I guess because the number is an average number calculated considering all the penetration distance travelled by the bullet.
..it depends on bullet shape and bullet behaviour during the gel/tissue penetration...
...if the bullet during its travel inside the gel or soft tissues penetrates point first with minimal angle of attack the TC shape is a bit better from a tissue crushed point of view...
I write "a bit" because meplat sizes and rounded edges of the usual TC bullets can be good for weapons reliability but not so good to have high minimal Cds...
...the problem here is that during the travel the angle of attack can be not minimal nor constant during the entire penetration distance...and the Cd of the bullet depends even on it....much like what happens for aircraft wings...
...for example in the case of 9mm bullets...if the distance of penetration in gel or tissues is quite short(..10 or 15cm) with similar bullet masses and impact velocities the energy spent by TC can be a bit larger than the energy spent by RNs...so the Cd in cavitation regime of the former is a bit larger...so it crushed a bit more tissue...
...but if the soft target is thicker it can happen the opposite for the reason written above.
...it's the reason why the Cdc suggested by Mr. Duncan McPherson to calculate the penetration distance in soft tissues by pointed rifle bullets that eventually don't tumble in the media is higher than the minimal Cdc such bullets have because their shape only....
...and it's the reason why for 9mm and 45 FMJRN bullets using the data written by 200RNL in the previous post if you consider the thickness, type and strenght of the gel blocks used by the Southwestern Institute of Forensic Sciences of Dallas, the calculated Cdcs range from 0.21 to 0.23, so near the minimal value for such shapes...
...it means too that for the penetration distance considered while the energy lost by 9mm and 45Auto FMJRN's is about the same the tissue crushed by the latter is much larger mostly because its larger
presentation area...
...some pics I took months ago...the media was animal gel...the first two are about the holes left by 9mm FMJRN(..manufactured by Sellier & Bellot) and a .22" 40 LRN(manufactured by Fiocchi) bullets after 5cm penetration...the other two pics are about the holes left by the 9mm bullet after 15 cm penetration and by the .22" cal. bullet after 25cm penetration...obviously for the same bullet the angle of attack was not the same at the penetration distance considered...the impact velocities were about 1055 fps for the 9mm and about 1100 fps for the .22"...
All the best
Andrea
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