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EXPANSION AND WEIGHT RETENTION

QUESTION
At what velocity will GS Custom FN Bullets start expanding?

The FN Solid Bullet range will expand if driven hard, and is almost impossible to break or bend. If your rifle is capable of the speed required to expand an FN bullet, performance will exeed that of the "paper ballistics". It is strongly advised that you forget about
sectional density and all the baggage we have all accumulated regarding the penetration of heavy bullets. Use the lighter FN bullets to get the speed up and take advantage of the FN technology.

Acknowledgement and thanks to Dan McCarthy for the picture below.

From left (all GS Custom):
(1) unfired 570 grain 500 Nitro Express bullet
(2) 570 grain 500 NE bullet fired into elephant (frontal brain) - penetrated 74 inches, but missed neck vertebrae
(3) 570 grain 500 NE bullet fired into elephant (frontal brain) - penetrated 31 inches and stuck in neck vertebrae
(4) 570 grain bullet fired into buffalo (body shot) - penetrated 60 inches
(5) unfired 500 grain .470 Capstick bullet
(6) 500 grain .474" bullet fired into buffalo (body shot) - penetrated 56"
(7) 500 grain .474" bullet fired into giraffe (body shot) - penetrated 40"

 

From Left to right:

500gr .470 from Elephant, 540gr .510 from elephant, unfired .510, 450gr .458 from stop box at 2450fps, 450gr .458 from stop box at 2000fps, 450gr .458 unfired

Proving the virtually indestructible nature of FN bullets, these bullets were fired into a steel drum filled with sand. From left to right:

270gr from a 378 Weatherby, 270gr from a 375H&H, 270gr .375 unfired, 450gr at 2700fps from a 460 Weatherby, 450gr at 2300fps from a 460 Weatherby, 450gr .458 unfired.

 

QUESTION:
I shot two whitetail deer at approx. 160 and 215 yards. Both dropped like stone. Neither shots were spined but both dropped like they were. Both shots were high, being near the apex of the trajectory, but the closest was about 2.5 inches from the spine.  Have you heard of this before with your bullets? Do you think the velocity could cause hydraulic spine damage?

ANSWER:
What you have experienced is classic HV performance. When we started down the road with the HV design, we noticed that the faster we drive the bullets, the more dramatic and the more frequent were the incidents of one shot knockdowns. With no bullets recovered from game in the initial testing phases, we assumed that the bullets mushroomed and had extremely high weight retention, as that was what our HP range was doing. We also noticed that the softer (easier to expand) we made the HVs, the better they worked at all distances on game. All along we were puzzled by the fact that exit holes appeared to be only slightly bigger than calibre size. Close shots produced bigger exit holes but meat damage was still less than what we expected, given the speeds we were getting.
 
Then, in fairly quick succession, we were confronted by some very strange facts. We recovered a number of small calibre bullets from large animals where the bullets worked extraordinarily well. All of them were the same shape. The petals were completely torn off and the bullet front was expanded to a virtually flat shape. Weight retention was around 80 to 85 %. Experimentally, we then designed some hard bullets and some soft bullets and went shooting animals. 

In every instance where we had double calibre or more expansion with full weight retention, the effect on the animal was less dramatic than with the "soft" bullets that broke down to 80% or so. To add to the confusion, our FN bullets were becoming an unprecedented success. Wound channels from the FN bullets resembled those of soft nosed premium bullets that expand to double calibre and more. 

Clearly something was better about the soft HV design and the FN flat nose. For someone like me with forty years worth of input that said "good mushroom, maximum weight retention" it was impossible to figure out.  The results were indisputable though, and the HV concept was born. While we designed HV bullets that would go as fast as possible, completely expand in one to two inches, throw off the three petals and then carry on as an expanded cylindrical shape, we searched for an answer to explain why the effect was so dramatic.
 
The explanation came in the form of an excellent book by Duncan MacPherson - "Bullet Penetration". His research reveals a couple of things. 1. It removes all doubt that the most valuable wound trauma incapacitation mechanism is a single large wound channel. 2. It proves conclusively that the most reliable instrument with which to inflict the maximum amount of disruption was a vertical faced, sharp edged projectile.
 
The reason why a cylinder shape is so much better than all other is because of the manner in which it displaces the tissue it encounters. 

A rounded shape of any description displaces tissue to the sides of the wound channel in the time it takes for the front of the shape to move forwards and be replaced by the full width of the shape, creating a primary wound channel. Although this happens very, very fast, a rounded shape therefore contains a time and distance element that translates to a level of force imparted to the tissue. This makes the tissue continue to stretch away from the bullet path, creating a temporary wound channel, until the elasticity of the tissue overcomes the force and brings it back to the original position. Some of the tissue would have been disrupted and this would add to the total size of the primary wound channel. 

A cylinder shape encountering tissue, displaces the tissue to the side vastly faster on a time/distance basis than any other shape. This imparts a far higher force to the tissue, pushing it much further from the primary wound channel, disrupting more tissue beyond the limits of elasticity and ultimately contributing to a much bigger primary wound channel.
 
Now there was clarity about the FN bullets as well. The HV design was in fact only an HV in flight. A couple of inches after impact, it would resemble an FN bullet.
 
In practise we see with HV and FN bullets that soft aqueous tissue such as the lungs, liver, brain, large blood vessels and stomach contents suffer massive trauma with HV and FN bullets. Firmer tissue such as meat, heart and kidneys survive much better.
 
Another point MacPherson mentioned in his findings was that, when the larger temporary cavity included a vital element, such as the liver (or spine in the case of your two shots), the damage to those elements was enough to cause disruption and incapacitation.
 
The bottom line is that traditional bullets, that depend on a mushroom, may or may not work. In some instances they break up too much and fail to penetrate deep enough, and sometimes the forces are not high enough and they do not expand at all. With HV bullets the worst that can happen is a good mushroom, if speed falls to really low levels. At speeds over about 2600 fps, the petals part company and it turns into a totally reliable mechanism that works in the same manner with monotonous regularity.


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GS Custom Bullets, situated in Port Elizabeth on the East Coast of South Africa, manufactures solid copper, turned, monolithic bullets for hunting and sport shooting. These bullets are used by hunters on several continents, hunting from the smallest of antelope to the largest of dangerous game, using the smooth HP bullet, as well as the more popular HV, FN and SP bullets with the patented drive band concept. GSC bullets are configured for the highest possible ballistic coefficients. SP bullets are mainly used for sport shooting. All GS Custom Bullets are moly coated.