61 Minute of Angle Zero Shift with Vortex Viper Red Dot Sight

1911 vs Glock. The answer is obvious...
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Mike s
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I decided to get a RDS for my Glock 19 a couple years ago, but didn't really put many rounds through it since it wasn't my every day carry gun. Other than using it for the DPS' First Responders Course, it was basically just used to familiarize myself with RDS'.

Last October I began training with it in earnest to prep for one-handed shooting in anticipation of support-side shoulder surgery in January, as I'd be in a sling for 6 weeks and a bit gimpy while doing physical therapy for the next couple months.

One of the downsides of the design of the Vortex Viper RDS is that you have to remove the sight to change batteries, but that critique isn't unique to this one, as the Trijicon RMR has the same design. I had anticipated a slight zero shift when remounting to the gun, but the three or four times I changed the battery the zero was still on the mark.

I assisted another instructor at his range in April, & we were doing a little shooting before his students arrived. His steel targets are set up at 25 yds, & I was missing by a wide margin low & right. The Viper RDS was zeroed at 36 yds, & I was accustomed to knocking down 6" plates at that distance. After I looked intently thru the sight, I could tell that the red dot was nowhere near aligned with the iron sights, so the RDS came off, & I've gone back to iron sights till it's replaced by something other than a Viper RDS.

That was in April, & I put off returning it to Vortex till now. I did a quick video last week to document how far off the zero had shifted, so I could clearly articulate the issue when filling out the return form. At 36 yds, the rounds weren't hitting the target backer; at 25 yds I was able to measure the shift from Point of Aim to Point of Impact as 16" to the 4 o'clock. That's a shift of a little over 61 MOA, and was a bit eye opening. According to a couple gun forums, mine isn't the only Vortex Viper RDS to lose its zero, but the other didn't specify how much theirs had drifted.

I'm quite certain Vortex will make good on it, but just a fair warning to anyone using ia Viper RDS as part of their EDC. It would be catastrophic to have to use it for self defense, and if beyond contact distance potentially miss your threat & put an innocent third party at risk.

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Bitter Clinger
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Interesting post, thanks. Would love to hear what Vortex has to report upon repair / return of the optic.

I have been running a Vortex VENOM on a full size Springfield XDm 9mm for a number of years, thousands of rounds downrange, throw it in my backpack and take it on trips and have never experienced any issues. Not aware of any technical differences between the two that might account for the problem you encountered.

Vortex claims that the Venom is suitable for long gun as well as pistols, while the Viper is designed for pistols only. Up till now I had always thought that was basically only due to physical size and no other characteristic.
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Mike s
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I'm thinking it may be a problem with both the Viper & the Venom, as I found a couple blog posts citing a similar issue with the Venom. Heck, there were even a couple 1-Star reviews on Vortex's website that cited loss of zero for the Viper.

I'm willing to bet that most of their RDS' are good to go like your's seems to be, with a couple lemons here & there.

It went back to Vortex in the mail yesterday (they provided a prepaid shipping label, which was nice 👍), so I'll update later when I get the replacement & run it for a bit.
Mike s
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So, it turns out that the glass had actually shifted a little bit within the housing of the Viper RDS, which in turn pushed the red dot askew resulting in the drastic shift in POI. I'm glad the Vortex Rep who called me actually took the time to look it over while we were on the phone, because the guys in the shop thought it was just zeroed way off.

When the rep who called me commented on how the finish looked scuffed up on the front, I explained that I had been doing alot of one-handed shooting in the 6 months prior to the zero shift, racking the slide (by using the optic) against the holster, belt, pocket, jeans, etc. That's when he took a closer look and noticed that the glue that seals around the glass & housing was flaking off, then realized that the glass was slightly shifted.

Good news is that I asked them to replace it with the Defender-CCW, their newest RDS, & they did. Both RDS' are listed at the same MSRP, but supposedly the Defender-CCW is built more solid (and, the battery is top-loading so no need to remove the RDS to change batteries).

I plan to run a couple thousand rounds thru this one & make sure it shakes out well.
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Bitter Clinger
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Thanks for the informative follow-up post! Sounds like either an engineering material selection error or a manufacturing process procedure failure.

I also have the Defender optic mounted on a Springfield XD-M Elite 10mm, so will be watching for the results of your after-action range report. Much appreciated!
Menachem Begin to Joe Biden (1982): I Am Not A Jew With Trembling Knees. I am a proud Jew with 3,700 years of civilized history.
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