Aluminum bb's

[ThunderCactus]

Okay so your comparing a .28g cotton bb against a .28g granite bb, well thats great but we're not talking about rocks and cotton we're talking about aluminum and hard plastic, and believe it or not aluminum is actually VERY soft.
So what do you think does more deforming upon impact? The bb? or your skin/shirt/vest/face?
If an aluminum BB hits your gun, its not going to break or crack anything unless its a chinacrap or TM gun. And I've even seen plastic BBs crack plastic bodies. I say someone should conduct an experiment to measure impact force over time and penetration.
And I've heard some manufacturers make aluminum coated BBs, but for the most part we're talking about pure aluminum BBs.

[Flatlander]

Materials definately have an affect on impact and damage done (assuming constant size, mass and velocity). Think about hitting someone with a marble, then hitting someone with a bouncy ball - which will hurt more? Or if you've seen the mythbusters episode of the chicken cannon - frozen chickens have more penetration than thawed even though they have the same kinetic energy.

Aluminum generally has a higher yield strength than most plastics. A materials hardness is relative to it's yield strength so in theory an aluminum BB should pack more of a punch. However, with the velocities/impact energies we're dealing with may not be enough to actually feel the difference. Only way to test this is to shoot people with both...I'll volenteer to do some shooting in the name of science

[CDN_Stalker]

Originally Posted by ThunderCactus

Honestly I don't think it really matters. Is your skin hard enough to break a bb? No, infact I find it hard to believe a bb would deform at all upon hitting something as soft as skin.

Well, there IS a guy in the Ottawa area that claims a stock G36 shot a 0.20g BB fast enough that when it hit him in the hand it EXPLODED off his hand while playing in the CQB house.............. to which the user was immediately dragged off to the chrony by the victim and found it shot 280fps, 20fps under the CQB house maximum. Ever see a hot balloon deflate?

Originally Posted by DSFD506

I was told by a gun doc that the aluminum bb's are just plastic bb's with a metal coating. This true or not ?

Aluminum BB are made of soft aluminum. What the guy you refer to is talking aboiut is the Straight/Digicon BBs that are made of plastic but have a graphite coating on them. Shitty for guns with hop up, designed for non-hop up guns shooting very high velocities in competition matches in Japan against steel targets.

[FOX_111]

Originally Posted by CDN_Stalker

Ya, CO2 is expensive and it makes David Suzuki cry (fuck Al Gore, the more CO2 you use in your guns, the more he can justify the billions he's made from his Sci-Fi movie, and his new Nobel Peace Prize.............. those are currently available in Kinder Eggs, get yours while they are still available!!!)

Carbone monoxide and carbone dioxide is not the same thing. One of them is poluting, the other is not.

[CDN_Stalker]

Actually, both are dangerous in closed environments, but neither are "earth destorying".

I made a joke Fox, chill!

[FOX_111]

I know. It's the green hippy in me that is crying out hehe.

Seriously, I don't care that much, I just like to complain and morale people.

[ThunderCactus]

I'm not saying the aluminum BB WONT have more penetrating power, I'm just saying its not going to be significantly higher. As in it's not going to be breaking everyones goggles and tearing through BDU's.
As they are the exact same weight, the only place an aluminum BB is going to make a difference in performance is in a situation where a plastic BB would normally deform. So if a plastic BB doesn't deform when it hits your skin, why would an aluminum BB do more damage? It's not denser, or sharper, infact it's smoother on the outside so it may do LESS damage to your skin.
Now when shooting things like popcans, guns and goggles, BBs would normally deform in shape or explode to defuse impact force, so an aluminum BB would have much different results because it wouldn't deform nearly as easily.
So does anyone want to do a test? As much as I like science I don't want to get shot 20 times with different ammo just to get some hard results lol

[Nik12]

Originally Posted by MestHead

Materiel should matter, think about some one swinging a bag full of 1 pound of cotton and hitting u with it vs a bag full of 1 pound of rocks with the same force.

This kinda goes back to the 1kg at 1000m/s and 1 tonne at 1 m/s example. Which hurts more? Which does more damage?

Originally Posted by ryan_kristy

its diffrent they ocupy different space if you condensed the one pound of cotton into the same size as the rocks it wouldnt feel any different

Yes, it would. You are forgetting about a small little thing known as density. The density of the cotton, even if occupying the same volume as the rocks, would still be very small, making it still much softer and less hurt worthy.

Originally Posted by ThunderCactus

I say someone should conduct an experiment to measure impact force over time and penetration.

I concur. I'd volunteer to be a shootee, but I'm nowhere near any of this action.

Originally Posted by Flatlander

Materials definately have an affect on impact and damage done (assuming constant size, mass and velocity).

Constant mass and constant size (ie volume) would mean the density is constant for both test specimens. Which actually isn't unreasonable. Think about it, a .28g Aluminum BB and a .28g Plastic BB will have equal densities since they are both spheres with 6mm diameters. Mass and volume is constant for both specimens, so the density must be constant for both specimens, hence our assumption is justified.

