Shattering Glass with a gun?

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Geronimo45

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The History Channel's shootout mentioned some instance of a SWAT intervention... long story short, a SWAT sniper with what I think was a .308 took a shot at a BG inside a shop of some kind - the guy was less than fifty yards off, and the window shattered, didn't do a lot of damage to the guy on the other side. Now, that could be the deflecting due to hitting the glass (which is usually pretty thick on the stores I've seen), or a bad shot... or any number of factors.
My question was, if one wanted to shatter reasonably-thick glass with a gun, what would be the most important factor - velocity, bullet weight, bullet shape? What bullets would be more prone to shatter the glass than just punch a hole through it?
 
I don't know. What follows is pure conjecture.

My guess would be that a fairly slow bullet with an extremely wide meplat would be most effective at shattering glass rather than punching through it.

I'd say that a .45 Colt at 650 fps with a .335 meplat would work quite well. Personally I don't know and have no real way to test the theory.
 
Generally, I think that velocity is going to be the key factor as to whether the bullet punches a hole or shatters the glass. The higher the velocity, the less likely to shatter.

Of course it depends on the projectiles used (ie - FMJ, soft-nose, etc), how much bullet deformation there is, the deflection of the shot and the loss of energy of the bullet.

Don't forget that there are different types of glass too!
 
What would be the most important factor

In shattering glass.

The glass. Store window glass is often tempered, so that if little johny runs into it, the top part (which is now a .75", 200 pound razor sharp guillotine blade doesn't cut him in half. The amount of "temper" that the glass underwent would be the major factor. House window glass is usually not tempered and will break in large pieces or sheets. Auto glass is very tempered with a plastic binder layer. That is why it shatters violently into little pieces, but often in a confined area.
All else being equal, my money would be on a large, slow moving bullet like a 45Colt or a tuned down 45acp, or BP lead ball. I think that a high velocity round would just punch through.
 
Geronimo45 said:
My question was, if one wanted to shatter reasonably-thick glass with a gun, what would be the most important factor - velocity, bullet weight, bullet shape? What bullets would be more prone to shatter the glass than just punch a hole through it?
Click to expand...

DogBonz said:
The glass. Store window glass is often tempered, so that if little johny runs into it, the top part (which is now a .75", 200 pound razor sharp guillotine blade doesn't cut him in half. The amount of "temper" that the glass underwent would be the major factor. House window glass is usually not tempered and will break in large pieces or sheets. Auto glass is very tempered with a plastic binder layer. That is why it shatters violently into little pieces, but often in a confined area.
Click to expand...
The effect does depend on what kind of glass it is, but DogBonz is only partially correct. Tempered glass is tempered glass -- there are no "degrees" of tempering. If the glass is required by a building code to be safety glazing, it will be tempered. Period. Tinted windows on high rise buildings may be "heat strengthened," which is sort of a lower degree of tempering, but that type of glass does not shatter into small granules upon impact like real tempered glass. Tempered glass will not ... ever ... have a small hole through it if shot. The impact will cause the entire pane to shatter into little chunks, not jagged shards. That's why it is used for safety glazing.

Automobile glass for side and rear windows is fully tempered and does NOT have a plastic interlayer. It reacts to impact like all tempered glass -- it shatters into small granules. The windshields have the plastic interlayer, and they are NOT tempered. A windshield could have a bullet punch a single hole through it.
 
Is another big factor nobody mentioned: The angle of the shot. If the guy was at a great angle to the glass and the glass was strong and tempered it could deflect the bullet into a different direction. This is a well known problem addressed by officers who must shoot into tempered automobile glass often. Sometimes the windshield is at a great angle and the angle must be considered when aiming. The absolute best penetration would be at a 90 degree angle to the glass surface. At a great angle you could skip most rounds off the glass. Any shot should idealy be made at between 90 and 45 degrees to the glass to minimize deflection or change in point of impact on the other side of the glass, the closer to 90 the better.
 
