Roger's correct: Two things control how well a bow "casts" an arrow - energy storage efficiency (SE/PDF) and dynamic efficiency (DE). Straight-limbed longbows are poor in both categories. Not that they don't have their place and they appeal to lots of archers.
The myth that they shoot a heavy arrow more efficiently than a high-performance bow is just that - a myth.
How "forgiving" a bow is has always been a mystery to me. I'm a quant and not much interested in debating subjective matters because they're, well, subjective and therefore very personal in meaning. However, a bow that shoots an arrow weighing "X"-grains-per-pound of draw at 155 fps versus another one that shoots an arrow weighing "X"-grains-per-pound at 190 fps has never seemed more forgiving to me simply because it was slower. At least in terms of vertical misses the faster bow would be more forgiving it seems to me.
Stability is not subjective at all...
Stability is almost the oposit of speed in many cases... High preload in 99% of all bow cases a source of instability. You have to DAM clever to sort out the geom issues, associated with high preload instability.
Lets look at what makes a bow stable.
If you look at the bows centre of gravity, you need the grip infront of that.
For exactly the same reasons why planes with wings below them create a "V" as the lift point is above the aircraft, while those with cheap wings that are stright have, the weight suspended below the wing to keep the plaine stable.
The bows grip needs to be infront of the centre of gravity...ie deflexed
this concept reduces the bow torque induced by release parradox.
The grip needs to be repeatable. Pistol grips are easier to get more consistancy with, this makes a bow a little more forgiving.
must dissagree that stability is subjective. 144 arrows, over 30-90 meters, top scores are shooting recurves and are putting in scores of 1320, where a max score is 10 points per arrow. perfect score of 1440.
get rid of the release hand issues by way of trigger and you can get scores of 1400, so NP stability is VITAL.
Now we need to look at the bow as a whole, to solve two areas of this instability...
look at the nocking point. it needs to be a reliable as possible. It needs to be reliable in two axis, both vertical and horizontal.
Lets look at the horizontal to start with.
as you release the string, it travels in the opposit direction to your release fingers. crossbow latches either lift up or drop down, id pefere a lift up latch, as it drops the string down on to the track makeing sure it doesnt lift over the nock of the bolt.
Note in a bow you dont have the track to catch the strings sideways movement. So where is the first point of resistance.the forward movement of the limb will help pull the string into line, but the limb will be prone to sideways deflection... That sideways deflection of the limb, as seen in W&W top down video, shows the left right deflection of the limb.
This deflection will be enhanced on limbs with little torsional stability, and while this is a problem, its still exagerated with a deep plucked loose vs a clean loose. So a bow that handles the horizontal nock travel well, will be more forgiving of poor release techneques.
Now if you want a techneque to measure this, you can get a bow to full draw, and measure the torque resistance of the grip (dont try this at home as you can pull the bow off the string)
The HH grip was deep which gives a level of depth to help catch the release hand torque. this does need good bow hand techneque, so the grip also suffers by this same token.
The next one is vertical stability.
Vertical stability is how hard the string will resist a up and down movement.
high stress R/D bows are normally very poor in this area, This is where and form issues that lead to a dragging top or bottom finger during release leads to a porpoising effect on the np path. this is due to the two limbs fighting over the imbalance and creates limb flap. Bows that "close" quickly are ones that settle down quickly are ones that have good limb timing, but are also vertically stable. This is a bow where the term "Noodly limbs" applies.
I'll give you an example, The ILF longbow limbs are noodly, untill you use a high brace height where they become "acceptable", BUT ILF recurve limbs are acceptable though a bigger range, which hugely indicates better overall vertical stability.
to measure this you need a little loop attached to the serving, a spring balance to that and with say a 3lbs load, note how much fore and aft deflection of the limb tip do you get...
Bows are nothing but geometry/engeneering and physics. everything can be quantifiably measured if you know where to look.
you need to do some sprint training , and your coach will tell you to stop running like a soccer player, elbows out and bobbing from side to side, if you want speed, keep it all nice and tight and in a straight line. bows are just the same...