The Holosun 507K is one of the most popular handgun red dots on the market, and the Glock 43X MOS is probably the most popular optics-ready, concealed-carry pistol available. There's some confusion about whether the 507K fits the MOS slide. We're clearing that up today with a detailed unboxing, review, and installation.
Holosun 507K: Unboxing & Review
The 507K ships in a reusable plastic storage case, with high-density foam inside. The optic ships ready to use, with the lithium-ion battery installed and a rough 25-yard zero applied at the factory. By default, the optic's reticle is programmed to display a red dot and halo.
In addition to the optic, you'll receive the following components:
- (1) Multi-tool
- (1) Warranty card
- (1) Instruction manual
- (2) Sets of mounting screws
- (1) Microfiber cleaning cloth
- (1) CR1632 li-ion battery, installed
The multi-tool is fitted with a T10 Torx bit for tightening the optic's mounting bolts. The flathead end of the tool is used to make adjustments and remove the waterproof battery compartment cover.
The warranty card's QR code can be scanned to register your optic and to redeem the limited lifetime workmanship and parts warranty in the future, if ever needed.
Construction, Coating & Specs
The 507K is machined from a single piece of forged aluminum (7075-T6). It is treated with a hardcoat, matte black anodized finish, like you'd find on a standard AR-15 receiver.
The lens' aluminum housing was made to take some real abuse and can withstand hard impacts. It measures about 3.25mm thick around, and it's over 4mm thick at the corners.
The 507K keeps a relatively low profile, measuring approximately 0.954" in height.
The 507K measures about 0.945" wide and 1.60" long, maintaining a snug and precise fit inside the MOS slide's factory cut-out. The optic is lightweight, thanks to its aluminum housing. It weighs 29 grams (0.06 pounds), adding virtually no weight to your pistol once installed.
The lens provides a viewing window approximately 0.58" wide and 0.77" tall. Holosun machined a cut-out at the rear of the optic that acts as an open rear iron sight. This allows for easy co-witnessing between the optic and the 43X MOS's factory irons, shown below.
NOTE: Using an adapter plate to fit the 507K to the MOS slide will raise its overall height, reducing the ability to easily co-witness with factory irons. We'll cover how to install the optic without a plate in this guide.
Modifying Your MOS Slide for Install
The Holosun 507K fits any slide that is cut for the Shield RMSc reflex sight. The Glock 43X MOS slide is cut for the RMSc. However, four raised indexing posts on the MOS slide prevent the 507K from sitting flush.
Grind the optic mounting posts
An adapter plate can be purchased separately to make the 507K fit the MOS slide. This will raise the height of the optic, obscuring the slide's factory iron sights. To avoid using an adapter plate, the two rear indexing posts can be ground flush with the rest of the slide's optic cut-out. The front posts need to be trimmed 0.3mm to allow for proper installation.
This slide modification is required because the 507K's underside only has two recessed points that will fit with the MOS slide's front post. The rear of the optic's underside has no slide post indexing points.
Cut down the mounting bolts
With the slide modified, the optic will sit flush. However, the provided mounting bolts' threads are too long and must be trimmed. Cut each mounting bolt with a Dremel and cutting wheel so three threads protrude from the bottom of the optic, as shown above.
You can now install the 507K
With the slide prepped and the bolts cut, the 507K can be installed. Use the provided Torx bit tool to hand-tighten the bolts.
Optic Set-Up and Use
The 507K features an adjustable reticle pattern and a "shake awake" feature: When the optic detects movement, the reticle will illuminate automatically. By default, the optic will shut off after 10 minutes of inactivity. All settings and functions are entered and saved using the plus and minus buttons on the left side of the optic.
Choosing the reticle pattern
To cycle through the available reticle patterns, simply press and hold the "-" (minus) button for three seconds. The reticle can be switched between a standalone red dot measuring 2 MOA, a dot and halo, or just the halo. The halo's circle measures 32 MOA. in diameter. For sizing targets, the circle measures 8" at 25 yards and 32" at 100 yards.
Brightness and lock-out
The 507K features 12 brightness settings: 10 daylight and 2 night vision, the latter being almost invisible to the naked eye. To switch brightness settings, press the "+" and "-" buttons. The brightness and reticle pattern can be locked by pressing and holding the "+" button for three seconds. The reticle will blink once to indicate lock-out mode is engaged. Press and hold the "+" again for three seconds to disengage lock-out mode.
Change sleep times / toggle always-on
The sleep mode can be increased to 1 hour or 12 hours, and it can be disabled entirely so the optic is always on. To change the sleep settings, press and hold the "+" button for 10 seconds. Then press and release either the "+" or "-" button to cycle through the 4 sleep settings (10 MINS, 1 HR, 12 HRS, OFF). The reticle will blink with each selection. To save the selected sleep mode, press both the "-" and "+" buttons simultaneously.
To manually turn off the reticle, press both the "-" and "+" buttons simultaneously.
Battery life and replacement
The 507K provides exceptional battery life: With the red dot enabled at brightness setting 6, estimated battery life is 50,000 hours. With the dot and circle enabled at setting 6, estimated battery life is 10,000 hours.
Should the battery need to be replaced, remove the flathead bolt securing the waterproof compartment using the multi-tool. Then slide the battery tray out. The CR1632 battery should be installed with the NEGATIVE (-) terminal facing up.
Zeroing and Adjusting the Optic
The "UP/DOWN" (elevation) and "LEFT/RIGHT" (windage) adjustments provide 1 MOA of adjustment per click. This equates to 0.25" at 25 yards, 0.5" at 50 yards, and 1" at 100 yards. The maximum adjustment range is +/- 50 MOA. To rotate the turrets, use the flathead tip of the multi-tool.
Always make adjustments in the direction you want point of impact to shift. For example, if your round lands low and left of the target while zeroing, adjust the turrets "UP" (counterclockwise) and "RIGHT" (clockwise).
Need more help? Here's how to zero a red dot sight!
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