Mine has an O ring and a removable vent hole brass thingy.
I would have to say it did not work the way it was supposed to when I got it. Even with paper cartridges that cut the tail off, exposing the powder.
I did not send mine out. What I did was:
Stop using CCI caps and use RWS. Much hotter spark, but still required a couple shots on some cartridges.
Enlarge the flash hole to 1/16"
Do your best to polish the tunnels the sparks have to travel from nipple to vent hole.
Here is a picture of the breech and clean out screw it came with. That little nub you see at 6:00 is the end of the clean out screw, which is supposed to index the brass vent hole.
Being that short, the factory screw isn't long enough to index the brass piece perfectly and it can wiggle. That means the hole the sparks have to travel into could be partially closed off. Major problem IMO.
Plus the sparks can travel past the last 90 degree turn they have to make.
I'm pretty sure that rounded end of the clean out screw is supposed to go halfway across the opening, which is even with the vent hole when it's screwed in.
So I had my buddy build up the end of the screw with his TIG welder, then I gave it a bevel so when the sparks hit it, it helps them go in the right direction. Out the vent hole.
The sparks are entering from the right side traveling left in this pic. Heading right towards ya.
Now it's a joy to shoot. Bang every time. And I've taken to using rolling papers for the base of my paper cartridges.
There is still quite a bit of fouling with that moveable chamber. After several shots it is hard to push the cartridges in all the way. Some swabbing may fix that. I can't say I'm a fan of that floating chamber though. I always wonder how well I cleaned it.
Shameless rifle pic
Three shots at 50yds off a bench.