SpudFiles

c11man wrote:should i still expect lower than mach 1?

Yes, you should still expect no more than 1000 fps. Like we said earlier, you should not expect that air will get you supersonic, regardless of the projectile mass or pressure.

ok so still subsonic...

about the wirenuts i remember what they are now! they are those things that you twist on 2 wires to keep them together right? if so i already have many of them (dad is kind of a electrition)

and the piano wire, if i go to true value and ask for it will they look at me like i am stupid and send me to a music store? also is it stiff enouth to chuck into a drillpress and file the point down?

still Does anyone have a way to harden steel?

c11man wrote:ok so still subsonic...

about the wirenuts i remember what they are now! they are those things that you twist on 2 wires to keep them together right? if so i already have many of them (dad is kind of a electrition)

and the piano wire, if i go to true value and ask for it will they look at me like i am stupid and send me to a music store? also is it stiff enouth to chuck into a drillpress and file the point down?

still Does anyone have a way to harden steel?

Piano wire is extremely springy.

To harden steel, heat it until it's cherry red and dump it into oil (yes, you could burn yourself)

Ragnarok wrote: As a general rule, assume if you're using air, regardless of pressure, you cannot exceed the sound barrier.
Obviously - before anyone links me to the Airforce Condor - there are some exceptions. However, these are few and far between, and somewhat (and logically*) exceptional.

well i did get a supersonic shots with air... simple "cannon" i made that was just connected to the huge compressor where i work. i think it is 2.000l and a pressure of 20bar. i just connected it to a 6m pipe in the piperack, then i opened the valve on the other side of the 20m 2" hose wich shot a hollow and very thin walled aluminium bar that i found in the lathe among the steel strips.
it was only 2m/s over the SOS so it might be the chrony but considering the hillariously light projectile and the chrony about 60cm from the muzzle it might have gone alot faster.

then you surely wonder why there is a 2.000l high pressure compressor, well the sandblaster is just as big.

i am in quite a hurry, but i hope you understand what i wrote.

what's your opinion? bad chrony reading or a good shot? mabe the dead space did something to?

SpudFarm wrote:what's your opinion? bad chrony reading or a good shot? mabe the dead space did something to?

Well, to know that, I have to know more about your cannon and projectile.

I'll also need to know the actual velocity and what the SoS was at that time - ideally, I would want to know the actual atmospheric conditions that day, but just the actual SoS would be passable.

Also, bear in mind, compression of dead space can only affect the SoS so far.

The chrony about 60cm from the muzzle it might have gone alot faster.

No, that's about the minimum distance to place the chrony from the muzzle of a cannon like that, based on the muzzle blast. Indeed, ideally, you would have actually put it at least another foot away.

The problem is with that chamber volume and pressure, it's very possible that the muzzle blast was large enough that you've got a bad chrony reading from putting it that close.

well we where inside and it was a warm day with some snow around the houses. so that would be humid?

i have allways gone out from a SOS of 335m/s and this shot messured 337m/s

if i placed the chrony further away i think the projectile would loose tremenous amounts of speed.

the barrel would be around 2" though i did not messure, i was just bored and the hose was ready so i just had to try before i left.

oh and the valve i opened was a 2 1/2" ball valve. the compressor was used a bit before i did this and it had less pressure then 20bar. i would say around 15bar.

anything more i could say?

SpudFarm wrote:i have allways gone out from a SOS of 335m/s and this shot messured 337m/s

Judging from your description of the day, I'd say the speed of sound that day was probably somewhat higher.
Under "standard-ish" conditions of 20 degrees C, 1 atmosphere and 60% humidity, the speed of sound is 343.6 m/s

You can't assume the speed of sound to be constant - particularly when dealing with such a close margin as this, where you really need to calculate it for the specific conditions.

Anyway, when you talk about the SoS being 335 m/s, that happens at around 5 or 6 degrees C, which doesn't really qualify as "a warm day".

if i placed the chrony further away i think the projectile would loose tremenous amounts of speed.

No, this is a common misconception. While the projectile is within the muzzle blast, it experiences absolutely minimal drag. As such, with an air cannon like this, the true velocity at 3 or 4 feet from the muzzle is seldom discernible by much at all from the true muzzle velocity.
Velocity measured within the muzzle blast will almost certainly read high however.

I'd say this is a combination of a high chrony reading from muzzle blast, and you not considering the actual SoS that day.

this sounds fair enough, but the SOS would not be that high, it was a warm day to the time, there was still snow etc.
i would guess 10 degrees C.

but atleast i got darn close.

and the thing you mentioned about the drag in the muzzle blast got me shamed. how could i not think of that?

SpudFarm wrote:this sounds fair enough, but the SOS would not be that high, it was a warm day to the time, there was still snow etc.

Well, I've been out in nearly 20 degree weather when there was still snow around... but those were very weird conditions.

and the thing you mentioned about the drag in the muzzle blast got me shamed. how could i not think of that?

Don't blame yourself. Many people don't consider it either.

Given the speed of the muzzle blast, the relative speed of air flow across the projectile is low, so drag is also low, and often actually negative - that is to say, sometimes the projectiles speed up slightly in the muzzle blast.

c11man wrote: i also want to harden the nail so i can penetrate things harder that wood.

Did you read my post about remington nails???, they are DESIGNED to Penetrate STEEL and CONCRETE....

I do chuck them up and reduce the head size with a grinder to reduce tailweight...

I use the 3" ones in my bowdart gun and at 50ft it will get full penetration on a dumpster, and sink to the head in 1" treated plywood at 70 yds...

I like the idea of the concrete nails.

Also;

Interesting conversation about the muzzle blast.

To further muddy the waters, I have this to add;

I actually fired my bbgun experiment without ammo from ~6" to the chrony, several times, at heights of 1"-3" above the front sensor.

The result...nothing. No error reading (when one sensor reads and the other doesn't, you get an error) and no velocity reading.

Fired with ammo, readings were taken that were consistent with expected results. I don't think lighting conditions had any effect, as at all times, I was shooting indoors with the light kit.

Makes me wonder if the chrony really can see the muzzle blast when using straight air. I haven't tried this yet with co2, but plan to do so the next time the chrony is set up.

With firearms, there is of course the issue of burning powder and lead/copper dust being ejected with the muzzle blast. These certainly would block light, and give a reading or error.

Perhaps part of the reasoning behind the recommended 5' minimum range?

oh sorry of forgot about your concrete nails.....
are these redialy availible at medium sized hardware stores? and if i ask for them do i just ask for concrete nails or what? also about how much does a package of 3inch nails cost for how many?

i dont have a chrony so i dont think i have to worry about getting error readings...

btw how much do you think a 3" and a 4" nail weights with the tail on it?

almost all hardware stores carry them, ask for remington nails, or powder actuated fasteners, FYI, they are also used to attach wood to steel I-beams(up to 1/2" thick), price for 3" are around $10 for box of 100...

ok so they are definatly affordable

now my only question is how much do they weight?

jeepkahn wrote:

c11man wrote: I do chuck them up and reduce the head size with a grinder to reduce tailweight...

.

Now that I've got hpa and co2, I have to leave the heads on them, otherwise they try to shed the orange collars/fins and loose stability... with 500psi I'm sinking them to the head in 3/16" plate stell from 70yds with 6"groups with no sights....