What are YOU building

[CpTn_lAw]

MMMh....I don't know any method of testing it before...but that doesn't mean there aren't any!
I just have a question...My piston gun works like a charm, but GGDT predicts over 551 m/s with a .2gram airsoft BB and a 1 meter barrel at 330 psi...that's not possible, is it? Because, so far GGDT has proven to me that it is pretty accurate; but 551 m/s, i mean, woaw that's way over the speed of sound....anybody got any idea?

[inonickname]

MMMh....I don't know any method of testing it before...but that doesn't mean there aren't any!
I just have a question...My piston gun works like a charm, but GGDT predicts over 551 m/s with a .2gram airsoft BB and a 1 meter barrel at 330 psi...that's not possible, is it? Because, so far GGDT has proven to me that it is pretty accurate; but 551 m/s, i mean, woaw that's way over the speed of sound....anybody got any idea?

That does sound very odd.

What were the things like co-ef and operating gas? maybe check the inputs and try again.

[Ragnarok]

No, that's undoubtedly wrong.

As a general rule, I treat GGDT as accurate, unless it's predicting above 300 m/s, where I assume that the number is probably high, and that the real result will almost certainly not be supersonic.

If Apocalypse (my own modeller) predicts supersonic - that's a different matter, because I know it takes into account things that GGDT doesn't.
However, Apocalypse doesn't predict supersonic very often - it's not particularly hard to get numbers in the 300-320 m/s range, but getting above that is far harder.

[CpTn_lAw]

Thanks Rag for clarifying. However, I think i might just have broken the sound barrier with a .2 gram BB. my new barrel is 6.02 mm copper ID, and pressure was 20 bars. there was an anormal whip sound, very high pitched (with some cool echo lol) i'm still doing a video edit and i'm trying to get a much footage as i can, but slow motion takes some hard drive space and editing is long. Be sure it will be posted in the coming few weeks.
Just a global pressure question, the entire gun is made of steel, brass and copper, (apart from the piston which is hot glue with grease) . The blow gun is rated to 180 psi, what can i safely use in a matter of gun pressure that won't break the body of the blow gun?

[Ragnarok]

Thanks Rag for clarifying. However, I think i might just have broken the sound barrier with a .2 gram BB.

It's possible with the right pressure, launcher design and a light projectile, but bear in mind, a supersonic crack does not mean the entire projectile has gone supersonic, just that parts of the air flow across it have.

Means it's bloody fast, but not necessarily supersonic.

[CpTn_lAw]

yeah well, i had never seen an airsoft BB go through 1/4" plywood...GGDT predicts 361.2 m/s and i guess that's pretty much correct. my piston weighs 7 grams, and slides in and back when i blow air with my mouth, and even pretty much seals with only air from my lungs. The only problem i have here is when i cranck up the pressure, the blowgun takes 1/4 second before the shot takes place, whereas with the ball-valve it was instantanious (1.2 ms). I think i must reduce my dead space...mmmh

[boom_o_matic_2.0]

I dont know of any. I tried Tractor supply, lowe's, ace hardware...I dont know where else...

[covey12]

well i know its not a bb, but i have gotten a lead pellet to go through 1/2in. plywood all the time with my 1000fps bb gun, and 1/8 steel too, aluminum i have only tested up to 15 coke cans and it went through all of them, so maybe a pellet gun would work better, by the way plastic bbs shatter when they go fast and hit something hard, just take a regular airsoft gun and shoot the ground point blank, so i doubt you could get them through plywood

[covey12]

Thanks Rag for clarifying. However, I think i might just have broken the sound barrier with a .2 gram BB.

It's possible with the right pressure, launcher design and a light projectile, but bear in mind, a supersonic crack does not mean the entire projectile has gone supersonic, just that parts of the air flow across it have.

Means it's bloody fast, but not necessarily supersonic.

that speeds will crack the bb once it hits a hard target, a steel or copper bb might be better

[Technician1002]

well i know its not a bb, but i have gotten a lead pellet to go through 1/2in. plywood all the time with my 1000fps bb gun, and 1/8 steel too, aluminum i have only tested up to 15 coke cans and it went through all of them, so maybe a pellet gun would work better, by the way plastic bbs shatter when they go fast and hit something hard, just take a regular airsoft gun and shoot the ground point blank, so i doubt you could get them through plywood

Gumballs shatter too, but it surprised me when one went through a sheet of 1/2 inch plywood. With enough power, he might make it.

Edit*** Added photo of the 1 inch coaxial cannon that shoots gumballs through the plywood. Blow gun trigger is used on another project. This cannon is retired as it was dropped once too many times and the muzzle coupler and reducer cracked and leaks. This cannon broke 3 pistons.

[inonickname]

Last portion of epoxy is setting up on my sniper.. Praying that the face will seal. It's a fairly hard rubber, which is why I suspect that it didn't seal 100% with the 2 psi my lungs make.

If it doesn't, I'll just salvage the pipes and make a qev in metals when I'm back at school.

[CpTn_lAw]

Okay, i reduced the dead space, put some o-rings rather than teflon tape, for the valve to be really serviceable. I have tried different ammo :
6mm glass BB : really fast, not accurate, explodes on impact making a glass-dust cloud.
6mm steel BB : Faster than my 800 fps pellet gun, goes through 3/4" wood at 11 bars.
6mm airsoft 0.25 : goes through 1/4" wood and badly dents the second 1/4" wood bar; oh, and i tried to shoot it at a hard rock (marble like) : there is a white spot where it hit, and i only heard little fragments go everywhere really fast.
6mm airsoft .12 gram : WTF? can't see were it goes, i only know that at point blank and 180 psi, it makes a serious explosion on the ground. past 5 meters, i can't see the impact.
6mm screw : fast, dangerous, doesn't fly very straight but cut 1/4" branch from a tree 100 meters away.

little aluminium foil ball, not compressed : flattens on impact and takes the shape of whatever detail there is on the target. I took some videos, back to editing

[Gippeto]

Sounds like you've got a winner there CpTn.

I know what you mean about the .12gram bb's. Mine penetrated ~3/4" into a directory even though they disintegrated in the process.

Have any .22 pellets?? Swage the skirt with an airsoft bb to fit. One of Jacks tricks.

When your friend gets the chrony, would you please do a "dry fire" over the chrony from ~6", to see if his picks up the muzzle blast? (You'll get an "error 1" reading if it does.)

Mine didn't, and I would like to see if that's consistent with other chronys.

Thanks.

[CpTn_lAw]

I'd love to have .22 pellets! I knew the trick before signing into spudfiles lol!! I am really surprised of the power benefit a piston gives compared to other valves(except burst discs for sure but they are a pain in the ***).
Today, i tried to shoot a glass BB....i shouldn't have lol, it must have jamed in the barrel and exploded sending tiny bits flying in the garden.
I did a video to prove that an airsoft BB vapourises on impact with marble-like stone. The plastic of the BB actually disintegrate and little particles get stuck in the stone impurities. (seems perfectly smooth by hand)

My blowgun currently goes to only 11 bars....it seems the actuator retracts in the blowgun body and i can't press it. I think i might get back to my 3/8" ball-valve actuator... I also added a neoprene disc on the sealing face of the piston and a screw to hold it in place, as the hot glue piston alone seemed to be ate by the barrel seal. Can't find my bike grease...and every other grease I find i the house is liquid, and gets wasted afetr two shots.

[Gippeto]

Mon dieu!!! You must have grease!!!

Pistons are great fun.

Waiting on the video/s.