Mounting a GL on the rifle/carbine is useless.
1) You get a 5lb weight added all the time, for a small amount of actual usage.
2) The GL (and it doesn’t matter what type) makes holding the weapon for any decent shooting very awkward (even worse with the M203A1 Colt Canada mount).
3) In the event of a casualty, you need to recover both rifle/carbine and GL to get the GL.
GL’s should be setup in a stand alone configuration. This allows it to be used when needed and stowed when not.
Ammunition for the GL should not be integrally affixed to the vest, etc of the Grenadier. It should be on a bandolier/belt solely for 40mm storage. That way it can be removed and recovered quickly from a combat casualty.
If the ammo is anything like the HiCar ammo down here, it is capable of excellent accuracy, with extremely low standard deviation in muzzle velocity. Minute of angle results out to 500m should be possible with a capable shooter. Precision effects out to 800m should be very possible with good shooters (albeit not necessarily combat conditions).
Just with an EOTech RDS I was able to consistently hit LaRue steel poppers out to 800m with an 11.5” Sons of Liberty MCAR system.