SpudFiles

I'm talking about a normal, 56 gram, 24mm steel Ball Bearing, hence the "BB" gun moniker. Velocity of ~1200 fps with 2400 psi nitrogen, ~1500 fps with 2200 psi helium.

3.5 miles/second... it will be interesting if we can make coilguns shoot that fast some day. NASA's LGGs work, but they are incredibly dangerous (4800 bar hydrogen @>5000 degrees Kelvin), and have horrible reload rates, and then there's the constantly fatiguing parts that get hit with a heavy piston going >Mach 1.

But I'll likely never get anything going that quickly, save some huge advancement in coilgun tech.

Well nasa's guns use a gunpowder charge to accelerate a piston pressurizing the hydrogen and expelling the projectile at enormous speeds. Things going that fast tend to behave more like liquids.

Sorry for going off topic but I found the documentary "Trinity and beyond" on youtube it chronicles the advancement of nuclear weapons.
There are 10 parts.

@DYI: I see your reasoning, but a ball bearing is not a 'true' BB. While the acronym is the same, BB is(as I'm sure you know) the size of shotgun shot between B and BBB sizes, coming out to 0.18" diameter, later specialized to the modern 0.177".

Most of us know how the varieties of LGGs work.

I did not say that I was using "true" BBs, I only used "BB" as an acronym. HEAL stands for High Efficiency Air Launcher, SCTBDC stands for Slow Change Trigerred Burst Disk Cannon, and, in this case, BB stands for ball bearing.

I know. I just enjoy ranting about anything to do with firearms

On the hairsplitting point, most guns that fire "true" BBs are not firearms, at least not by the real definition of the word. The legal definition really has nothing to do with what method of propulsion is used, and varies greatly. It's interesting to see how a paintball gun is actually considered a firearm in some countries.

I meant the fact that they were derived from BB shot, and in America(and most of the world), shotguns are firearms(okay okay, not muzzleloaders, but you get the picture). I don't mind considering paintball guns firearms, but only so long trade, possession, and carry are unregulated. Alas, this is not oft(if ever) the case; I feel for those in the UK and Australia; so sad /

Helium is popular as a balloon inflation medium so you shouldn't find it difficult or expensive to obtain.

Also, don't just see it as a way to go supersonic, but also as an easier way of propelling heavy slugs to high subsonic speeds. We have a tank of helium at work, about time I made a filling adapter for my toys...

JSR is right. If I could run the SCTBDC on helium at the same pressure as I already do with nitrogen, I could increase muzzle energy by over 1000 ft/lbs, using 2 pound slugs, a velocity increase from 401 to 448 fps.

By the way, how much do you think it would cost me for you to ship that cannonb...er ballbearing of yours to me Jack?

Also, this topic has the potential to become the longest ever in the pneumatic showcase. Seems like the username and topic name, and beautiful cannon made a good combination.

By the way, how much do you think it would cost me for you to ship that cannonb...er ballbearing of yours to me Jack?

Less than 25 canadian dollars, but I'll hang onto it for the time being if you don't mind, they guy who gave it to me is still waiting for me to build something he can fire it out of

I'm not seeing helium solely as a way of going supersonic, but it's effects are most pronounced at higher velocities.

For heavier projectiles, the effects are still there, but not so much.
Take a paintball, assuming all modifications go well:
Air: 237.5 J
Helium: 446 J
That's an 88% increase, Hydrogen (540 J) would be a 127% increase.
Refer to the 100g lead slug example, where the increase was only 5% for He and 6% for H₂. The effects are clearly hugely different at high speeds.

Part of the difficulty is I'm not sure about storage - I have no idea where I could put a largish high pressure tank.

I could obtain one or two myself if I was strongly inclined, but I can stick to 1" steel bar and cast Pykrete for now. The first Pykrete slug for the video has been in the freezer for a few hours now.

Ragnarok wrote:Part of the difficulty is I'm not sure about storage - I have no idea where I could put a largish high pressure tank.

A cheap solution would be one of the disposable ballloon inflation cylinders that can be had dirt cheap if you have a browse.

Not sure what sort of pressure they would be containing though, but perhaps you could go for a air/helium mix.

DYI wrote:...Also, this topic has the potential to become the longest ever in the pneumatic showcase. Seems like the username and topic name, and beautiful cannon made a good combination.

I'm posting because I want to be part of history

Seriously; I don't know if Wal-Mart has dominated Europe like it has America, but the helium fill stations can be found there in the party section. With that said, if Wal-Mart is not that global, I'm sure any credible party store will sell them. They are small and don't take up very much space.

Edit: I forgot to mention...Wal-Mart sells these kits for about $20.

@JSR & hubb017: Although those tanks are cheap, there's not much gas in them. It would last maybe 15 shots, which then makes it pretty expensive per shot.
If I want helium, I reckon BOC gases will be the source. I'll poke around a little.

BTW, Walmart owns ASDA in the UK, but it's an entirely different type of store to what Walmart is in the States.

@DYI: Hey, you're right, it could be the longest thread... I think the longest so far is BTB's sawn-off at 142 posts, and that's increasingly less far off.
I'm not aiming for that number, but I reckon that could be beat after I do my next video.

Still, all this is setting the bar pretty high for my next cannon.