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update page 2 how much fps you think !!!

Unread postPosted: Tue Aug 18, 2009 8:47 pm
Author: far_cry
this shot done with 650 psi approx (my gauge fucked up)

estimate the fps ( yes i have ggdt but i must hear your estimations )

things to know:
the shot done from distance of 17 meters
the camera was close to the soda can 2 meters approximately

watch the video several times( the impact ) . ignore the impact sound ,focus in the hit time

this video before slowing down

[youtube]http://www.youtube.com/watch?v=l8wkhbRRfcs[/youtube]

and this after

[youtube]http://www.youtube.com/watch?v=8d9FonrpEqk&feature=channel[/youtube]

Unread postPosted: Tue Aug 18, 2009 8:52 pm
Author: twizi
my guess 1000fps probaly more what diameter is the bb

Unread postPosted: Tue Aug 18, 2009 9:17 pm
Author: jackssmirkingrevenge
twizi wrote:my guess 1000fps probably more what diameter is the bb


I would say less actually, at 800-900 fps my air rifles (both 0.177" and 0.22") will literally tear the can open through hydrostatic shock - assuming this can was completely filled with water?

More details about the projectile would also be helpful.

Unread postPosted: Tue Aug 18, 2009 9:28 pm
Author: far_cry
actually it's not bb . it is a 8mm screw about 1.5~2 grams 4cm long

in the screw thing can any body weigh on scale this kind of screw (8mm base with slim body 4 cm long)


something like this

Image

and yes it was full of water.

edit: the screw hit the left bottom of the can , and look at the wood the screw damage it

thank you all

Unread postPosted: Tue Aug 18, 2009 9:33 pm
Author: jackssmirkingrevenge
far_cry wrote:in the screw thing can any body weigh on scale this kind of screw (8mm base with slim body 4 cm long)


Take a syringe, remove the plunger and block the nozzle and fill it with 4cm of water. Note the level of the water on the volume markings. Drop in the screw, and see by how much the volume has increased. New volume - old volume = volume of the screw, once you know this you just multiply it by the density of steel et voila, the weight ;)

I would estimate not more than 500 fps for your video, but without a chronograph and such an irregularly shaped projectile it's hard to tell.

Unread postPosted: Tue Aug 18, 2009 9:34 pm
Author: Technician1002
twizi wrote:my guess 1000fps probaly more what diameter is the bb


1,000 FPS makes shock waves in the water that rip open cans. This was quite a bit slower than 1,000 FPS.

My avitar was a water bottle impact in the 650 FPS range. It is true I used a little larger projectile, the the effect of the high speed impact is fairly well known.

I would guess that the impact is sub 700 FPS. It's hard to tell as the damage to the can can't be inspected in detail.

Unread postPosted: Tue Aug 18, 2009 9:36 pm
Author: far_cry
jackssmirkingrevenge wrote:Take a syringe, remove the plunger and block the nozzle and fill it with 4cm of water. Note the level of the water on the volume markings. Drop in the screw, and see by how much the volume has increased. New volume - old volume = volume of the screw, once you know this you just multiply it by the density of steel et voila, the weight ;)


or just put it on the scale !!!

Technician1002 wrote:
twizi wrote:my guess 1000fps probaly more what diameter is the bb


1,000 FPS makes shock waves in the water that rip open cans. This was quite a bit slower than 1,000 FPS.

My avitar was a water bottle impact in the 650 FPS range. It is true I used a little larger projectile, the the effect of the high speed impact is fairly well known.

I would guess that the impact is sub 700 FPS. It's hard to tell as the damage to the can can't be inspected in detail.


the shot was 17 meter long ,and the shape of the screw slice into the can .not like a marble

Unread postPosted: Tue Aug 18, 2009 9:39 pm
Author: jackssmirkingrevenge
far_cry wrote:or just put it on the scale!


I have a balance at work that can read to 0.00001 grams, but I don't have your screws so I was suggesting a method by which you could get around not having a suitable scale.

Unread postPosted: Tue Aug 18, 2009 9:44 pm
Author: theBOOM
Jack where can I get those types of scales... maybe not that down to the point but something that can measure .xxx grams ....

Unread postPosted: Tue Aug 18, 2009 10:04 pm
Author: jackssmirkingrevenge
theBOOM wrote:Jack where can I get those types of scales... maybe not that down to the point but something that can measure .xxx grams ....


From a laboratory supply store with a lot of $$$ :roll:

If you look around online though you should find plans to build your own scales that will be reasonably accurate.

Unread postPosted: Tue Aug 18, 2009 11:08 pm
Author: Technician1002
the shot was 17 meter long ,and the shape of the screw slice into the can .not like a marble


The fact that it made a hole the shape of the projectile indicates fairly slow speeds. The impact shock wave energy distorts the impact site at higher speeds as high amounts of energy is transfered in the impact.

Unread postPosted: Tue Aug 18, 2009 11:13 pm
Author: jackssmirkingrevenge
Technician1002 wrote:The fact that it made a hole the shape of the projectile indicates fairly slow speeds. The impact shock wave energy distorts the impact site at higher speeds as high amounts of energy is transfered in the impact.


I disagree there, the more the hole resembles the projectile's shape, then the faster it has to be going. Increasing velocity decreases the time which the target material has to distort and absorb the impact so the projectile simply punches straight through.

In this case however, we are talking about a water-filled container, so there are other forces at work here, by virtue of an incompressible fluid which is being displaced by the travel of the projectiles.

Image

Unread postPosted: Wed Aug 19, 2009 6:33 am
Author: Ragnarok
For reference, here's one I made earlier.
~8 grain domed .177" pellet at about 800 fps MV - range 5 yards (About 11 ft-lb on impact). Can filled to the brim with water.

Entry & Exit

The actual pellet impact can be seen in the middle of the first G. Contrast and compare.

theBOOM wrote:Jack where can I get those types of scales... maybe not that down to the point but something that can measure .xxx grams ....

If you need 0.001 gram precision, expect serious money. Also, expect it to fluctuate any time anyone moves anywhere within the room.

0.01 gram precision is probably more than you need, and those can be found reasonably easily online - or in the right stores.
I picked up a mini 0.01g one for about £30 at a store chain known as Maplin. Probably not the cheapest price for one, but it was a bit of an impulse buy.

Unread postPosted: Wed Aug 19, 2009 6:43 am
Author: inonickname
I have a nice scale (.001g) intended for weighing precious gems. I use it for the smallest pyrotechnic mixes that demand the highest precision etc. I also have a 1g increment scale (up to 5kg) intended for foods for mixing large batches of BP, star mix etc. I also use the .001g scale to monitor stars (a single star) to check when they have completely dried out. (stars are wetted to be pressed/primed- with alcohol and water- they need to be dried out before use).

I'm going to have to say the velocity isn't too great. Frankly, I've caused much more impressive damage with a Q-tip.

Edit:
Image
Image

Unread postPosted: Wed Aug 19, 2009 7:13 am
Author: jackssmirkingrevenge
Ragnarok wrote:Also, expect it to fluctuate any time anyone moves anywhere within the room.


You should see the one that reads to 5 decimal places :roll: it has to be mounted on a special table with a concrete block to make sure it's stable, and these balances usually come with an enclosed weighing area.

Takes forever to equilibrate but unfortunately for some tests you literally need 1.00 milligrams.