I get annoyed at these questions as well, but, it is a valid question to learn from. I have run free mentoring programs for 7 yrs now and put about 100 people through my camps each year. I get this question often, along with what gun/camo/3" or 3.5"/boots/socks should I buy - what did our grandparents do..without this Gucci kit?. I see people who are in $1000, under armour outfits, with $2000 guns. They cant shoot, nor know how move or understand the wind, that's why I mentor. No bad questions ever, just people learning.
I pull out my Savage Axis 1 (I have 4 different calibers, <$500 guns), and show pictures of my groups at 100 to 400 yards (1'-3" MOA). Most new hunters don't have the experience, nor spend enough time on the range to develop long range shooting skills and BE consistent. This leads to teaching shootings that I learned in the army as a sniper and as part of the rifle team. My Mentor was Capt Keith Cunningham in the early 1980's. Every hunter should spend more time on the range, every hunter should know the characteristics of each rifle they own and bullet performance (by weight). You only get that by.... shooting lots. (also why I reload)
The shooting principles that I learned are:
Comfortable Natural position - take up a position, look through sights, close eyes - relax body, open eyes and see where you are pointing, make small body adjustments, close eye - open, adjust until no strain is left in holdover or sight picture. At this point you are naturally align with target. This is the most important principle to follow and the next 3, everything translates errors from this point, and they increase exponentially the farther you shoot out.
Breathing - Once aligned - take up aim point and breath naturally. Observe the rise and fall or left and right movement of crosshairs. It should be rise and fall. On a typical shot, I breath 3 breath cycles and hold breath at rise of 3rd one at mid point.
Trigger Control - Squeeze the trigger, index of knuckle, fingertip pads, it don't matter. Squeeze slowly until rifle fires. Continue to hold trigger down and observe through scope. Repeat this procedure for every shot.
Follow through - While trigger is still held back, slowly release trigger until sear clicks, continue to observe.
To the OP, if you do this and do it often, you will always hit your shot at 400M. If you don't do this, then stick within 200M as your POA and MOA will work for most shooters if not snap shooting.
Remember - Our grandfathers had denim pants and red and black hunting coats. The only thing ONLY, that matters with all large game in wind direction and movement.
Remember - As others have posted the average range is 150-200M that most game is taking across Canada. Shoot to that distance, train at that distance, practice at that distance, practice with the bullet weight you fire at that distance.
Then go out and shoot your 400M moose.