I can’t speak for the MKA 1919 except that the guy running it in our matches doesn’t seem to have any trouble from his, aside from still trying to figure out the best way to handle slug select portions of stages when loading from box mags.
The Vepr 12 doesn’t have any gas adjust, auto or manual. Whoever initially reported that was mistaken or was deliberately misleading. They are simply full open all the time. They do feature some durability improvements in the way the gas puck and oprod interface over the Saiga 12 though.
From my brief experience, I’d only be concerned with the lack of gas adjust if I planned to shoot a lot of 3" buckshot or comparable. All of the 2 3/4" stuff I’ve fired seems fine. Function is still fine on the 3" stuff, I’m just concerned I’m beating the shotgun to death. I’ll probably buy and modify a spare gas puck with some grooves to allow some gas blow-by for use with 3" shells.
Magazines aren’t that bad, so long as you don’t insist on trying to find Russian mags. Russian 8 round mags were coming in at around $99 and they’re even harder to find now than initially.
SGM makes 12 and 10 round mags that are ranging in price from $38 to $50 per. They are made so they can be cut down to 10, 8, 5, or 3 rounds by the end user. You just cut the mag and slip the floor plate on the next rib.
Any of the aftermarket Saiga 12 mags that I’ve seen (AGP and SGM’s rock-in mags) can be modified to work with a Vepr 12 in a few minutes with some filing. The bolt hold-open won’t be activated, but there may be work-arounds for this if you’re handy.
The major changes with this shotgun over the Saigas are that they run out of the box with everything, they come with AK-type rifle sights, they come in pistolgrip configuration, they feature a very well-designed bolt hold-open that features an external bolt release as well as an external hold open button, and most importantly, the magazines are much, MUCH easier to load on a closed bolt.
The major advantages over other shotguns I’ve run are the super fast reloading and bolt hold-open. I can operate the controls, shoot, and reload mine as fast as an AR. Mag changes are very slick.
I’m a rifle/pistol shooter who didn’t like shooting shotgun. I love shooting with this shotgun.
ETA: It has been confirmed by one of our Russian friends that Vepr shotguns can use Saiga 12 bolts and carriers, though the Vepr 12 oprod would need be be swapped onto the Saiga carrier. The handguards and pistol grip are AK/RPK compatible (though the gas tube is unique) and they accept any stock that’ll work with an RPK- regular AK stocks need some fitting to fit in the receiver.
These Vids show off the shotgun pretty well:
Vepr 12
SGM Vepr 12, 12 round mags