Just received my M3 today. Threw a scope on it and topped off the bottle. Took about 10 shots to sight in at 25 then 50 yards. Never cleaned the barrel and shot my first 10 shot group at 50 yards with (JSB EXACT Kings 25.39) pellets. 
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Did a little more shooting at 50 yards. Still haven’t touched any factory adjustments. Shooting over my Lab Radar shows the JSB Exacts (25.39) running at 890 f.p.s. So far I have about 150 pellets through the M3.
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Shooting with a rear bag and front rest off the bottle. It was fairly calm out so I didn’t set up any wind flags. I noticed if I add a little cheek pressure it will give me vertical groups. Also shooting off the bottle and not a flat stock the gun wants to rotate in the bag when shot so I need to hold on to it and pull it back into my shoulder.
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The model I have is bronze with 600 mm barrel. I may update the scope for something with finer crosshairs and adjustable instead of using the holdover reticle. Maybe the Athlon. Would also like the barrel tuner when they become available.