I'm interested in two bullets of 125 grain and 140 grain masses. They're both of the same type and manufacturer. Barnes TAC-XP 125 gr. and Barnes XPB 140 gr. I don't have either of these bullets yet, and I haven't actually shot them. Instead, I calculated the following.
Gun Mass, 1 pound
Bullet Mass, 125 grains
Powder Mass, 5.8 grains
Muzzle Velocity, 894 fps
Muzzle Energy 222 ft.lbs
Power Factor, 111.75
Recoil Impulse .62 (lbs.sec)
Recoil Velocity 20.11 (fps)
Recoil Energy 6.28 (ft.lbf)
or
Gun Mass, 1 pound
Bullet Mass, 140 grains
Powder Mass, 5.43 grains
Muzzle Velocity, 843 fps
Muzzle Energy 221 ft. lbs
Power Factor, 118.02
Recoil Impulse, .64 lbs.sec
Recoil Velocity 20.74 fps
Recoil Energy 6.68 ft.lbf
As I expected, the gun's recoil impulse and velocity with the heavier bullet is greater when muzzle energy is equivalent.
I read that the reverse is often the case when considering "power factor" instead of muzzle energy. I understand power factor is only really relevant within the context of shooting sports rules, but out of curiosity, I calculated a load with equivalent power factor:
Gun Mass, 1 pound
Bullet Mass, 140 grains
Powder Mass, 5.08 grains
Muzzle Velocity, 798 fps
Muzzle Energy 198 ft. lbs
Power Factor, 111.72
Recoil Impulse, .61 lbs.sec
Recoil Velocity 19.59 fps
Recoil Energy 5.96 ft.lbf
Not surprisingly, the equivalent power factor load produced less muzzle energy and less recoil energy, as well as lower impulse and velocity. Those power factor rules really favor the big slugs.
While I haven't tested these. They were both tested by Luckygunner.
Cartridges loaded with the 125 grain bullet produced:
median velocity 1426 fps
median penetration, 16.7"
median expansion, 0.65"
Catridges loaded with the 140 grain bullet produced:
median velocity, 1171 fps
median penetration, 17.1"
median expansion, 0.66"
The 140 grain bullet was actually tested in 1 cartridge and 2 different guns, and the 125 bullet in 3 different cartridges in 2 different guns, but I chose to compare the two that were similar in penetration and expansion. They are Barnes' own cartridge loading for the 140 gr., and Buffalo Bore's cartridge using the 125 gr., both shot from the Kimber with a 2" barrel. Comparing the penetration of the two five shot strings, they were very similar. But how would the recoil compare if the cartridge were loaded to achieve these similar results in the same gun like this?
Using an arbitrary but equivalent gun weight and estimated powder masses:
125 gr.
recoil impulse, 0.92 lbs.sec
recoil velocity, 29.75 fps
recoil energy, 13.75 ft.lbf
140 gr.
Recoil impulse, 0.85 lbs.sec
Recoil velocity, 27.35 fps
Recoil energy, 11.62 ft.lbf
Even if my powder mass estimates are very far off, it doesn't change the result of the lighter bullet producing more recoil impulse, velocity, and energy.
Since the heavier bullet produced very slightly more penetration and expansion, it's fair to say that the performance was at least equivalent in a practical sense and we can't easily conclude that it might not have been quite as good as it appears.
It's interesting to note that it achieved these functionally equivalent results with considerably less muzzle energy, and even slightly less power factor.
125 gr, 565 ft.lbs muzzle energy
140 gr, 426 ft.lbs muzzle energy
125 gr, 178.25 power factor
140 gr, 163.94 power factor
While calculations suggest using the lighter bullet to achieve an equivalent muzzle energy will result in less recoil effect, they also show a heavier bullet will result in less recoil for a given power factor. Actual testing shows the heavier bullet achieving near equivalent penetration and expansion using lower muzzle energy, lower power factor, and with lower recoil effect. Fascinating.
