mobile chernobyl wrote:I have no idea when the video will be done - my friend is heading it up this time as I'm busy at school. It should be a good one though - the ceramic balls have certainly brought my gun closer to it's true potential!
Looking forward to it, though to see true potential I would argue that a hard subcaliber dart would be the ultimate
Great work! The high speed recordings make this soooo much nicer to enjoy the hobby...er...obsession maybe.
JSR - Do you have any mental reference to pneumatics reaching anywhere near mobile chernobyl's 1500fps + averages. How much influence does kinetic energy have to do with FPS velocities? I mean two spherical projectiles, one ping-pong ball, the other golf ball will have different results. And, oh yeah, APFSDS style rounds MUST be attempted.
mobile chernobyl - In image "3" of your OP it looks like you have a recoil dampener. You've got about a foot worth of rollback in your stand when firing. Have you tried blocking the wheels to see if you get significantly larger barrel rise?
GonzoInferno wrote:Great work! The high speed recordings make this soooo much nicer to enjoy the hobby...er...obsession maybe.
They not only make it more enjoyable, but with a camera like the Casio Exilim series - you can review between shots which is pretty valuable for shot to shot analysis and corrections.
GonzoInferno wrote:JSR - Do you have any mental reference to pneumatics reaching anywhere near mobile chernobyl's 1500fps + averages. How much influence does kinetic energy have to do with FPS velocities? I mean two spherical projectiles, one ping-pong ball, the other golf ball will have different results. And, oh yeah, APFSDS style rounds MUST be attempted.
"Pneumatics" can reach sounds greater than that of the sound speed in air. Your going to need high pressures, very efficient valves, proper acceleration distances and light gasses preferably like H2 or He. A light gas compressed air gun could easily match the performance of my combustion gun. However it's not going to be cheap to build and use. My gun costs just about nothing to use (it wasn't free to build however! lol) - which is why I really like the performance benefits of combustion.
A ping pong ball very well may be able to travel over 2000fps with my gun, but it wouldn't have much effect on it's target compared to a golf ball.
FPS is what influences kinetic energy of the projectile unless your referring to kinetic energy of the affecting force?
For each gun there is an optimal projectile weight to achieve the highest kinetic energy - that is sort of what I mean by "achieving it's true potential". Sure a golf ball can travel 500-800fps faster than my ceramic balls, but it's not going to be able to transfer as much kinetic energy due to it's density.
APFSDS darts will be attempted, I just need a better sabot system. I also want to lay out a spread sheet to get a nice CoG to CP ratio for stabilized flight.
GonzoInferno wrote:mobile chernobyl - In image "3" of your OP it looks like you have a recoil dampener. You've got about a foot worth of rollback in your stand when firing. Have you tried blocking the wheels to see if you get significantly larger barrel rise?
I originally had planned to use recoil absorption, but with this gun having a peak force of 7-8 kJ in it's design spec, I opted out. I will incorporate these perhaps in my future high velocity project, but that's a whiles off.
I don't block the wheels but I do usually provide blocks 1 foot behind the gun. They are always utilized. If I did block the wheels the barrel rise would be pretty bad - it's already 2-3" at 30-40 yards.
The epitome of a "hybrid", the Utron 45mm CLGG certainly proves that there is a stage at which recoil absorption becomes necessary:
I think as a community we have a while to go before we hit that point
GonzoInferno wrote:JSR - Do you have any mental reference to pneumatics reaching anywhere near mobile chernobyl's 1500fps + averages.
The Airforce Condor does just over the speed of sound using HPA and a high flow valve, as do some other high end commercial rifles, but 1,400 or so fps seems to be the practical limit with air. If you want to go higher without going hybrid, you have to use a light gas like helium or hydrogen as your gas source.
How much influence does kinetic energy have to do with FPS velocities? I mean two spherical projectiles, one ping-pong ball, the other golf ball will have different results.
Double the mass, get double the kinetic energy. Double the velocity, and you quadruple kinetic energy. Heck if you move water fast enough it will cut through steel.
The projectile is of course important too. As anti-tank kinetic rounds represent the epitome of high performance rounds, tet's take an advanced projectile as an example:
In order to achieve optimal penetration and range, the following parameters are important:
1) high velocity - if a projectile travels slowly, the target will have time to deform and absorb the blow without penetration, and therefore in order to penetrate well you need as high a velocity as possible. A typical anti-tank round is travelling at around 5,000 fps.
2) high sectional density - in order to maintain its momentum, and transfer the energy in a concentrated manner, you need a projectile that is as heavy and narrow as possible - this is why APFSDS rounds are made of very dense materials such as tungsten or depleted uranium, which being long and thin to give the distinctive arrow shape. This attribute also makes it very efficient flying through the air, remember that essentially what the prokectile is doing is "penetrating the air", so what makes it good to go through a target also makes it good to fly far.
