I got a MP10 and am now really happy with it. The trigger sucked but I replaced it with a TTU 2-stage.
I had some function problems out of the box with surplus 7.62... not powerful enough to operate reliably and short stroked. Some commercial .308 seemed to work fine, one other was too weak.
None of the ammo I tried (Rem Core-Lock, some Federal load) shot very accurately in my rifle. Not even Black Hills match (which incidentally had some pressure signs and blew a primer, tieing up the gun pretty bad). I recall the best groups were in the high 2 MOA range up to maybe 4 MOA. That is using a 14x Leupold. I figured the light barrel just wasn't going to be a shooter.
Then I tried a handload in it. WCC 05 brass, SMK 168 grains @ 2.800", CCI LR, and 42.0 grains of Varget. I couldn't believe it. I shot several consecutive 3 shot groups to zero with this load and they were all sub MOA, and that was with a red dot on it (Aimpoint M4S). Same load shot really well in my M1A on the same day too.
Function was perfect.
So I need to rescope and try shooting the ARFcom sub MOA all day challenge (5 consecutive 5-shot groups at 100 yards) and see how it does now.