My explanation? I suspect the lighter bullet is expanding more rapidly. Essentially, it's popping the chute earlier.
Gun Mass, 1 pound
Bullet Mass, 125 grains
Powder Mass, 5.8 grains
Muzzle Velocity, 894 fps
Muzzle Energy 222 ft.lbs
Power Factor, 111.75
Recoil Impulse .62 (lbs.sec)
Recoil Velocity 20.11 (fps)
Recoil Energy 6.28 (ft.lbf)
or
Gun Mass, 1 pound
Bullet Mass, 140 grains
Powder Mass, 5.43 grains
Muzzle Velocity, 843 fps
Muzzle Energy 221 ft. lbs
Power Factor, 118.02
Recoil Impulse, .64 lbs.sec
Recoil Velocity 20.74 fps
Recoil Energy 6.68 ft.lbf
As I expected, the gun's recoil impulse and velocity with the heavier bullet is greater when muzzle energy is equivalent.
I read that the reverse is often the case when considering "power factor" instead of muzzle energy. I understand power factor is only really relevant within the context of shooting sports rules, but out of curiosity, I calculated a load with equivalent power factor:
Gun Mass, 1 pound
Bullet Mass, 140 grains
Powder Mass, 5.08 grains
Muzzle Velocity, 798 fps
Muzzle Energy 198 ft. lbs
Power Factor, 111.72
Recoil Impulse, .61 lbs.sec
Recoil Velocity 19.59 fps
Recoil Energy 5.96 ft.lbf
Not surprisingly, the equivalent power factor load produced less muzzle energy and less recoil energy, as well as lower impulse and velocity. Those power factor rules really favor the big slugs.
While I haven't tested these. They were both tested by Luckygunner.
Cartridges loaded with the 125 grain bullet produced:
median velocity 1426 fps
median penetration, 16.7"
median expansion, 0.65"
Catridges loaded with the 140 grain bullet produced:
median velocity, 1171 fps
median penetration, 17.1"
median expansion, 0.66"
The 140 grain bullet was actually tested in 1 cartridge and 2 different guns, and the 125 bullet in 3 different cartridges in 2 different guns, but I chose to compare the two that were similar in penetration and expansion. They are Barnes' own cartridge loading for the 140 gr., and Buffalo Bore's cartridge using the 125 gr., both shot from the Kimber with a 2" barrel. Comparing the penetration of the two five shot strings, they were very similar. But how would the recoil compare if the cartridge were loaded to achieve these similar results in the same gun like this?
Using an arbitrary but equivalent gun weight and estimated powder masses:
125 gr.
recoil impulse, 0.92 lbs.sec
recoil velocity, 29.75 fps
recoil energy, 13.75 ft.lbf
140 gr.
Recoil impulse, 0.85 lbs.sec
Recoil velocity, 27.35 fps
Recoil energy, 11.62 ft.lbf
Even if my powder mass estimates are very far off, it doesn't change the result of the lighter bullet producing more recoil impulse, velocity, and energy.
Since the heavier bullet produced very slightly more penetration and expansion, it's fair to say that the performance was at least equivalent in a practical sense and we can't easily conclude that it might not have been quite as good as it appears.
It's interesting to note that it achieved these functionally equivalent results with considerably less muzzle energy, and even slightly less power factor.
125 gr, 565 ft.lbs muzzle energy
140 gr, 426 ft.lbs muzzle energy
125 gr, 178.25 power factor
140 gr, 163.94 power factor
While calculations suggest using the lighter bullet to achieve an equivalent muzzle energy will result in less recoil effect, they also show a heavier bullet will result in less recoil for a given power factor. Actual testing shows the heavier bullet achieving near equivalent penetration and expansion using lower muzzle energy, lower power factor, and with lower recoil effect. Fascinating.
My explanation? I suspect the lighter bullet is expanding more rapidly. Essentially, it's popping the chute earlier.
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