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"Adjustable Weight" Compound-Round

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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"Adjustable Weight" Compound-Round

Unread postAuthor: High-PSI » Sat May 14, 2011 6:48 pm

Hey Guys,

I need a heavier round than the normal 178 gram compound round. So, I was planning on making my own end caps that are heavier. I even emailed the manufacturer about making heavier caps for me. They are open to doing it. But, I wanted to figure out how to experiment with the weight of the round searching for the ideal weight versus recoil I would feel (for those who do not know, I fire these from a pneumatic cannon at 230psi and the kick with a stock compound round is intense, but not unbearable). Anyway, I had a brain-storm and decided to go on-line looking for something to add to the round to add weight and this is what I came up with.

These are simple 2 inch OD, 1/4 inch ID fender washers I ordered from McMaster Carr. The washers weigh 18 grams each. I needed a longer bolt as well. So, with 10 washers and a longer bolt, this round now weighs 352 grams. I plan on experimenting with various numbers of washers looking for the maximum weight I can fire without hurting myself. As a side note, I just added a muzzle brake to my cannon. So, a heavier round should not be too terrible to handle.

Oh, also, I plan on wrapping electrical tape around the nose of the round, bringing it up to the barrel ID as a guide to prevent it from cocking in the barrel and scraping it. That should also help increase accuracy as it will help the round stay straight through the barrel.

Matt
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Unread postAuthor: shardbearer » Sat May 14, 2011 8:01 pm

Looks nice! Great idea. I dont know why nobody though of it before.
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Unread postAuthor: jackssmirkingrevenge » Sun May 15, 2011 1:11 am

Adding washers as shims was the first thing that sprang to mind when I read the title, simply but effective. What is going to have the misfortune of being on the receiving end of these monstrosities?
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Unread postAuthor: MrCrowley » Sun May 15, 2011 1:15 am

What velocity and energy are you expecting from these rounds? Have you put any calculations in to GGDT?

Would be interesting to see how well they still fly too.
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Unread postAuthor: jackssmirkingrevenge » Sun May 15, 2011 1:24 am

MrCrowley wrote:Would be interesting to see how well they still fly too.


They are longer and denser and the CG is even more forward, everything points to them being much more effective than the originals if they can still be fired at significant velocity.
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Unread postAuthor: MrCrowley » Sun May 15, 2011 1:29 am

300fps significant enough? That's what I got plugging numbers in GGDT.
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Unread postAuthor: jackssmirkingrevenge » Sun May 15, 2011 1:40 am

MrCrowley wrote:300fps significant enough? That's what I got plugging numbers in GGDT.


It's a velocity most airsoft rifles would be comfortable with, but it would be like getting shot by 1760 airsoft rifles at the same time ;)

I would say the sectional density would mean that velocity retention would be quite high, so trajectory wouldn't be so loopy in spite of the low muzzle velocity.
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Unread postAuthor: High-PSI » Sun May 15, 2011 7:28 am

I plan on test firing through a stack of plywood for starters. I have a bunch of 3/4 inch sheets here. I bet I could penetrate 6 sheets flat against each other. The exit hole would probably be 7 or 8 inches. A 178 gram round went straight through 2 sheets without even shaking the plywood. The exit hole in those was 4 inches. Oh, I have the plywood hole it punched in the youtube video I posted in the build thread. I should post a picture of it. It is cool. The piece of wood has the orange paint on it, it is domed to the shape of the round, has the 3 holes from the nose of the round as protrusions on the wood, and you can even clearly see the machining marks from the lathe work on the round. All that is embedded in the wood!

What I would really like to do is see what kind of damage I could do to a cinder block. :D

I bet it would shatter a cinder block without a problem.

So, at 300 fps, I wonder if it would be visible in flight? The 178 gram round was completely invisible at the 60 feet or so distance I was firing it.

Oh, I can go up to 300psi too. So, that would give me even more power. But, I want to test my tank up to at least 400 psi for safety before I go that high.

Matt
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Unread postAuthor: jackssmirkingrevenge » Sun May 15, 2011 3:34 pm

High-PSI wrote:So, at 300 fps, I wonder if it would be visible in flight? The 178 gram round was completely invisible at the 60 feet or so distance I was firing it.


Looking down the barrel, certainly. Have a look at the youtube videos for the larger USG compount rounds.
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Unread postAuthor: High-PSI » Sun May 15, 2011 4:33 pm

Yeah, I noticed that. I am so used to looking at my cannons (I have more than this one) that fire fast enough not to see the slug, that it is weird seeing it in flight. Of course, at a long enough distance, nearly any slug can be seen in flight from directly behind.

I wouldn't know about the view from directly ahead. :D

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Unread postAuthor: jackssmirkingrevenge » Sun May 15, 2011 4:39 pm

High-PSI wrote:Of course, at a long enough distance, nearly any slug can be seen in flight from directly behind


Even withsupersonic bullets though really its the trail that's visible. Still, looking down the scope on a sunny day I can see 800-900 fps 0.22" pellets in flight.
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