If you are going to shoot in the field, then you are
going to have to shoot from a number of different positions and so you
should be well practiced. But you shouldn't blame the faults on the rifle -
a shift in point of impact when you change shooting position is usually
caused by the shooter.
Shooting low-left from prone is usually poor
breathing technique (quite a common problem if you've just hiked over a
couple of miles of rough terrain with a heavy rifle! Shooting high-right
is often due to 'snatching' the trigger, which is often due to trying to
hold a heavy rifle steady for too long on aim; this can also be linked to
breathing control.
Other factors to take into account are the
trigger pressure (too high and the tendency is to 'snatch') and also that
a rifle will behave differently if it is sitting on a 'hard' rest; it's
usually better to hold the rifle and make use of a sling or a nearby solid
object to brace the shooter against, rather than the rifle.
A 'recoilless' rifle will tend to hide these
defects (possibly in part due to lighter weight).
