weight: 120g



503GU SPECS:

Reticle: Option A: 65 MOA Circle with 2 MOA dot - Option B: 2 MOA dot only

Light source: LED

Parallax: Parallax free

Eye Relief: Unlimited

Coating: Multi-layer coating for all lens.

Magnification: 1X

Battery: CR2032

Battery Life: 20,000 hours for circle dot at mid brightness setting 50,000 hours for single dot at mid brightness setting

Brightness Setting: 10DL & 2NV Compatible

Housing Material: Aluminum

Housing Finish: MAO Finish

Housing Color: Black or Flat Dark Earth

Storage Temperature: -40C to 70C

Working Temperature: -10C to 50C

Waterproof: 1m

Dimension: 66x64x37mm with high mount

Weight: 138g