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SDR-21 for a noob

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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SDR-21 for a noob

Unread postAuthor: LongT » Sat Sep 06, 2008 8:49 pm

OK, so I saw a couple of size posts on SDR-21 AFTER I searched high and low and went across town to buy a stick of the hallowed stuff.. So... the golf ball... Just how tight is it supposed to fit? It's a little tight and I'd be bummed if the sucker blew up in my hands... If I sand out the inside will it screw up the PSI rating? Any thoughts? Thanks, T
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Unread postAuthor: CasinoVanart » Sat Sep 06, 2008 8:58 pm

Hey Long-T, how much force is required to push the ball down? Can you do it with one finger?

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Unread postAuthor: explsvcookie257 » Sat Sep 06, 2008 9:24 pm

A potato is way tighter then a golf ball in an sdr21 barrell.
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Unread postAuthor: frankrede » Sat Sep 06, 2008 9:31 pm

A golfball should fall down sdr-21 pipe with no force needed.
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Unread postAuthor: LongT » Sat Sep 06, 2008 9:42 pm

CasinoVanart wrote:Hey Long-T, how much force is required to push the ball down? Can you do it with one finger?

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Nope.. I have to jam it pretty hard in spots.. I'm wondering if I just got a bad stick of it. Some spots seem tighter than others. It was laying outside in a pipe yard all summer down here in central Texas.. Wonder if it warped in spots..

Thanks! I wish I'd never discovered this whole deal.. On a whim, I built my first one for my kid to cheer him up after his girlfriend dropped him in the grease.. I figured, nothing will mend a broken heart quickly, but launching a potato a couple of hundred yards is something to be happy about. Anyway, I built it, now I'm hooked..

Since I'm a golfer, I decided to build a pnuematic GB gun for myself, small enough to hide in my golf bag. In the mean time while I'm researching pnuematics, I decided to make an interchangeable barrel for his combustion gun. Thats where I'm at now.
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Unread postAuthor: Pilgrimman » Sat Sep 06, 2008 10:18 pm

Nope.. I have to jam it pretty hard in spots.. I'm wondering if I just got a bad stick of it. Some spots seem tighter than others. It was laying outside in a pipe yard all summer down here in central Texas.. Wonder if it warped in spots..


I think that's exactly it. I've had the same problems.
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Unread postAuthor: explsvcookie257 » Sat Sep 06, 2008 10:28 pm

you might have a golfball that is one used for cheating in a way there just a slight bit bigger ive had this problem and cracked the end of my barrel trying to smush it in.
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Unread postAuthor: frankrede » Sat Sep 06, 2008 10:53 pm

You should never leave PVC exposed outside for too long!
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Unread postAuthor: starman » Sat Sep 06, 2008 11:41 pm

I've found that not all SDR-21 1.5" is the same...basically one has a little too thick walls. The golfball should fit very easily...the thinner wall model. Keep looking for the right stuff. Also, BCarms can supply it if you so desire.
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Unread postAuthor: LongT » Sat Sep 06, 2008 11:48 pm

Thanks guys. I appreciate the help. I'll post a picture of my effort when it's together.

T
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Unread postAuthor: SpudFarm » Sun Sep 07, 2008 6:18 am

in my hybrid some balls fit and some not, try some other brands of golf balls
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Unread postAuthor: clide » Sun Sep 07, 2008 11:27 am

Most of the golf balls in the US should be the same size 1.68" which is the minimum size given in the rules. There is no rule against making them bigger, but that would just be stupid since it adds air resistance. I have ran across one that was bigger, but they are extremely rare. A little more common are golf balls that are slightly smaller. These golf balls are from countries with different rules, and were probably imported from cheaters wanting a little edge.

Basically the golf ball isn't likely to be your problem. The ID of PVC pipe has very loose tolerances so you could easily just have a piece with thicker than normal walls. If it is fine and some spots but very tight in others then you may be right about the warping.
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Unread postAuthor: SpudFarm » Sun Sep 07, 2008 11:37 am

i have a bag of golf balls that i (stole) found on the golf track.. all used for range, but some of them rolls through my barrel and others have to be hammered in..


LongT: mabe you should lathe it out or use a dremel? if it is only at small spots it is tight you can get a tight fitting steel slug with sharp edges and force it through
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Unread postAuthor: LongT » Sun Sep 07, 2008 2:39 pm

OK, I sanded the inside with a sander plug (giant hassle). It's pretty uniform now.

The ball still doesn't roll through by itself, but if I stand the barrel on one end, put the ball at the top and help it by raising the tube about 6 inches and drop and bounce it off the floor, it will move all the way through to the bottom in 15 or 20 taps. Do you guys think that's still too tight?

Am I ready to test or should I keep sanding until it rolls from top to bottom with no help?

Thanks,

T
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Unread postAuthor: psycix » Sun Sep 07, 2008 3:20 pm

Thats tight, but I guess that the insane force worked out by the pressure is not much compared to the friction it has.
Also note that the difference in balls can be larger then the difference in pipes.
How many different balls have you tried?
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