The diameter of the permanent cavity decreases with penetration. This is because soft tissues will stretch around the contours of a penetrating bullet, and as the bullet slows down more tissue stretches around the bullet rather than being crushed.
Bullet shape is also another important factor. A wadcutter bullet, with its sharp shoulder, crushes a much greater percentage of tissue in relation to its diameter, than bullets whose shapes are round nose, flat nose, or expanded JHP.
An unexpanded .22 LR bullet doesn't crush a permanent cavity that's 0.22 inches in diameter. It's more like 0.15 inches average diameter, which means that during the last few inches of the wound track, where the bullet's velocity has slowed considerably and more tissue is stretching around the bullet than being crushed, the diameter of the permanent cavity is even smaller. So if you manage to hit a vital circulatory system structure the hole is not going to be very big. The hole produced by a .22 Quik-Shok fragment will be even smaller. While hitting vitals is the whole idea, the hit(s) you obtain have to produce enough damage to facilitate rapid blood loss. A vital hit by an unexpanded .22 HP is going to produce a more efficient wound than a vital hit by a Quik-Shok fragment.
6-inches of penetration isn't enough to ensure the bullet will not only reach vital blood distribution organs, but pass through them as well. And this is when penetration conditions are most favorable. An arm in the path of the bullet or an unusual penetration angle that requires deeper penetration to reach vitals than the bullet is capable of achieving is a recipe for disaster.
Does Quik-Shok actually increase the odds of hitting something vital? There's the possibility that your well placed shot, in which your bullet is on track to pass through a major vessel, could be defeated because the fragments veer off at an angle and miss the vessel completely. The idea is to make each shot count. You may fire six times but only get one hit, or get only one good hit. It would be a shame if that one good hit was ineffective because the bullet didn't penetrate deeply enough or it was inefficient in destroying tissue.
Additionally, one of the bullets you fire into a bad guy's sternum might be on track to sever or severely damage his spinal cord and instantly eliminate or substantially reduce his ability to remain a danger to you. Quik-Shok doesn't give you this combat capability.
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/s/ Shawn Dodson
Firearms Tactical Institute
http://www.firearmstactical.com