I am shooting with a Daystate Wolverine 303 hilite and I found that 60 gr and 55 gr(NSA) are the most accurate.If your barrel is Lothar walther may you can see good results with these grains. For 60 gr speed 870 for 55 gr speed 900. Is remarkable that in 50 meters 60 grains group was very good(better than 55 gr) but in 100 and 150 yards 55 gr are grouping better. I assume that I need more speed for 60 gr.Gun is without any mods. 47 gr results was unacceptable even in 50 meters. Like I was shooting with a shotgun.
Unfortunately I have pictures to post only from 50 and 150 yards . Best groups at 100 yards was 2 -3inches but always with strong enough wind. Not perfect but good enough for me for so far. The photo in 150 yards is with 55 gr. Check in the photo how much better performs 60 gr at 50 yards comparing with 55gr.That is changing in 100 yards and above.