57K said:
Fountain E. Conner said:
The statement about 158s being lower in recoil than warm loaded 125s is a bit dubious and there's an easy way to compare the 2. The simple calculation for power factor. Take the example of JHPs loaded close to standard pressure for the .357 Magnum at 35,000 PSI. Just multiply the bullet weight by velocity and divide by 1000. Simple as that. If a 158 gr. JHP comes close to the typical factory rating of around 1250 FPS from a 4" barrel: 1250 x 158 = 197500 / 1000 = 197.5 Power Factor. For a comparison, just take the number before it's been divided by 1000 and divide it by bullet weight to determine how much velocity it will need for the same PF and recoil close enough that your hand will never know the difference: 197500 / 125 = 1580 FPS where most defense loads are rated around 1450 FPS from a 4" barrel. Higher muzzle-blast? More than likely and why you want loads made specifically for defense if that's the intended use
Yes, but power factor is
NOT muzzle energy and is not linear with muzzle energy...and muzzle energy is the item of interest in determining the
total recoil. Power factor is nothing but a convenient "shortcut" that action shooters came up with because calculating actual muzzle energy would have been a pain in the backside back when action shooting was getting started. (Also, PF actually aligns more closely with the ability of a bullet to take down a heavy object, like a falling steel plate or a popper, than does muzzle energy, where a fast moving bullet without much mass may be easily deflected.)
In the power factor calculation bullet weight and velocity are "equal" in importance. The power factor increases linearly with bullet weight and linearly with velocity. However, in a muzzle
energy calculation the ME goes up linearly with bullet weight but
exponentially with velocity.
So, if you have a heavy slow bullet and a light fast bullet that
make the same muzzle energy from a given weapon then the
total actual recoil energy has to be pretty much the same and that's basic physics - if you don't believe me you can take it up with Einstein and his buddies... :) . (Total actual recoil being the actual rearward force that is the "equal and opposite" reaction to the acceleration of the bullet - the
perceived recoil is modified by all kinds of things - how far the recoil axis is above the support axis, how much recoil can the inertia of the weapon absorb before it begins moving, how fast does the total recoil impulse last, how far can things move to absorb recoil energy, etc.)
So, for a given muzzle
energy there is the same amount of total recoil ... and if the platform (gun, shooter, etc.) is identical then the lighter bullet will manifest whatever recoil is not absorbed by the inertia of the weapon over a shorter time period - i.e. more like getting punched than shoved. It is this spreading of the total recoil event over time (and motion) that makes it possible for a gun and shooter weighing a total of 200 pounds to fire a bullet with a muzzle energy of 800 pounds without feeling like they've just tried to catch a swinging wrecking ball...
The action shooter guys like heavier bullets because they actually get
two benefits. They get the benefit above, plus they can make their power factor with lower muzzle
energy - and thus less total recoil as well as less perceived recoil. Take the case of guys shooting 9mm in IDPA. To make the required PF of 125 with a 115gr bullet requires a velocity of 125,000 / 115 or 1087 fps. Making the same PF with a 147gr bullet requires a velocity of 125,000 / 147 = 850 fps. Now, let's look at the muzzle energy of those two loads. The 115gr bullet at 1087 fps has an ME of 302 ft/lbs. The 147gr bullet at 850 fps has an ME of 236 ft/lbs. That's about a 22% decrease in total
actual recoil.
But, of course, the OP doesn't have to take my word for it. He can shoot some defensive 125gr loads and defensive 158gr loads of about the same muzzle energy and decide for himself... :)
