Captain, I have a similar style Svarog Zveroboy tailwad slug,too. No success yet. This AS Grizzly is supposed to shoot from a rifled barrel. Rifled choke...? I'm finding out.
I tried three more different wad colums. Same load.
Two of these made round holes @ 25 meters. The one with a gas seal/nitro card/two tall "cardwads" (what do you call those black,hard things?) keyholed big time.
This is the same (russian?) cushion as yesterday, I only substituted the cork with this black "whatdoyoucallit?" Got round holes and a group this way. The other ,(italian) cushion, worked with 28 and 20 corks.
A blizzard / storm is coming with a foot of snow now, I'm glad I got this test done before it hits.
I will try a slower powder (VV 3N37) next but first shoot these two 50 m.
I may dump this column, it's very hard to get that 28 gauge cork to stay in the cup. It keeps slipping back up and out. But you need it in there for support,in this case under a 20 gauge cork.
All in all,this is pretty crazy stuff. If / when you find working components, you run out of them and can't find them any more...