Going to tennis balls for class instruction of the sling...  any users (slingers or tennis players) out there that can comment on about how long they last before going flat/dead???  I know they make a "high altitude" version that's supposed to have a less permiable shell (leaks the air pressure inside at a slower rate) but I don't really want to pay the premium for them.   Guess we really don't care if it bounces right anyway unless we're thinking of rebounding off heads with occasional errant throws.   

Appreciate your reply... yes...  I guess the loss rate will exceed the flattening rate..   

We will have the boys stand right in front of a backstop to practice throwing.... one boy at a time while the others watch and shag any errant throws.   I have three 10 ft. by 10 ft. backstop panels... two are made for stopping golf balls and the third is 23 oz. canvas.  I have three frames for them...  two which are 1" schedule 40 pipe joined at the corners with plain pipe elbows.  For the Slingfest I'll use sockets made from 1 1/4" pipe that have a bullet (machined 1 3/8" dia. steel) point welded into one end.  I drive the sockets into the ground and simply insert the frame into that socket (1'' slides nicely into 1 1/4") and attach the backstop.  I'll pull the sockets with the tractor loader after we're done in Sept.  For the classes,  I am fabricating a crossmember with 1 1/4" vertical pipe sockets welded on the ends to hold one of those same backstop frames.  The cross-member attaches to a small utility trailer so when I arrive at a site, I simply screw the pipes on their elbows, insert the frame  into  the sockets and attach the backstop.   The mass of the trailer keeps everything upright but I also have the option of running guy ropes down from the tops and anchoring with 1" diameter steel stakes.  Oops... sorry... didn't mean to do a core dump on your question.   

Anyway we can park the trailer (and backstop) just about anywhere (yard, park, driveway, open field (gots lots of them here in Wyoming), etc.)

that is another thing i wanted to clear up for gunsonwheels, that when a tennis ball goes flat it still holds its shape.  not like a basketball will get all floppy all over the place.  i have punched holes in tennis balls for various applications and they still hold thier shape becuase they are made from ridgid rubber.

Thanks for the suggestion about sub-standard balls.  I'll have to go to the the big city to the North and see what I can find...

Thanks again.

Tint,
Why "environmentally unfriendly" re: tennis???... 'cause of all the balls it turns into "waste"?   Maybe we just don't have enough slingers in the world...   

cheap tennis balls sold for dogs last for about 5 minutes and then fall apart - whether this is due to slinging or the mastication they take from the dog - who can say. But decent tennis balls last huge amounts longer. When I can find ones that other people have lost :-)

Gunsonwheels,

I often practice with tennis balls indoors, 5-8 meters from a wall (squash court). The balls can go "flat" (don't bounce as much, make different sound) after just ten or so full power throws. After, say, 50 full power throws, they start to fall apart and become more like slinging a rubber sock. By that time it's a challenge just to load them in the pouch.

Slinging at a backstop that's not solid is probably the best way to go, sounds like you have an excellent set up planned.

I think it would be great to pin/clip/sew a small metal plate to your backstops (maybe just the canvas one) as a target.
Because the backstops are flexible and absorb energy, these wouldn't need to be super-sturdy designs. But they'd add motivation and feedback to training.

Tennis balls rather get out of sight than out of shape. I bought a 35 old house last year and we still find old tennis balls behind and under bushes. They look terribly but they are in shape.
For slinging I buy old tennis balls on the flea market here. They cost about 50 €cent and work very well untill vanishing in the bushes...

funda iucunda