Beats any Bismuth load on the pattern board and down range...a full one ounce and safe in older vintage shotguns and any choke...Not all that fond of the the high velocity as far as recoil.
https://kentcartridge.com/us/shotshell/tungsten-matrixAddition: And pure TSS shotshells with the right shot cup are being used in older shotgun with no problems..9's hit like 5' and 6's and the pellet counts are super. Downside is they are crazy expensive....However, I used them in a modern 28 and they were impressive..With only shooting maybe 50-75 shots per year on Pheasants, the price when factored into all the other costs didn't make much difference.
Not sure if they are yet available in 20 Gauge.
Just checked... they are from Apex..They should be able to tell you if they are vintage gun compatible.....