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PostPosted: Wed Jun 01, 2016 2:50 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
So I've finally got the reversed dropped bottle adapter block made for my QB78D, using a 13ci regulated Ninja bottle from Scopes & Ammo. It's been a long wait, since last summer, but I finally got the 7075 aluminum, got the holes machined and threaded for the bottle and for a Foster QD coupling at 45 degrees to connect to the angled nipple on the gun. Still have to make a rear bottle clamp to get it rock solid on the gun, but with the play available in the QD fitting and a stainless strap bolted over the brass fill plug on the main cylinder I went ahead with a clamp and carved cradle block between the bottle and the main cylinder and did some testing. Everything's solid with this temporary setup, just not very field-worthy with a big clamp hanging off the rifle.

Now to specifics with my question. I just had the 1.8K burst disc fail. I had done tests earlier today up to 1,200psi, as I tried various shims in the regulator to try and find about 1,000psi regulated pressure. Without an output gauge rig handy I resorted to low pressure fills and test firing, comparing to my notes on velocity at pressures between 600psi and 1,400psi with the QB. I know the gun maxes out at 742fps with JSB 18.13gr, at about 1,400psi. But that's too much energy for HFT targets (don't want to bend the steel), so needing to knock it down to about 700fps (just under 20fpe) I worked on the SSG and hammer weight until arriving at that lower power just about exactly at 1,000psi.

In my testing today, I was somewhat dismayed to see velocities starting at about 672fps then falling slowly on each shot, from a 1,000psi fill. Why would a regulated 1,000psi behave differently from just filling the stock-size main cylinder to 1,000psi? It should provide identical power with the same pressure. So my guess what that the regulator with a couple of thin shim washers was still well below 1,000psi, and I added another thin washer. Nope, still around 670fps. Was the regulator not working at all? So I pumped to 1,200psi. Got this string:
711, 713, 703, 701, 698, 703, 697, 695, 689, 692, 687, 686, 682.

Huh. 13 shots, mostly decending, but only a little at a time as I'd expect with the larger bottle. Not definitive though, so I tried pumping to 1,400psi to run a longer string. The Gehmann FX pump gauge and the Ninja's gauge had matched exactly at every level from 0 to 1,200psi so far, so I was beginning to rely on just the pump gauge. The instant the pump reached the 1,400psi mark the 1.8K burst disc blew out. Okaaaaaaay.....

So I removed the clamps, unscrewed the bottle, and unscrewed the burst disc bolt. Not being familiar with what's inside one (never used a device with one installed before) I don't know what's in there before it fails, but it looks clean and polished. I'm guessing a plastic disc of some sort was there, but was blown out one of the vent holes? Anyway, it plainly blew at 1,400psi, not 1,800psi, so the regulator must be too high with the current shimming and I've somehow misunderstood my shot strings in these early small tests. Perhaps there is something magically different about 1,000psi regulated and unregulated, but what that might be escapes me. I've talked to a guy at Badlands in New Westminster and he'll be happy to pressure test the regulator and adjust it for a small fee, but is out of 1.8K burst discs at the moment, expects them in the next few days.

So until then I'll be refining the drop block cosmetically, deciding whether I want to carve a small bipod mount Weaver rail section at the bottom (but probably not, never shot with a bipod so far and probably won't), making the rear bottle mounting part to secure it to the grip frame, and painting the various fittings with appliance epoxy and baking those hard. Once I get the regulator output sorted at the paintball shop I'm hoping that'll be the end of my misadventures with this stupid bottle, and I can just get on with having a lot of shots per pumping session. And up my pumping game too, as it's a bit of a workout filling this 13ci bottle!

But this burst disc thing bothers me... I mean, even if I did adjust the regulator spring shims much too high, that shouldn't have caused a burst disc rupture until at least 1,600psi according to many posts by Bob Sterne and others. They're not a precise device, I get that. But 1,400psi? That just seems way too low to fail, regardless of whatever else is going on. Anyone got any comments about this?