Originally Posted by Flatlander

Think about hitting someone with a marble, then hitting someone with a bouncy ball - which will hurt more?

They would hurt about equally. Both would hurt alot. In order to maintain our assumption of constant density we need to think of the rubber ball as being hard rubber, much like a hockey puck. If I throw a marble at you then a ball made of hockey puck rubber both are going to hurt alot. The only difference will be the material properties (elasticity, yield strength, ultimate/fracture strength, etc), which can mitigate a small amount of hurt. Basically since the rubber will undergo a small amount of deformation (very small since it's hockey puck rubber), part of the impact energy (which contributes to hurtness) will be used to deform the rubber.

Originally Posted by Flatlander

Aluminum generally has a higher yield strength than most plastics. A materials hardness is relative to it's yield strength so in theory an aluminum BB should pack more of a punch.

I wouldn't believe the aluminum has a higher yield strength than most plastics, atleast most bb plastics. What happens when a stress is incurred in a metal that exceeds it's yield strength?
It deforms plastically, in other words once the aluminum (Al) has reached its yield strength and has either stretched or compressed the yield amount (yield deformation), any further elongation or compression will not be recovered when the applied load/stress is removed from it. Since we all know how easy it is to permenantly deform Al this means it has a relatively low yield strength.
Now think of the plastic. Plastic generally doesn't deform plastically (ironic, no?). Well atleast hard plastic doesn't deform in the same manner of plastic deformation that the aluminum experiences. A hard plastic specimen subject to small deformations across it's body will have several little plastic deformations (like biting/chewing on a BB will make little teeth marks). But if the whole body of the specimen is subjected to a load, then it acts more like a ceramic in which it's loaded until it experiences a fracture, no real plastic deformation. Due to this, the yield strength of the plastic is approximately around the ultimate/fracture strength of the plastic, ie yield is basically fracture.
As for a material's hardness being related to it's yield strength, this is not true at all. There is no correlation between hardness and yield strength. Hardness is more closely related to Toughness (which is the area under the stress-strain curve BTW), and toughness relates well to the amount of energy required to reach yield point and then the amount of energy required to permenantly deform a specimen x amount. This kind of brings us full circle, right now I just said that yield strength and hardness are related through energy, in a manner of speaking. So if we go back to your chicken canon, we have already agreed they have equal energies and equal densities, so this leaves us with the only variable being the deformation energies (elastic and plastic).
Now I could have just stated that from the beginning, but proving things makes it easy for everyone to see where your reasoning comes from (which isn't useful unless everyone understood the proof....).
Based on this reasoning, we know the Al BB will deform more than the Plastic BB since it's yield stress is lower, thus a certain amount of the impact energy will be used up inorder to perform the permenant deformation of the Al BB. This is the point where you consider strain/work hardening, but over such a small sample that the BB is it's affect is negligable. Based on all this, I'd conclude that the Al BB would theoretically hurt less than the Plastic BB. However as stated below by Flatlander:

"with the velocities/impact energies we're dealing with may not be enough to actually feel the difference"

This is true, since the BBs already only impart a small amount of impact energy the affect of the deformation is essentially negligable aswell, and it would be a fair conclusion to say that they will basically feel the same (same amount of hurt).

The reason why the hurt difference occurs in paint ball when a ball either breaks or doesn't is because paintballs impart alot more impact energy then our BBs do, so the deformation affect is greatly emphasized.


Just my $2x10^-2

[ThunderCactus]

So to sum everything up, what we've learned by discussion is:
1) An aluminum BB is likely to do more damage against hard objects that would normally deform or break a plastic BB.
2) An aluminum BB is likely to cause the same effect as a plastic bb upon contact with skin due to the same density, weight, and size.
3) The BB's don't normally travel at a high enough velocity that you could really make a performance difference.
4) Plastic BB's break teeth too, so why worry about aluminum?

So what we need to test is:
1) Effect of plastic vs aluminum BBs on skin.
2) Effect of plastic vs aluminum BBs on gear, goggles and plastic guns.

[Flatlander]

Originally Posted by ThunderCactus

I'm not saying the aluminum BB WONT have more penetrating power, I'm just saying its not going to be significantly higher. As in it's not going to be breaking everyones goggles and tearing through BDU's.
As they are the exact same weight, the only place an aluminum BB is going to make a difference in performance is in a situation where a plastic BB would normally deform. So if a plastic BB doesn't deform when it hits your skin, why would an aluminum BB do more damage? It's not denser, or sharper, infact it's smoother on the outside so it may do LESS damage to your skin.
Now when shooting things like popcans, guns and goggles, BBs would normally deform in shape or explode to defuse impact force, so an aluminum BB would have much different results because it wouldn't deform nearly as easily.
So does anyone want to do a test? As much as I like science I don't want to get shot 20 times with different ammo just to get some hard results lol

I agree with you. I don't think that there will be a noticable difference in pain or damage sustained to the person. If I do recall correctly, the ANSI safety rating for eyewear is performed with a steel projectile so eyewear should be fine.

