Note that we're talking about "arrowstorms", not individual sniping, in battles like Agincourt. In fact, the evidence suggests that the archers fired volleys on the word of command, "wholly together" in contemporary useage, rather like musketeers later. Except that their weapons had a higher rate of fire and didn't generate clouds of smoke.

A longbowman could shoot an arrow every four seconds or so; call it 15 a minute, a rate of fire similar to that of a breech-loading rifle. Maximum effective range was about 300 yards. At that range dropping shots hit with about 75% of the arrow's initial velocity -- arrows are very ballistically efficient. As the range closed, the archers shifted to direct fire. They stood in a four-deep "harrow" formation, staggered so they didn't mask each other.

And the English armies had elaborate logistical arrangements to collect massive numbers of arrows in England (including orders to pluck every goose in the country of its wingfeathers and send them to the armories), to take them along, and to shuttle them forward to the firing line during battles. That's what a lot of the 'varlets' and 'boys' were doing -- rushing bundles of arrows from the baggage train to the bowmen. Standard practice seems to have been to take two spare bows and several hundred arrows per archer.

At Agincourt there were about 8000 archers according to Curry (rather more than in previous accounts).

That's 2000 arrows a second, 120,000 in a minute, and well over half a million in the time it took the dismounted French men-at-arms to cross the killing ground, a mile of muddy plowed field which had just been rained on.

The target was the 6-8000 men of the French vanguard; their rear, including their crossbowmen, never engaged. They just buggered off after they saw the slaughter of the first echelon, which included most of the higher nobility and leaders.

The French came in a dense column 30 men deep; hence probably 200-300 men across, call it 500 yards of front and 40 or 50 yards deep, 2000 square yards in all.

That's initially, but later they got more densely packed as they crowded away from the archers on the flanks, and the chroniclers record that the ones in the middle couldn't even raise their arms.

That's a target too big to miss, even with 'dropping' fire at long range. So every man at arms would be hit, on average, between 40 and 80 times.

That's 40-80 hits per man by heavy 3 or 4-ounce arrows with hardened-steel bodkin points, travelling at 150-200 fps.

Given the law of averages, some must have been "overkilled" and some lucky; the ones on the outside of the formation in particular would get hit more often and the ones on the inside less.

A substantial number did make it to the English standards, but they were so exhausted, wounded and demoralized that they were easy meat.

It's not surprising that 5000 or more ended up dead, tho' many of those were prisoners killed on Henry's order; however, a lot of those were badly wounded already.

The experience must have had a lot in common with marching forward into machine-gun fire.