I own also a M25 9MM.Noticed that the groups are better without the bipod, just use a sandbag.Without the silencer gives also better results.Use the JSB pellets. I still have some flyers sometimes.Here a 5 shot 50 meter group.
Have you had a chance to shoot it yet? I've been dieing to hear and see how the work improved your groups.
I only used the ZAB 80Gr slugs, and they performed very bad.Just keep on shooting the JSB .35 at 50 meters.