How many blades a point has changes penetration differently depending on the target

The summary today

A single ballistic experiment, well run but with crossbow bolts and modern hunting points, says the answer depends on the target. At the same impact energy, between 18.5 and 18.9 J with no significant differences, in a clay block penetration falls by 6.2% with three blades and by 12.5% with four compared with a two-blade point; through thick leather the sign reverses. Through one 3 mm layer the two-blade point stops in five shots out of ten, between 188 and 270 mm, while the three- and four-blade points always travel the full 300 mm available; through two layers penetration rises by 14% with three blades and by 25% with four, but with two or three shots per configuration and no statistical test. The advantage does not come from easier cutting: the leather's resistance does not change with the number of blades through one layer and rises through two, while friction on the shaft behind the point falls by 43% with three blades and by 56% with four, because the hole is wider. It is a single paper, written for the archaeology of Iron Age arrowheads, and in the three-blade configuration the blades were not at 120 degrees, which made the bolt flex by about 2 mm; nobody has yet tested targets that resemble an animal.

Also phrased as: "two-blade or three-blade broadhead"; "broadhead penetration"; "how many blades should a broadhead have"; "trilobate and quadrilobate arrowheads"; "most effective hunting point"

Evidence

• 2023
  For Equipment tests Published later

  24 g crossbow bolts with removable-blade hunting points in 2-, 3- and 4-blade configurations, impact speed 35.2 ± 1.1 m/s. In clay, 10 shots per configuration: penetration -6.2% with 3 blades and -12.5% with 4 compared with 2 (ANOVA F(2,27) = 9.30, p = 0.0008). Through one layer of 3 mm leather the 2-blade point stops in 5 shots out of 10 after 188 to 270 mm, mean 263 ± 46.3 mm, while with 3 and 4 blades every shot travels the 300 mm available; through two layers +14% with 3 blades and +25% with 4 (66, 75 and 82 mm), with 3, 2 and 2 shots and no statistical test.

  Reassessing the terminal ballistic performance of trilobate and quadrilobate arrow points on Iron Age battlefields · Devin B. Pettigrew, William Taylor

• 2023
  Context Equipment tests Published later

  The mechanism: after one layer of leather, friction on the shaft falls from 48 ± 12.2 N with 2 blades to 27 ± 6.2 N with 3 (-43%) and 21 ± 4.5 N with 4 (-56%) (F(2,27) = 28.3, p < 0.0001), while the leather's resistance to the point does not change with blade number through one layer (235, 217 and 235 N; F(2,27) = 0.86, p = 0.44) and through two layers rises by 7.7% and 17.6% (623, 671 and 732 N, tiny samples). Most of the gain in shaft drag already comes with the third blade.

  Reassessing the terminal ballistic performance of trilobate and quadrilobate arrow points on Iron Age battlefields · Devin B. Pettigrew, William Taylor

• 2023
  Context Equipment tests Published later

  Adding or removing blades does not change kinetic energy or momentum: 18.5, 18.8 and 18.9 J (F(2,64) = 0.53, p = 0.59) and 1.05 to 1.07 kg m/s (p = 0.063), so the differences come from geometry. In the 3-blade configuration, with blades not set at 120 degrees, the bolt flexes and deviates by about 2 mm during penetration, measured on video at about 8,800 frames per second; the authors think this raised the initial forces.

  Reassessing the terminal ballistic performance of trilobate and quadrilobate arrow points on Iron Age battlefields · Devin B. Pettigrew, William Taylor

Status history

1. 2023 Reported The only controlled experiment comes out, with statistics and at equal impact energy (18.5 to 18.9 J, no significant differences): in clay penetration falls by 6.2% with three blades and by 12.5% with four, while through leather the sign reverses, with gains of 14 and 25%, and through a single layer the two-blade point stops in five shots out of ten where the three- and four-blade points always complete the run. The mechanism lies in friction on the shaft, which falls by 43% with three blades and by 56% with four, not in easier cutting. It is a direct test on equipment, but a single paper, using crossbow bolts: the supporting evidence is there and it is limited.

Other claims in this domain

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