I believe the type of bullet to be irrelevantwhen factoring the shattering of glass. As long as the bullet has the force to poke a hole, the rest depends on the glass.
As far as making a shot through the glass goes, the bigger, and more inherently stable the bullet the better. The collision with the glass will alter the bullet trajectory depending on he bullet type, and angle of impact. The best case would be a solid perpendicular hit with something slow and heavy like a .45-70.

Dan
 
I believe the type of bullet to be irrelevant when factoring the shattering of glass.
Click to expand...
When penetrating glass it is far from irrelevant. At a good angle it is not a deciding factor, however when at a less than ideal angle it plays a major role in how much deflection is imparted. The better the round cuts through the glass the less deviation the glass imparts through opposing force on the bullet and the less off course it goes. Yes a more powerful round at a better angle will make it less of a factor, however it will also endager other people in the same building and room even more with over penetration as well as restrict how fast follow up shots can be taken by the sharp shooter if the result is not ideal.
 
Glass is very hard, even though it doesn't have great strength. Higher velocity bullets would be more inclined to break up when hitting the glass - I'd go for a shotgun slug!
 
windows

I've a friend who had a NID with a 9 mm Parabellum pistol and punched a neat little hole through a house window. Can't say what sort of bullet was involved.

The pistol and the window both belonged to a client and they both had a bad case of egg on the face. It was a long time before we let him live it down.

BTW: Some (but not all) cars do have laminated glass in the rear window.
 
An early James Bond

had a scene in which Bond shoots a BG in an apartment from another. He has a partner who shoots first, shattering the window then 007 shoots the guy.
Not a real reliable source.
 
The funny thing about glass is that it's (a liquid) an amorphous solid. As such it has some rather amazing energy absorption/dissapation properties right up to the point at which it breaks. Slow motion film of glass objects breaking are fascinating and they have the same ripple effect you get from tapping a water balloon or watching the surface of a pan of water ripple.

As a result it becomes extremely difficult to judge how much energy it would take to -just- penetrate glass vs shattering it to bits. I don't think you can really say velocity vs bullet weight vs bullet shape independantly of each other because I strongly suspect it would be the effect of a number of factors joining together that would give more specific results.

Talking real world though, if I wanted to punch through glass (ESPECIALLY something like an auto windshield) I think I'd want my CZ-52 over almost anything other handgun I own.
 
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Yes, glass has no crystal structure. Amorphous is the word I think. It will tend to flow over (a long) time, but I wouldn't call it a liquid. Not sure if all safety glass is the same anymore though. Some slow motion would be good to see.
 
The first thing that normally happens to a rifle bullet ( HPBT/SP/FMJ) is that the jacket of the bullet gets stripped away and generates a shotgun cone pattern of jacket fragments and shards of glass after penetrating the glass. Please note that the glass fragments will always fly perpendicular to the surface of the glass, the bullet has no effect on this. The lead core of the bullet generally remains more or less intact and stays near the the same line of travel after impact.

The round loses a quite a lot of it's lethality and in the case of snipers dealing with commercial glass, doors and windows, there is usually two shooters involved or should be. They both aim at the suspect and fire a split second apart, so that the first bullet shatters the glass and may go on to hit the suspect, while the second bullet with no intervening glass has a clear path to the suspect.

A round striking glass at an angle, if not deflected, tends to curve inwards, due no doubt to the leading edge of the bullet on that side biting into the glass first and pulls the bullet in that direction, moving it off course.

Some Commercial safety glass shatters and react in a similar fashion to ceramic body armour inserts and absorbs the majority of a bullets energy.

So, unless you have no other option, shooting thru glass should be avoided.
 
Very similar subject matter, check out the "Buick of Truth" on the Box O' Truth website.

He found that the .45 ACP round had the least deflection when shooting through auto glass, both from inside and outside the vehicle.
 
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