SpudFiles

WoW very good looking high power gun is it very accurate?

Nice work Gippetto!
I love the sound it makes in the video, kind of intimidating if I say so.

Thank you for the kind words.

I'll try to answer your posts.

I'm not "in to" airsoft, the bb's were in the smallest package I could find (2000 rounds). As it is, I'll likely never use them up unless I do a vortex.

And I will NOT be shooting this at people. (Why won't you play with me? )

The piston assembly, barrel bushing and barrel support were made on a Smithy Lathe/Mill/Drill. Any cheap lathe will reproduce it.

Helium would likely be fun, but the only gas I intend to purchase is nitrogen for "another" project.

A fridge compressor sure would be nice right now though.

@Jack; I think those schraders were costing you significant pressure. My check valve cracks at 3 psi.

Are you thinking that the compression wave is registering on the sensors?

I have .22 pellets, I'll swage the skirts and try up close and a couple feet away. They should retain velocity much better than the airsoft bb's.

The fill set up was taken from a CO2 fire extinguisher. It was the "pivot" point for the plastic nozzle.

You'll find a picture here;

http://www.spudfiles.com/forums/high-pr ... 14027.html

@ Sticky; No, I wouldn't consider this to be accurate. The barrel bends under its own weight, it also "flops" around, and the trigger is,...let's just say TERRIBLE! The ergonomics leave something to be desired as well.

I'll be doing some tweaking and further testing on this, but I don't honestly expect to get much more out of it.

Version 2 (X-1.2) will be a heavily modified "Toolies" piston, and should, I hope, see some reasonable increases.

hmmm how can i have missed that fire extinguisher topic?!?!? now i just need to find somewhere that has loads of old fire extinguishers!

Yes, I believe that's what Jack's thinking. It could be that the muzzle blast is affecting the sensors. If you move back a foot or two, if the number considerably changes, then it'll be a symptom of that.

ALIHISGREAT wrote:now i just need to find somewhere that has loads of old fire extinguishers!

My house has a considerable collection. I have seven old 2kg CO2 extinguishers (about 3 litres internal volume), which will all be good for about 3000 psi after I finish my modifications.
Not entirely sure what they're all going to be used for, I've had them around for a long time without doing much to them. I was still thinking of making them into the ultimate mobile pressure source, joining them 5 together into a 100+ bar backpack supply.
They'd be capable of taking twice that pressure, but generating 200 bar is beyond my currently conceivable resources. The most I think I can build something to generate is 150 bar, and that alone would be quite a bit of work.

My house has a considerable collection.

yes but where did you get them from? i searched yahoo for fire safety/consultancy type businesses in Cambridgeshire so i may email a few.

ALIHISGREAT wrote:Yes but where did you get them from?

Nicked them out of a skip... well, not quite. My school was replacing all the old black ones with the new red variety, and I asked if I could have the old ones, as I was sure I could find a use for them.

Ok, I'll be taking the chrony to work tomorrow for a determinate answer to the muzzle blast question.

The manual recommends 5 feet from muzzle to chrony as "about right" for a .22 rimfire.

Quite different than the ~6" I was using.

Gippeto, if you're having that much trouble with the barrel plopping, you might think of sleeving it. Some 1/2" (Or 1/4" if you can get it) would fit loosely, and you could fill the space around it with two-part expanding foam or something.

What a difference 4 and a half feet makes!

The new results are in, and they're not as good.

Due to time constraints, I did not bother with the pellet testing, and simply fired the airsoft bb's from a 5 foot (muzzle to chrony) distance.

Velocitys of 1039fps and 1059fps were recorded.

It's been 20 years since I took physics, so it's unlikely that I will try to calculate the velocity at the muzzle. (Shouldn't be too different anyway.)

I will however, keep tinkering and trying to get a READING over mach 1. (With otherwise UNHEATED AIR of course. )

Gippeto wrote:It's been 20 years since I took physics, so it's unlikely that I will try to calculate the velocity at the muzzle. (Shouldn't be too different anyway.)

You might be surprised.

A quick calculation suggests that at those speeds, a 0.12g BB will lose nearly 200 fps over 5 feet, and even a considerable amount while crossing the chrono.

However, I stress that that doesn't take into account the fact that the highest velocity is usually attained after the barrel, due to some push from of the muzzle blast - and the fact that the projectile suffers less drag for the first couple of feet while in the fast moving air of the blast.
I recall seeing some data a while back that talked about the reduced speed losses in the first few feet after the muzzle on air rifles - might prove useful here in actually doing a rollback to the muzzle velocity if you're still interested. I'll need to remember where I found it though.

Damned, light weight spheres anyway! (Shakes fist at bottle of bb's.)

If you come across it, that would be great, but I'm not going to lose sleep over it.

Thanks.

Gippeto wrote:If you come across it, that would be great, but I'm not going to lose sleep over it.

Found it.

In PCPs, it's normal for there to be a gain of up to 1% velocity from the muzzle at about 12-18" past the muzzle.
Velocity is back to the muzzle velocity about 2-3 feet from the muzzle.

Assuming the same distances apply here (quite a large assumption to be honest, but I'll guess the weight is fairly insignificant, but the near super sonic velocities will be, these figures are at about 800 fps), you could be looking at a muzzle velocity up to 100 fps higher than the readings at the 5 ft mark.
If the assumption is near correct, that would put these results very near the sound barrier.

However, having seen these results, I would be fairly confident that for this particular "gun", you could shoot across your chrony at about half the distance without the muzzle blast affecting it, which would remove some of the drag from the equation - so I would move a couple of feet closer myself.
Bear in mind though, moving closer is only appropriate with some cannons. For example, I couldn't really do it with something like HEAL, because that has a visible muzzle blast a good 6 feet long, and if you look at the video, it's still shifting the backstop from twice that again.

But we're forgetting, regardless of whether it is actually supersonic, you're probably recording the highest confirmed velocities of any pneumatic.

I know JSR got a 1100 fps reading, but that was with a Combro right at the muzzle - and as we know, readings at the muzzle can be a bit dodgy. Not to mention that you're competing with a considerable amount of drag.
And I myself have recorded readings almost as high as you myself using paintballs (I think it was about 3 foot range across the chrony), but I'm not using a particularly reliable chrony (I made it myself... )and like I said, HEAL has a very vicious muzzle blast, so I can't lay any real claim down.

I agree with Rag that the decrease in speed even over such a short distance would be substantial for a projectile with a poor ballistic co-efficient like a lightweight BB.

Try it out with pellets, it won't be supersonic but it will do some hurt my PCPs at 850-900 fps with 16 grain pellets are quite a force to be reckoned with.

Thanks for doing that.

I'll still have to find some more "steam" in this thing, if I want the confirmed number.

I think I'll take it apart, and give the sealing end of the barrel a bit of TLC.

Yeah, HEAL has a vicious MB, no doubt about it.

So does the co-ax on unregged CO2. I can hardly wait to try nitrogen.


Edit:

Sure Jack, I'll try the pellets tomorrow. Benji domes 14.3gr, and see what it'll do.