Now ABS plastic has a yeild strength of around 30 MPa and annealed aluminum (softest you'll find I believe) is around 15-20 MPa. Low grade engineering aluminum is around 90 MPa. So there's a good chance that the aluminum BB's are stronger than the plastic ones.

I think it was Madmax who did the impact energy testing on mechboxes and found that the aluminum piston heads are killer on V2's (as is the consensus reading into the topic with people using aluminum heads on V2's). This is because the plastic piston heads will absorb (or NOT transfer) the energy as well.

[Flatlander]

Nik:

If I recall correctly from my engineering materials class I took last year, hardness is directly related to yield strength (or ultimate strength in brittle materials as ultimate and yeild are about the same as you mentioned). I recall the equation to find the hardness (I believe it was rockwell) of a material was a constant multiplied by the yeild strength.

Note that hardness (engineering hardness) is found by measuring the PERMANENT deformation in a body after a load is applied to it. So, the toughness of the material (AKA energy able to be absorbed) has nothing to do with the hardness.

**EDIT**

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

Vickers harness test (similar to rockwell) - There is an equation relating the hardness to the yield stress.

[Flatlander]

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

Note the Stress-Strain curves for steels and brittle materials and you will understand the following.

Originally Posted by Nik12

As for a material's hardness being related to it's yield strength, this is not true at all. There is no correlation between hardness and yield strength. Hardness is more closely related to Toughness (which is the area under the stress-strain curve BTW), and toughness relates well to the amount of energy required to reach yield point and then the amount of energy required to permenantly deform a specimen x amount.

Consider ceramics (brittle materials with high yield/ultimate strengths) and regular structural steels (lower yeild strengths). Now when you look at toughness you look at the area under the curve as you said - this includes ALL the area including the plastic deformation until failure occurs. Now ceramics are much HARDER than steels but have far less toughness (or area under the curves). So (some)ceramics have higher yeild strengths, harder, but less area under the curve than steels. This is why you use ceramics as wear surfaces (ie), because they're hard. We use steels in structures and things because they are tough and will show signs of failure before it occurs.

**EDIT**

Ah ha, I found that little bastard of an equation:

tensile strength (MPA) = 3.45 * HB where HB is the Rockwell hardness rating and noting that only approximate yield strengths can be determined from the hardness of a material.

[Nik12]

Originally Posted by Flatlander

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

Note the Stress-Strain curves for steels and brittle materials and you will understand the following.



Consider ceramics (brittle materials with high yield/ultimate strengths) and regular structural steels (lower yeild strengths). Now when you look at toughness you look at the area under the curve as you said - this includes ALL the area including the plastic deformation until failure occurs. Now ceramics are much HARDER than steels but have far less toughness (or area under the curves). So (some)ceramics have higher yeild strengths, harder, but less area under the curve than steels. This is why you use ceramics as wear surfaces (ie), because they're hard. We use steels in structures and things because they are tough and will show signs of failure before it occurs.

No need to tell me that, I am majoring in Civil Engineering. But you are right. That's my bad. DOn't know whta I was thinking. However, if we think of Al as having a lower yield strength, then it's hardness is also less. Which still implies the Al BB shouldn't impart any extra impact energy than the Plastic BB.

Originally Posted by Flatlander

Nik:
If I recall correctly from my engineering materials class I took last year.

Just finished one this past semester (and a very basic one in First year). Although a large part of it was based around Concrete, Structural Steel, Wood and Fibre Reinforced Polymers (ie using Carbon Fibre/Fibre Glass/Kevlar to reinforce Concrete instead of Steel). Only a mediocre unit on properties of materials.

Originally Posted by Flatlander

Note that hardness (engineering hardness) is found by measuring the PERMANENT deformation in a body after a load is applied to it. So, the toughness of the material (AKA energy able to be absorbed) has nothing to do with the hardness.

That is true, my bad. Although you can't say toughness has nothing to do with it, it takes a certain amount of energy to permenantly deform the sample. I'm sure an empirical equation relating the two could be derived.

[Flatlander]

Nik:

We've all had those brain farts. Fortunately for me, mine usually occur during exams They try to ram all that information into your head - you push something in and force something out at the same time it seems!

As for the yield strengths of the materials (as mentioned before):

ABS plastic - around 30 MPa
Annealed Al - 15-20 MPa
Low grade Al - 90 Mpa

So, no way to tell which is stronger unless we get the exact composition of the materials or someone tests them.

[Hades]

I used those metal bb's from ArmyIssue in my APS/2 which is chronied at 500+fps with .20's and they did not have enough force to penetrate 1 side of a plastic water bottle, just dent it a little