You can see this with the golf ball/ping pong ball analogy, both have the same frontal area but the golf ball has higher sectional density so if you fire them off at the same velocity, it will slow down less quickly and therefore fly further.
3) high projectile hardness - nature will always choose the path of least resistance, so if the target material is tougher than the projectile, the impact energy will go towards shattering or deforming the projectile as opposed to the target.
4) optimal aerodynamic shape - this is especially important for high velocity projectiles:
As you can see, drag has a similar relationship to velocity as kinetic energy, so if you double projectile energy, it has to fight four times the drag.
The shape of the projectile dramatically influences drag, namely through the C<sub>D</sub> or drag coefficient:
It's clear that for the same velocity, weight and frontal area, a sphere would be subject to over 10 times more drag than an airfoil shape. This is why spheres are pretty terrible projectiles when it comes to retaining energy.
And, oh yeah, APFSDS style rounds MUST be attempted.
Note that using a sabot gives the best of both worlds - light weight and large frontal area inside the barrel, to give you optimal acceleration and high velocity, yet once the sabot is discarded, the subprojectile itself has high weight relative to its tiny frontal area, which makes it ideal for punching through the air and eventually the target.
The epitome of a "hybrid", the Utron 45mm CLGG certainly proves that there is a stage at which recoil absorption becomes necessary
A certain Mr. Hall might object to that assessment of Utron's puny efforts
Last edited by jrrdw on Thu Oct 24, 2013 1:52 pm, edited 1 time in total.
mobile chernobyl wrote:That's not really what set's it apart as I'm sure you know by now 10+Kpsi pre-ignition chamber pressures are just one of many things they've perfected.
My comment was tongue in cheek, they are definitely in same league - the awesome velocities they are achieving alone puts them right up there next to VERA as well as the fact that what they are doing can actually eventually be a viable weapons system.
One more thing (maybe two), are you concerned at all about sabot material flying close to the chrony? I have faced a similar problem and you really need to go back another good 5' or so to get out of the sabot range but it just makes it so difficult to aim. That being said, I'm surprised you managed to hit targets so far away; I thought the golf ball would move more than that in the air.
MrCrowley wrote:Did you film it all in one day? How long did it take to set up everything between shots?
One more thing (maybe two), are you concerned at all about sabot material flying close to the chrony?
What material are you using for burst disks now?
Yep - when I get a chance to shoot with the higher power stuff - it's at a "special" location and I like to get as much shooting in as I can in one day. So that basically means 4-8 shots until I manage to engineer a semi-auto cartridge-less hybrid lol.
I did some analysis of dry fire's and a golf ball shot to no where that were filmed with the high speed at 1000fps and the sabot material would be flying much faster than what number's were on the read out of the chrony. It's not a perfect measurement - but the velocity are right in the ball park of what you'd expect (somewhere around 80-90% of HGDT values).
I'm still using aluminum foil unfortunately - we experimented with one shot at the end of the day using .008" aluminum flashing but I actually got a "did not burst" scenario - where it did combust (and the chamber got REALLY HOT!) but the burst disc didn't. The foil is a fairly linear calculation for shear which makes calculating the burst disc layup rather easy - when you get to thicker materials you really need a controlled experimental value to determine the "K" value, or coefficient for the specific material your working with in this equation:
Since it's on the denominator side of things, and its a value from 0 - 1, it can have a great effect on Pb! I do want to look into a single ply solution for 10X shots however. It would benefit a lot of us because a lot of guns are in the 40-50mm bore size. However - I feel that the breach would need a better compression ring groove like in Larda's design to hold the burst disc in place and not have it torn out instead of burst.
Of course, there is also the piston valve
jackssmirkingrevenge wrote:Did I also see a VW van hulk with golf ball sized holes in it?
I wish, they wouldn't let me shoot it they also have a caravan camper - and being such a fan of Top Gear that I am - you can only imagine what I would do to that thing lol.
POLAND_SPUD wrote:did you shoot a perfectly functional refrigeration compressor ?? you murderer!!
Nope - well maybe. Most all of the targets I get are from a friend of mine's parents that recycle old stuff like that. The compressor was most likely neutered of all it's auxiliary items.
Thanks JSR for posting the video which apparently I just failed at because it's still a string of HTML tags lol...
I did some analysis of dry fire's and a golf ball shot to no where that were filmed with the high speed at 1000fps and the sabot material would be flying much faster than what number's were on the read out of the chrony.
Yeah I'd be confident your chrony numbers are correct. In my experience, sabot material usually resets the chrony reading instead of registering its own chrony reading. And as you said, the numbers are consistent across multiple firings with what you would expect.
Of course, there is also the piston valve
I think I would put up having to make burst disks for a 40-50mm union if I had a place where I could shoot the cannon often. It's going on 3 months since I last fired my piston hybrid; probably haven't exceeded a dozen firings over the whole year.