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Yup.
Speed is the name of the game when it comes to steel penetration, unless you step up to a large, heavy penetrator as found in M995. The "penetrator" in M855 is laughable, and really only serves to provide a bit more extra spall to deal with when shooting at steel.
1/2" steel is fine, but heavier than needed and produces even less movement and ring than 3/8".
And all this time I've been avoiding M855... I assume the M193 has higher velocity because of the lighter weight? Obviously I'm not well-read in most ballistics yet. And does the 1/2" have any benefits that make it worth while? Better longevity or more durability at closer range, etc?
The biggest difference that I have seen in steel targets is in manufacturer quality. I trust companies like MGM, Tac-Strike, and Porta-Target, having seen tens if not hundreds of thousands of rounds pushed into them at responsible distances of several calibers. I do not trust random steel distributors' offerings.
Frankly, I have not seen sufficient quantities of 1/2" steel in direct comparison to 1/4" or 3/8" to offer any insight beyond that already given. Once again, longevity is not based on perforation, but rather deformation of the front face, and once the front face is severely pitted the target should be moved to long(ish) range (100 meters or greater), and shot until it crumbles.
It's a physics thing, and your assumptions are correct in this particular case.
Kinetic energy at point of impact is the key.
Both rounds fired on a level line will hit the ground at the same time, M855 significantly farther out, even though M193 got to the 1/3 mark significantly sooner. Velocity & weight factored together equals the amount of force transmitted to the target.
A properly worded search phrase will turn up more than you wanted to know about the subject on these two particular rounds.
3/8" AR is probably the better plan for weight and cost. If I can get a slight dome to the face, it should increase the longevity. Maybe even a little hammer treatment.
Sticks
Grasseater // Grass~eat~er noun, often attributive \ˈgras-ē-tər\
A person who is incapable of independent thought; a person who is herd animal-like in behavior; one who cannot distinguish between right and wrong; a foolish person.
See also Sheep
I keep hearing this about PMC. I've consistently chronographed Bronze 55grain consistently at 2880 FPS from my 16 inch Noveske. How are we defining "mild"?
Here's a magazine of 55 gr PMC Bronze out of my 11.5 SBR (2450 FPS) from about 35 yards on a 1/2 inch AR500 gong.
http://m.youtube.com/watch?v=vtpGrPpxIEA
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