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PostPosted: Wed Jun 01, 2016 9:32 pm 
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Location: Coalmont BC
Some recent runs of 1.8K burst discs seem to be failing well below 1600 psi.... I have no suggestion, other than to complain to the supplier....

Bob

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PostPosted: Wed Jun 01, 2016 9:35 pm 
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Location: Vancouver
Wow. Well with proper testing my regulator won't be set over 1,000psi, so even if the next burst disc fitted tops out at 1,400psi it should be safe enough. I hope. Thanks again Bob.


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PostPosted: Thu Jun 02, 2016 6:24 am 
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Location: 123 gun street Nova Scotia
most i have seen are a very thin copper/brass like metal . ive never had one blow under 1800psi . others lasted over 2200.


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PostPosted: Thu Jun 02, 2016 6:42 am 
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Location: Dowling ,ontario
Gerard,
Ive had the same problem with the 1800 psi burst discs faiing at 1400 psi .I won't mention who I got them from ,because it would seem like bashing. I find the burst discs from Ninja seem to be the better quality, or acquire them from a dive shop .

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PostPosted: Thu Jun 02, 2016 9:58 am 
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Location: Vancouver
So not from Badlands Paintball? My bottle is from S&A, with a Ninja logo on the gauge so I assumed, perhaps incorrectly, that it's a Ninja bottle. Seems unlikely non-Ninja parts would be installed on a Ninja bottle. But maybe a true Ninja has their logo painted on the bottle itself? Ah well, guessing will get me nowhere. I'll get a burst disc replacement and the regulator set correctly and go from there. If it fails again I'll do what you guys do, hunt down a better disc.

And yeah, metal - I pulled out the 5K one yesterday and saw it's got a little brass-looking wafer in there, shape a spherical section, perhaps because it's already been under pressure. Gave me the impression of thinness, like shim stock.

Meanwhile, got the block painted and baked along with the stainless strap which wraps around the fill plug and bolts into the block sides. Made an aluminum disc to use in attaching the back of the bottle to the grip frame, but it proved too thick to fit and I'd have had to epoxy it to the bottle to make it work. Showed me where to correct dimensions though, so I'll braze together some steel for a slimmer version with a narrow band around the edge to cup the bottle base. Probably JB Weld that on anyway, just to make it rock solid.


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PostPosted: Thu Jun 02, 2016 1:57 pm 
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only thing to do is slap in a new burst disc and try again if it fails then your either exceeding the 1.8k max psi
or your Reg is not working properly..... :wink:

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PostPosted: Thu Jun 02, 2016 3:14 pm 
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Location: Coalmont BC
Ace, you are assuming the burst disc is within a normal tolerance.... I have found that they used to sometimes fail at 1600 psi (even when new), and after a short time sometimes failed at 1500 (I assume from metal fatigue).... although I generally find I can use a 1500 psi setpoint successfully with a 1.8K disc for years with no failure.... Many shooters have recently reported brand new 1.8K burst discs failing at about 1400 psi.... which I would suggest is less than acceptable, based on how they have performed over previous years.... I do not know if this is restricted to any particular brand or not....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Fri Jun 03, 2016 10:57 am 
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If your able to get your supplier to let you know the batch # you will be able to narrow down a more reliable burst rating. Burst discs are supposed to be designed to be within ~5% of their rating.

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PostPosted: Fri Jun 03, 2016 4:07 pm 
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rsterne wrote:
Ace, you are assuming the burst disc is within a normal tolerance.... I have found that they used to sometimes fail at 1600 psi (even when new), and after a short time sometimes failed at 1500 (I assume from metal fatigue).... although I generally find I can use a 1500 psi setpoint successfully with a 1.8K disc for years with no failure.... Many shooters have recently reported brand new 1.8K burst discs failing at about 1400 psi.... which I would suggest is less than acceptable, based on how they have performed over previous years.... I do not know if this is restricted to any particular brand or not....

Bob


your correct Bob I was assuming it was within the normal tolerance, or maybe they figure bursting at 1.5 or lower is safer
because normal output is 850 max on most tanks unless its a high output reg tank to begin with...
interesting maybe there getting stingy with there internal material....lol
or just an unlucky bad batch,

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