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Thread: Optimim Angle for Armor Plate

  1. #1
    Senior Member kyratshooter's Avatar
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    Default Optimim Angle for Armor Plate

    I really hate to divert thought from such important matters as shooting astronauts into orbit riding .22LR shells and the quest for accuracy from plastic pistols but I have a question for some of the balistics gurus here.

    A thorough search of the internet reveals that everyone has an opinion but no one has any facts to solve my problem.

    I have acquired a section of 1/4" steel plate which will be used as the bullet stop for the back yard range. Yes, pistol bullets only and cast bullets exclusively.

    What is my optimim angle to maximize metal strength, and insure the lead will divert into the catch area at the bottom of the trap?

    I do not want bullets comming back foreward of the base or escaping out the bottom rear of the trap.

    Simple common sense math says a 45% angle would be proper, but is it the best angle scientifically?

    "Just buy one" is the wrong answer! It is the most popular answer on a google search, but not the right answer.
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    Administrator Rick's Avatar
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    KY - You are looking for the Rolled Homogeneous Armor equivalency and the slope is 60°. That slope will double the thickness of your steel.

    http://en.wikipedia.org/wiki/Sloped_armour

    "For example, armour sloped sixty degrees back from the vertical presents to a projectile travelling horizontally a line-of-sight thickness twice the armour's normal thickness..."
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    Lone Wolf COWBOYSURVIVAL's Avatar
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    I am not a ballistics expert by far. But I am pretty good at 8 ball and work with steel on a daily basis. .250" plate could be alot of things. If it is truly fractional steel it will be a full .250" thick, if it is gauge steel it could be a little thinner, most likely .229" thick. Not that it is a big difference, just passing on what I know. Another consideration is the steel designation. If it is mild steel like say 1010 modified it will have a low yield strength but high tensile strength (most likely deform but not fail) Most higher carbon steels will be sold in an annealed state in sheets which will have a higher yield strength but lower tensil strength, (it may split or crack rather than deform. Most likely it is the lower carbon variety. I'd set the angle at 33.3 deg. and drop the trap base further back. Just my 2 cents. I have seen FMJ's go through .375" mild steel @ 90 deg.
    Keep in mind the problem may be extremely complicated, though the "Fix" is often simple...

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    Lone Wolf COWBOYSURVIVAL's Avatar
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    Quote Originally Posted by Rick View Post
    KY - You are looking for the Rolled Homogeneous Armor equivalency and the slope is 60°. That slope will double the thickness of your steel.

    http://en.wikipedia.org/wiki/Sloped_armour

    "For example, armour sloped sixty degrees back from the vertical presents to a projectile travelling horizontally a line-of-sight thickness twice the armour's normal thickness..."
    Me and Rick posted at the same time in effect saying the same thing, Good show Rick!
    Keep in mind the problem may be extremely complicated, though the "Fix" is often simple...

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    Senior Member kyratshooter's Avatar
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    This is measuring a full .250" and the only designation at the supply house was "mild steel".

    Again, this is going to be .22 rimfire for the most part with the occasional cast bullet centerfire pistol load. I load my 9mm at about 121gn/950 fps and my .38 spl is loaded to about 150gn/850 fps.

    No centerfire rifle or high velocity pistol and no FMJ at all. The shooting club is only 2 miles down the road and they have better rifle facilities than my little acre will provide.

    I am just wanting to be able to walk out the back door and plink with the .22 and not have to wait a turn at the range or wait for a ceasefire to change targets.

    The way I have it figured I have a 50 yard downhill shot from the back porch, past the 3d archery targets to the new backstop.

    I just wanted to insure maximum efficiency for something as simple as setting the angle of the plate. That and I am so stingy I want to recycle the lead as it accumilates in the trap.
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    Lone Wolf COWBOYSURVIVAL's Avatar
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    Quote Originally Posted by kyratshooter View Post
    This is measuring a full .250" and the only designation at the supply house was "mild steel".

    Again, this is going to be .22 rimfire for the most part with the occasional cast bullet centerfire pistol load. I load my 9mm at about 121gn/950 fps and my .38 spl is loaded to about 150gn/850 fps.

    No centerfire rifle or high velocity pistol and no FMJ at all. The shooting club is only 2 miles down the road and they have better rifle facilities than my little acre will provide.

    I am just wanting to be able to walk out the back door and plink with the .22 and not have to wait a turn at the range or wait for a ceasefire to change targets.

    The way I have it figured I have a 50 yard downhill shot from the back porch, past the 3d archery targets to the new backstop.

    I just wanted to insure maximum efficiency for something as simple as setting the angle of the plate. That and I am so stingy I want to recycle the lead as it accumilates in the trap.
    Ok then I would go with 45 deg. if all your using iss .22 you'll have an easier time collecting them straight down. >22 will never damage the .250 mild steel at that angle.
    Keep in mind the problem may be extremely complicated, though the "Fix" is often simple...

    "Teaching a child to fish is the "original" introduction to all that is wild." CS

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    Lone Wolf COWBOYSURVIVAL's Avatar
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    Another option...I use a 55 gallon plastic barrel filled with sand. There are hundreds of .22 rounds sitting in the barrel.
    Keep in mind the problem may be extremely complicated, though the "Fix" is often simple...

    "Teaching a child to fish is the "original" introduction to all that is wild." CS

    "How can you tell a story that has no end?" Doc Carlson

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    Administrator Rick's Avatar
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    I don't think you'll have too much of a problem with any angle between 33 and 60. The Russian's discovered the RHA equivalency and incorporated it into their T-34 tanks. Their frontal armor was 15mm set at 30 degrees and netted them an RHA of 51mm. The Germans quickly adopted a similar strategy and by using an angle of 31 degrees their 50mm frontal armor on the Panzer IV had an RHA of 52mm. I do know the T-34 was tested at Kubinka by firing four rounds of British 37mm AT at them with no effect. So your .22 should be pretty easy to contain. Try some angles and see what works for you.
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    Senior Member kyratshooter's Avatar
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    I got to looking at my situation and built the rack with the plate at 45% just for the ease of construction. This gives me a 15" vertical opening 52" wide as the target opening.

    I now have the ability to adjust the impact angle by changing the angle of the entire unit as needed.

    I finished up just before dark. I will get a pic loaded up tomorrow. I made the rack from 2x4 with a "sandbox" on the bottom to catch the deflected slugs.

    It was too dark to shoot at it when I finished so I will try it out tomorrow.

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  10. #10
    Administrator Rick's Avatar
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    You know what? I forgot about that .22 around the world thingie. You might want to order more steel plate.
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