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sand filled backstop

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sand filled backstop

Unread postAuthor: c11man » Mon Feb 15, 2010 10:35 pm

for my new cannon (unposted and a sneek peek below) i am going to make a backstop so i dont always loose my bearings when i fully penetrate the intended target. my thought is to have a pywood box filled will sand to stop them, the front of the box is fairly thin so it wont provide much resistance. my question is how deep should i make the box to stop the 5/8 bearing at full speed (750fps) before it exits the back of it.

<a href="http://s696.photobucket.com/albums/vv321/c11man/bearing%20cannon/?action=view&current=fullcannon.jpg" target="_blank"><img src="http://i696.photobucket.com/albums/vv321/c11man/bearing%20cannon/fullcannon.jpg" border="0" alt="full bearing cannon"></a>

thanks, c11man
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Unread postAuthor: Lockednloaded » Mon Feb 15, 2010 10:41 pm

i think that box 'o' truth has done sand before, but firearms and airguns have huge differences in speed. I still recommend you check it out, could give you a rough estimate
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Unread postAuthor: deathbyDWV » Mon Feb 15, 2010 11:53 pm

If the sand is filled to the top so there is no room for it to move, then 4 inches deep would seem like enough...

I was thinking of some kind of back stop for my new hybrid also. My idea was something like a box of wadded up cloths first, then layer of thick rubber(from an old tire), then lastly a piece of sheet metal or something that wouldn't be penetreted... The idea is to make the bearing enter the cloth and hit the rubber to stop it. When it bounces back out, the cloth would catch it.

This would be put at the back of a box o truth setup.

Btw... I wonder what the gun in your signature will look like...<(insert sarcasm here) :lol:
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Unread postAuthor: c11man » Mon Feb 15, 2010 11:57 pm

well box o truth had all ammo stop at 6inches. i think the pistol ammo results are more relevent to me because all the rifle and shotgun ammo broke apart and i dont think my ball bearings are gonna split :D

anyone else have a different opinion?
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Unread postAuthor: D_Hall » Tue Feb 16, 2010 12:35 am

Well, at the office we catch 20 mm depleted uranium in a 12' sand filled cube. I'm betting that would work!


:D


OK, smart ass answers aside.... The military has been using sand bags to stop bullets and fragments of all sorts for a very long time. Sand bags are typically about 12" thick (in the dimension we care about). So while I don't know how thin you could get away with, it would seem that 12" would provide an upper limit to the problem.
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Unread postAuthor: jackssmirkingrevenge » Tue Feb 16, 2010 12:52 am

Looking good :D

Agreed with most here, 6-12" should suffice, looking forward to the damage pics/vids :D
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Unread postAuthor: inonickname » Tue Feb 16, 2010 3:24 am

I wouldn't even bother with sand.. To stop bearings from my coaxial I use a stand which has layers of clothing like thick jumpers, jeans etc. hung over it. They will stop the round very quickly as long as they aren't resting against something solid. If there isn't travel to absorb the enrgy they will go straight through.

Easier to retrieve them like that.
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Unread postAuthor: POLAND_SPUD » Tue Feb 16, 2010 4:36 am

AFAIK you can use water to make sandbags more effective
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Unread postAuthor: jhalek90 » Tue Feb 16, 2010 4:02 pm

um, my favorite backstop is a plywood box, with a thick canvas front, and a thin rubber behind the canvas, and the rest is filled with sand.

The bullet penetrates the cloth, and the rubber.... but only leaves a small hole in the rubber... resulting in little to no sand loss for the first few (20-100 depending on cal) shots.
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Unread postAuthor: sssssbooom » Sun Feb 21, 2010 3:10 pm

I always just use a phone book or 2. It has always worked for me but I have never exceed 140psi.
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Unread postAuthor: john bunsenburner » Sun Feb 21, 2010 3:19 pm

A heavy cloth, with one loose side should do the tricky really...
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