I have 2 steyrs, one fac and one in 16j. I have a hw barrel on the fac steyr, 60 cmts long. Very accurate barrel with jsb hvy, and the rifle shoots like a dream.
In this video you could see 5 shots group at 50 meters in bench rest. Sadly the video was taken with slow motion and with artificial ilumination at night, and its hard to see the fly of the pellets... its a five shots secuence without cuts. And you could see the movement of the rifle shooting at 22,8 j.
My 16j steyr is the long version, with 55 cmt barrel. Groups well but you need a full clean after 150-200 shots. And you have to put the stripper very carefully in the right position, because if you dont, you will have lots of flyers at 50m.
I have a spare barrel from bsa, with 60 cmts. I have tried it in both guns, and its very accurate. Maybe its a bit long for 16j, but the groups are similar or better than the original barrel, and needs less clean work.