I originally purchased my VEPR-12 in late 2012. I reviewed the gun for RECOIL Issue 12 that was published in early 2013. I did not initially have problems with Slug Accuracy using the polymer rail attached to the hinged top cover, over the course of time of using the VEPR-12 I found that the Zero would shift after cleaning. The groupings were not adequate to hit some slug targets at the MGM Ironman 3 Gun Match. When the mechanical accuracy of the shotgun is 8″ at 50 yards, and the plates on a spinner are 8″ and 10″ across, hitting it was more a matter of luck than skill.
In May of 2015, I wanted to resolve this problem before attending the Ironman 3 Gun Match that year. I asked the bossman at KE Arms for help modifying my VEPR-12 to be more accurate. I needed a rail mounted to a part of the gun that would not move and would allow me to leave the optic in place while cleaning the gas system. The gas system on a VEPR-12 must be cleaned every 200-300 rounds for reliability.
We removed the rear sight and milled that area flat. We then sized a piece of picatinny rail to drop down into this space and drilled and tapped the shotgun to hold the rail in place.
The aluminum rail drilled and tapped into the shotgun made for a much more rigid mounting point for the optic.
Update May 2016: One problem that remained though was that the lever to remove the top handguard and access the gas system for cleaning was blocked by some optic mount combinations. When I switched to this Aimpoint micro, I had to make another change.
I removed the factory lever and replaced it with a nut and bolt secured by a cotter pin. The optic could now stay in place for routine cleaning and maintenance.
Using this optic mount dramatically improved slug accuracy to having 2.5″ Groups with good slugs and and 4″ groups with cheaper slugs at 50 yards. Kalani Laker asked me at a match not long after doing this work, what I thought the best things to do to improve the VEPR-12 for competition were. I recommended the optic rail mod as the most important upgrade to do. This feature would be incorporated by Dissident Arms into the KL-12 used by Kalani. It is also available as an upgrade to your existing shotgun.
Updated March 2019: I retired my VEPR-12 after the Hard as Hell 3 Gun Match 2017. With 5 years of use and 5000-6000 rounds fired through it, it started experiencing reliability problems and breaking internal parts (fire control). For the 2 matches a year that I do Trooper 3-Gun as of this post (March 2019) I am using the Mossberg 590M. For SMM3G I shoot in Stealth Division with my Beretta 1301. Otherwise I shoot Rifle only and 2-Gun Matches 3-4 times a month in Arizona and don’t need a shotgun at all.