memtb,
Unfortunately, retained weight doesn't have nearly as much effect on penetration as frontal area of a bullet....
It does seem that way sometimes,
but penetration tests done with 9,3x62 in elephant showed that weight retention was ones best friend by a large margin.
WL 286gn went 20"
WL 320gn went 40"
NP 286gn went 23"
AFrame 300gn went 42"
The 286NP is only 5% lighter that the AF300 and NP had rather noticeably smaller expanded dia. than the AF.
so the NP should be the winner, yes?...well no, since NP penetration was miles behind the AF.
Final weight for NP was 217gn (75%) and the AF 298.5gn.(99%)
Regarding the “winner”, initial and final weights and final expanded diameter only tell part of the story. How fast the bullet expands plays an important role. My guess is the NP expanded sooner/faster.
Impact velocity also plays an important role. Given identical bullets, it has been shown many times that the slower bullet will often penetrate deeper. This may be in part or even mostly due to how soon/fast the bullet the bullets expand or it may have to do with the mechanical properties of the impact – push your hand flat into water and there is no problem, slap it into the water fast enough and your hand will turn to mush.
For example, take a couple of .458” hardcast FN bullets fired from my .45-70 into water jugs. The first was a 460g Cast Performance WFNGC @ 1812fps while the second was a 300g Oregon Trail Laser-Cast bullet at 1167fps. The 460g bullet (461.2g actual) had a sectional density of .314 and started out with 3362 ft-lbs energy and a relative momentum of 836 while the 300g had a sectional density of .204 with a paltry 907 ft-lbs energy and a relative momentum of 350. After firing into the water jugs the 460g bullet retained 352.9g with a maximum width of 0.58” (due more to a bent/deformed tip leaning to one side than true expansion). Expansion and final weight of the 300g bullets was unknown as none were recovered but the Laser-Cast bullets are hard and little expansion or weight loss, if any, is likely.
Given just these numbers many people would expect the 460g bullet to penetrate further – after all it had 1.54x the mass and sectional density, 1.55x the velocity, 3.7x the energy and 2.4x the momentum, all packaged into a projectile with the same diameter and (more or less) construction. Those people would be wrong – way wrong.
In fact, the 460g bullet stopped in the 9th water jug. The 300g bullet repeatedly exited 12 water jugs. One notable difference was the amount of destruction. The 460g bullet violently destroyed many of the water jugs while the 300g passed through the 12 jugs destroying one or two but leaving only entrance and exit holes leaking water in the rest.
Another bullet tested was the 350g North Fork SS at 2189fps. This bullet started out with 3726 ft-lbs energy and a relative momentum of 767. It expanded to 0.80” and stopped in the 6th water jug. Not only did this bullet violently destroy most of the water jugs, it did a lot of damage to the sawhorses and plywood surface the jugs were resting on as well. The plywood was a 12” wide strip of 1/2” or 19/32” plywood. The front water jug was resting on the leading edge of the plywood, flush against the right side. The bullet impact not only destroyed a lot of the water jugs, the concussive force blew a hole in the plywood that matched the footprint of the first water jug. The force also broke the horizontal support of the front sawhorse, dropping the plywood and water jugs to the ground. It just goes to show that penetration is not a good measure of a bullet’s destructive ability. If it was we would all be shooting non-expanding spire point solids for big game hunting.
