ABOUT THE PARALLAX
The Parallax developed through several phases going back to 2022.
It began as a simple PLA riser bolted to a spare ADM QD T1 mount—nothing fancy. The goal was to validate optical centerline height and usable objective diameter at the furthest practical position along an AR-15 upper receiver.
The concept began with three competing architectures:
a forward, separate picatinny riser
a combination clamp mount
a bridging spacer
The combination clamp mount would have been the tankiest option, but also the heaviest and most expensive.
The forward tower was roughly the same weight, but more flexible. It could easily interface with a wide range of prism optics, depending on how much height allowance was built into the design.
Ultimately, I decided the Primary Arms SLx 3X and 5X MicroPrisms were the right optics for the application. At the time, there were fewer viable alternatives, and the preferred 1.54” prism centerline drove a required 2.7–2.8” optical centerline for a piggyback T1-pattern red dot.
An early MJF nylon tower prototype lived on my 11.5” carbine for over a year. Surprisingly, it held zero for roughly twelve months despite being regularly thrown into the back seat repeatedly, carried in and out of vehicles, and used to validate this height.
A separate MJF spacer concept spent time mounted in an M14 sight pocket. The 5X prism ultimately isn’t well-suited to that platform even with an adjustable stock, but if a system has to adapt to something odd, the M14 would be a good place to start, as it is the most common rifle here that doesn’t have a good picatinny ecosystem for achieving this stack.
After revisiting the spacer geometry, I found a cleaner approach. That second major revision became the production design. The spacer didn’t change much, but the contoured sun shade literally filled the gap (physical and conceptual) I was seeing in the system.
DESIGN GOALS
The goal of the Parallax is simple: produce an optical stack that does the following:
Saves money by using sufficient-quality optics
(SLx MicroPrisms and Holosun 403/503-class red dots)Prevents objective lens glint without honeycomb or similar ARDs
Allows quick lens wiping to clear rain and fog diffraction
Achieves the lowest usable RDS optical centerline relative to the prism
Keeps the prism at a preferred position on western carbines (AR-15 and similar)
Supports red dot sunshades (hence the #5-40 threads up front)
Mounts to the included Primary Arms base or alternatives
(i.e. ADM QD mounts and carry handle adapters, because why not)
COST AND WEIGHT CONTEXT
Optics:
Primary Arms SLx 5X MicroPrism — ~$400, ~7 oz
Holosun 403 / 503 / ARO, Vortex Crossfire II — ~$120–220, ~3 oz
Griffin Armament GPS1X — ~$345, 6.3 oz
(astigmatism taxes are real)
Parallax system:
Parallax spacer, shade, and hardware — ~$200, ~5 oz
Total system weight:
~15 to 18 oz, depending on optic choice
COMPARISON TO ACOGs
The 5X configuration (recommended) lands closest to the Trijicon TA55 (5.5×50) and TA02 (4×32 LED).
For reference:
TA55: 25.6 oz
~$1,700 street / $2,328 MSRPTA02: ~17.5–18 oz
~$1,200+ street / $1,750 MSRP
A comparable Parallax 5X build comes in around ~$800, saving $400+ and several ounces versus a TA55-based setup.
A GPS1X-based build lands at a similar weight for under $1,000.
It may cost way more than a Chinesium mount on Amazon, but it employs Americans and saves you money.
