I use that setup in my Omega with BH209 powder & cci mag primers. I had same results The HPH-24 sabot aka blue sabot made for Barnes Spit Fire T-EZ. I use the 250 grain bullets tho. Sounds like the 290 with that sabot do the same thing punch the same hole. 1 shot on clean 3 shots on dirty barrel I only had maybe 2 or 4 16ths of a inch movement from the original bullet hole making it a bit bigger. If it was not for that small movement I would not be able to tell if I hit the target. I have never had that happen to me with a muzzleloader or well any gun punching the same hole that close. That blue sabot supplied from Barnes you can buy cheaper at Sabots Muzzleload Magnum Products Blackpowder-sabots blackpowder accessories & projectiles
50 Cal. Rifle .451 - .452 Bullet Black HPH/24 Same sabot but its black in place of blue. This is from Barnes site showing the sabots used as packaged Best Accuracy For Your Muzzleloader | Barnes Bullets
I buy the bullets from Barnes in bulk with no sabots much cheaper then the package of em supplied with sabots. I then go to MMP to get the sabots very cheap to buy.
I think Hunting Man has been playing with them sabots bullets also.