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Unread postAuthor: McCoytheGreater » Fri Feb 12, 2010 3:16 pm

Nice. As you look for your endcaps, make sure they are dwv instead of sewer/drain pipe. I've had a sewer/drain endcap blow out on me once. It held up for a while, but on a cold day it will pop off.
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Unread postAuthor: Hubb » Fri Feb 12, 2010 5:02 pm

MAPP will net you slightly more power, but is it actually worth the extra cost? Just something to think about...
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Unread postAuthor: Spud Bud » Sat Feb 13, 2010 5:32 pm

Okay fellow spudblasters :lol: I have built the cannon but have ran into a little problem. I am getting poor performance out of my cannon. I was expecting a BOOM!! But only get swoosh.. It does not shoot very hard because i can easily see the spud when shot. I think the problem is that i dont have a fan installed at the moment because i haven'twent to radioshack yet to buy the fan and wiring.I have really long chamber(24''x4''dia) so i think the fuel is not mixing thorouly thus causing poor ignition. Any suggestion????
:cry:
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Unread postAuthor: spudtyrrant » Sat Feb 13, 2010 9:29 pm

Spud Bud wrote:Okay fellow spudblasters :lol: I have built the cannon but have ran into a little problem. I am getting poor performance out of my cannon. I was expecting a BOOM!! But only get swoosh.. It does not shoot very hard because i can easily see the spud when shot. I think the problem is that i dont have a fan installed at the moment because i haven'twent to radioshack yet to buy the fan and wiring.I have really long chamber(24''x4''dia) so i think the fuel is not mixing thorouly thus causing poor ignition. Any suggestion????
:cry:
I had a cannon that exact same size, with the exact same problem, and what it came down to was i needed a chamber fan and a more powerful ignition source(a burst disk also helps) once you get these items you should see a drastic increase in performance.
Hope this helps.
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Unread postAuthor: Spud Bud » Sun Feb 14, 2010 1:00 am

spudtyrrant wrote:
Spud Bud wrote:Okay fellow spudblasters :lol: I have built the cannon but have ran into a little problem. I am getting poor performance out of my cannon. I was expecting a BOOM!! But only get swoosh.. It does not shoot very hard because i can easily see the spud when shot. I think the problem is that i dont have a fan installed at the moment because i haven'twent to radioshack yet to buy the fan and wiring.I have really long chamber(24''x4''dia) so i think the fuel is not mixing thorouly thus causing poor ignition. Any suggestion????
:cry:
I had a cannon that exact same size, with the exact same problem, and what it came down to was i needed a chamber fan and a more powerful ignition source(a burst disk also helps) once you get these items you should see a drastic increase in performance.
Hope this helps.

I was thinking the same on the fan but the burst disk is another good idea. Correct me if i'm wrong but for the burst disks i can simply use masking tape or foil right? Right now i have a simple piezo igniter so i'm limited to only two sparks. At the moment i have just one spark right before the breach so i was also thinking that this was a problem as well. I wanted to place the spark in the middle but i was afraid of screwing in screws in just one layer of PVC. Is it okay to drill two screws in only one layer of PVC or will it weaken it too much?
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Unread postAuthor: jimmy101 » Sun Feb 14, 2010 1:30 pm

Spud bud: Here's an easy way to verify that the performance problem is caused by poor mixing and not something else (like too rich a mixture).

Fuel the gun and let it sit for ten or fifteen minutes. Perhaps invert it a few times. After that long the fuel air mixture will be fully mixed even without a fan. The gun should perform well if mixing is the problem. If the long wait doesn't help then you have some other problem. (This assumes your ammo is making an OK seal with the barrel, it doesn't have to be airtight, but it should be close.)

Mixing of gases can be a pretty slow process. Lower temperatures make it even slower. At 90F you often get OK mixing in say 15 seconds. At 40F the same fueling method may not fire at all after just 15 seconds.

McCoytheGreater said:
Nice. As you look for your endcaps, make sure they are dwv instead of sewer/drain pipe. I've had a sewer/drain endcap blow out on me once. It held up for a while, but on a cold day it will pop off.

Uh, "sewer/drain pipe" = DWV (drain-waste-vent)
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Unread postAuthor: McCoytheGreater » Sun Feb 14, 2010 6:18 pm

S&D pipe is thin wall, not SCH, and is crush rated versus pressure rated, therefore S&D is not equal to DWV. The S&D endcaps will fit in DWV endcaps, though. Thus the warning.
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Unread postAuthor: Spud Bud » Sun Feb 14, 2010 6:38 pm

Okay....I replaced the piezo ingniter for a new one because the old one created poor sparks.(It was about 2 yrs old :shock: )It now has noticably way more power than before but it is still not to my expectations. It is not able to pass through a 1/2'' piece of wood(not ply-wood) which i had as my target and shooting spuds as ammo. I hope the fan will give me the results i am hoping for...Here are some pics of the launcher
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Unread postAuthor: McCoytheGreater » Sun Feb 14, 2010 11:55 pm

Gniess. Looks much like the ones off burnt latke. A gold standard in spudguns.
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Unread postAuthor: Spud Bud » Mon Feb 15, 2010 1:31 pm

Here is a damage pic on 1/2in plywood.. Some went through but some just splattered on the wood. I think the fan will give me more consistent results and power.
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Unread postAuthor: jimmy101 » Mon Feb 15, 2010 2:58 pm

McCoytheGreater wrote:S&D pipe is thin wall, not SCH, and is crush rated versus pressure rated, therefore S&D is not equal to DWV. The S&D endcaps will fit in DWV endcaps, though. Thus the warning.

Learn something new every day ...

Drain pipe is ASTM 2729
DWV PVC is ASTM D2665
Pressure rated PVC is ASTM D1785

I don't think I've ever seen drain pipe or fittings at the local hardware stores.
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Unread postAuthor: Moonbogg » Tue Feb 16, 2010 12:56 am

Get a fan in that bad boy for sure. If possible, install a spark strip for even better performance. I would not drill through a single layer though.
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Unread postAuthor: Spud Bud » Wed Feb 17, 2010 5:59 pm

I installed the fan and what miracles does it do!! I currently have a 7ft4in golfball barrel on it and i think i need a longer barrel by like 12ft in sdr-21 1-1/2 dia pipe to get more performance. Right now i have a 30in long 4'' dia chamber with about a 1.8:1 ratio. I want to get the most performance out of it. I am considering spark strip as well Moonbogg.
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Unread postAuthor: artillerycreations » Wed Feb 17, 2010 7:43 pm

It all depends on what you want. If its loud and you like it that way then keep it how you have it. A 15' 1.5'' sdr 21 barrel gives you about a .89:1 c:b ratio which would squeeze a bit more power out of the gun.
You have to consider the fact that barrels that long, unless sleeved in 2'' sch 80(in which case it would be really heavy) would sag and droop and when it gets very warm outside, likely bend with some degree of permanence.
Its just not practical unless you mount it and why mount something that small. I feel pvc is light and has a more handheld feel to it. A 15' or even 12' 4'' barrel as you suggested is just not handheld.
Even if you went ahead and made the barrel longer, you probably wouldn't notice much more power and would feel it was a waste of time and money.
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