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Discussion Starter · #1 ·
I made this from a crutch from the Goodwill thrift store $4 for a pair. I grabbed tall ones that accommodate up to 6'6".

The front T and fork assembly is made from 1/2" schedule 40 irrigation pipe fittings.

The right forward extension is 3/8" longer then the left which is 3" long.

The crutch tip pipe was nearly 1mm larger diameter then the pipe fitting so that was a chore to widen. Tiny roughing on the end of the crutch pipe allowed it to be used as a really poor drill bit. Took near 10 minutes to drill the socket in.

I plan to drill and slot to accommodate tubes with 6mm airsoft bbs as anchors.

70" draw to cheek weld.

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Waiting on stronger tubes. Initial test with 17/64 steel and 1/2" steel with single Chinese 2050 band set 13" long at 70" draw or 537% length.

Help me out here is this 5.37 elongation or 4.37 elongation?

Are the relaxed tubes still too long? It is easy enough to shorten them.

17/64 steel 199fps at 19.44 grains 1.7fpe My old Red Ryder put out nearly 3fpe.

1/2 steel 160fps at 129.5 grains 7.36fpe I might be able to bust 20fpe with 5/8 steel and 3060 tubes.

Not using bigger ammo till bigger tubes are installed.

BTW the pouch is too big weighing nearly 150 grains.

Clearly I haven't posted enough detail for a full engineering study. But, feel free to ask questions and provide harshly creative feedback. I have more interest in improving the sarship than in deciding to be offended.

Cost: Crutch $4 with a spare remaining, PVC pipe and fittings $3, PVC glue $6 with 99% left over, Tubing and pouch $1.

So... Total cost is either $6 or $14 depending on your accounting methods.
 

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Tbh I think your crutch handle situation could be improved. The factory set up is bulky.

Also, I like to keep my elongation rate as close to 500% as I can. Sometimes I'll stretch a little bit more for a little bit of extra oomph but I don't like to max out my tubes. I feel like anyting over 500 is generally considered to be wasteful

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Discussion Starter · #6 ·
Correction on the old bb gun from my youth. It shot 4.5mm steel at about 5.8 grains approximately 300fps of perhaps 1.2fpe. Killed a lot of small birds with that one. Still noticeably weaker than a $2 Chinese slingshot.

Abenso: Are you suggesting 14" relaxed bands/tubes is going to get the 500% elongation you look for with a 70" draw, or are you thinking 11.67" gets 500% elongation at 70"?

For reference I shot the same 17/64" steel out of my pocket shot and got 280fps for a 40.7% speed increase and about 98% power increase so the pocket shot is hands down winner at the initial stage of development for the starship. The pocket shot is also easier to carry casually.
 
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