kwelhand 2 Posted June 8, 2013 Report Share Posted June 8, 2013 Why Vepr-12 jams with heavy optic mounted on its top rail? I've seen some of the video and it looks like Vepr-12 doesn't like some optics on its top rail. I searched the board and couldn't find the right answer. Any thoughts? Quote Link to post Share on other sites
ec4321 113 Posted June 8, 2013 Report Share Posted June 8, 2013 The problem arises when optics of certain shapes / sizes are placed on the rail in such position that a shell ejecting can hit the optic (think eotech) slowing/stopping/bouncing the eject shell and causing a FTE. There may also be other issues with weight of certain optics in certain positions on the rail since the bolt carrier does rub the rivets as it cycles. I reprofiled the fastner heads and polished them on mine. Quote Link to post Share on other sites
DresNightfire 39 Posted June 8, 2013 Report Share Posted June 8, 2013 The optic position above the ejection port or in front of it during ejection causes the bolt carrier to rub the first rivet of the dust cover, slowing down the speed of the bolt carrier, hence not providing enough power to eject the shell casing. The optic obstructing the shell casing was not the case in the past. Sturmghewehre also talks about this in his Youtube description VEPR 12 video: ... More info on the malfunctions with a sight set forward:Due to the overwhelming number of comments regarding the EOTech failures, I wanted to give you more info about the testing I did. What I can say is that I know for certain the malfunctions have absolutely nothing to do with the EOTech specifically. The malfunctions will happen with Aimpoint Pro's, Comp M2, M3's, and even a Sparc mounted with a metal riser mount. These malfunctions were confirmed by the importer and several owners have contacted me saying they have noticed the same issue.Inside the top cover there is a rivet that holds the rail in place. One rivet in the front, over the bolt carrier, and one in the rear. The one in the front sticks down 1/8th of an inch or so while the rear rivet is recessed. The front rivet contacts the bolt carrier during firing, you can clearly see the marks on it. The carrier jumps upwards upon firing and hits the top cover. As evidence of this, my shotgun will eventually pop the top cover open if I fire enough rounds through it due to the carrier hitting the top cover. It usually takes 5-6 rounds. The importer noticed this rivet and removed some material from it and their shotgun worked with an EOTech in that position. I removed some material from my rivet but I still have the issue. I didn't want to remove too much material. As long as you mount the sight to the rear, every sight I mounted worked just fine without causing any malfunctions. Quote Link to post Share on other sites
thebuns1 4,323 Posted June 13, 2013 Report Share Posted June 13, 2013 ^^^ I think they rub the front rivet regardless of optic or not. Mine does. Quote Link to post Share on other sites
raidersfan_5544 57 Posted June 13, 2013 Report Share Posted June 13, 2013 I think so too... mine does as well. I also remember hearing Papa Z say it was designed like that for a reason. I think it was to help with the alignment of the piston/bolt carrier which helps prevent bc breakage. I can't remember exactly. I wish someone "in the know" would help explain the reason for the larger front rivit a little better. Quote Link to post Share on other sites
DresNightfire 39 Posted June 13, 2013 Report Share Posted June 13, 2013 ^^^ I think they rub the front rivet regardless of optic or not. Mine does. I think so too... mine does as well. I also remember hearing Papa Z say it was designed like that for a reason. I think it was to help with the alignment of the piston/bolt carrier which helps prevent bc breakage. I can't remember exactly. I wish someone "in the know" would help explain the reason for the larger front rivit a little better. Correct, the rivet was purposely created there to allowed better alignment of the bolt carrier during cycling, adding more reliability and minimizing the chances of the bolt breaking (in addition to the bolt rails are there). Rubbing is normal, but with the optic on it rubs even more (causes even more friction, i.e. slowing the carrier rate of cycle). Quote Link to post Share on other sites
WUNDERWAFFEN 21 Posted June 13, 2013 Report Share Posted June 13, 2013 I remember reading that Cobra concluded that the front was larger for the LRBHO. Without it it does not work. Quote Link to post Share on other sites
thebuns1 4,323 Posted June 13, 2013 Report Share Posted June 13, 2013 I remember reading that Cobra concluded that the front was larger for the LRBHO. Without it it does not work. I dont know. On mine, I raised the dust cover, insert an empty mag and pull the charging handle back and mine still locks back every time. lol. 1 Quote Link to post Share on other sites
WUNDERWAFFEN 21 Posted June 14, 2013 Report Share Posted June 14, 2013 I remember reading that Cobra concluded that the front was larger for the LRBHO. Without it it does not work. I dont know. On mine, I raised the dust cover, insert an empty mag and pull the charging handle back and mine still locks back every time. lol. Lol probably took less than 30 seconds to prove that wrong. Kinda related - Has anyone replaced their top rail with the CSS rail? & how did that work out? Quote Link to post Share on other sites
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