Letter Re: Securing Windows With Plywood The Fast And Easy Way

Dear Jim:
To follow up on the recent letters, we supply roughly half inch thick ballistic steel to stop .30-06 AP threats. (NIJ  Level IV ).

The tradeoff is that you are looking at roughly double the weight — 20 lbs. per square foot.  So for the hypothetical 36″ by 36″ piece it adds up to roughly 180 lbs.  Ceramic tile can provide AP or Level IV protection at less than half that weight – but much more expensive.

Your point about spall is well taken. I would worry most about the bullet splatter or ricochet from a round plastering itself onto the threat side face of steel plate.   Eye protection is mandatory anytime firearms are in use, but especially here.

Your idea to angle the plate is a great one. Just be sure you are directing ricochets and bullet splatter in a safe direction!   (You do not want to have your head sticking up over a plate angled toward you!)   Ideally, you want to direct bullet splatter and ricochet away from you.  So shutters that lock open at an angle are an idea here, to give a protected firing port.

Assuming a bullet that would otherwise be a perfect 90 degree hit, a .25″ thick steel plate angled at 45 degrees effectively gives you a 0.35″ plate thickness. Or in metric terms, 6.4mm becomes almost 9mm.  Over 40% more effective thickness, plus you are encouraging the round to take the path of least resistance, and ricochet rather than penetrate.  There is a good reason that tanks have sloped armor on the front!
Yours truly, – Nick at BulletProofME.com Body Armor