Funny thing about the angle of incidence equaling the angle of departure/refraction - at least, in Iowa, that formula doesn't work!

I believed in that, until I received my 4'x 8'x 1/2" 550AR plate from
Field & Cave (thank you, Travis & Co.), got a frame built, and began shooting at it . . . it turns out that
mass and momentum TRUMPs the angle of departure/refraction . . .
and NOT by just a little bit!


I have attached (i hope) some pics - yep, I was dismayed!!
Not a single bullet (not even 22 rim-fire stuff) glanced off at the reciprocal 45 Deg. angle, thus straight down into the "trap"!

T
he bullets impact the plate, leave a small mark of some sort, "slide" right along the face of the plate, and impact the ground, cutting a narrow "rut" behind the plates lower edge.
Due to some health issues, and shooting mostly rim-fires, to keep neighbor sane, the grass is a little taller that it should be.
Regarding penetration on steel vs animal tissue - never confuse these: there are two completely different processes taking place!P.O. Ackley demonstrated this nicely - way back when!
When relying on a steel plate bullet stop, small diameter, and velocity make for bad JuJu - again, see the pics. The fairly deep pock-marks - about 1/3 the depth of the plate - were the result of 20 Cal., 40gr bullets at MV of 4040fps. The large 'yellowish' stains are paint - the smaller "whitish" stains are the leavings of 160gr bullets, which departed the 7mm DAKOTA muzzle at about 3250fps, and 88 &110gr bullets which,respectively,exited the .257/300WSM @ 3950 & 3540fps - not even a "ding".
No more 20BR shooting - especially "groups"! I thought/believed that the AR550, at 45 Deg. would prove immune to even the 20 Cal. - wrong again. Oh, the .204 Ruger, same 40gr bullet, at about 3800fps roughs it up some, while the VarTarg (probably about 3300fps) is pretty forgiving.

RG
P.S. Not clear in pic, but like farmerjohn's, it's on a sled, for relatively easy re-location: the plate angle is adjustable, and also lays "flat" - low CG - for transport in trailer.
P.S. again: After some thought, the only time the angle of departure would equal the angle of incidence, would be if the bullet impacted surface at an obtuse angle, as opposed to our acute angle set-ups.
