# Catch box theory



## TimR (May 22, 2011)

I've been shooting into a sheet folded and hung over a frame, but after garbage pickup day this week I have a nice wood case from some sort of furniture the neighbor didn't need.

I've done some searches but not found much discussion on what to use to actually stop the ammo, without bouncing away or penetrating.

I'm assuming most of you use some kind of hanging fabric, as opposed to a mass of material.

How heavy do you want the material? Like a bed sheet, a tarp, a table cloth, cow hide?

More than one layer?

How far in front of the back (how far can it swing back before it hits a wall or my wood case)?

Do you weight the bottom to keep it hanging down?

Oh, and can I hit golf balls into it? <grin>


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## Crac (Mar 3, 2013)

My back stops are made from cardboard, string and old curtains or bedding.

In terms of weight, the fabrics are rather light. I use at least 3 layers often 4 but with an air gap between some pieces.

I have around foot to 18" of "give" to allow the shots to slow down more gradually.

I use spring loaded clothes pegs, more string and steel hex nuts to weigh down the bottom edge if required. The top edge is very well constrained... but the back stop is fairly large so the useable area is sufficient.

I wouldn't try using this as a driving range... but I guess you could build something much much better using similar ideas.


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## TimR (May 22, 2011)

I bought a large tablecloth at a thrift store today. It feels about twice as thick as a bed sheet. It was marked $3, a little more than I usually spend, but it turned out to be on sale half off.


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## treefork (Feb 1, 2010)

A single t-shirt hanging freely is the best. If you need to fill the entire cabinet width , do two side by side. Over lap in the middle to avoid a gap. Also a little trick is to hang them like a drape hangs. ie Where you start to get slight vertical creases . Better energy absorption and no bounce outs. Remember , no tension in the material or you will get bounce out or pentration of the material.


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## AlmightyOx (Mar 4, 2013)

It also depends on what kind of ammo you will be shooting and with what force.

If you're shooting 300+ FPS with 3/4 inch steel like some of the people I've seen, you'll want a heavier backstop.

Just make sure it is free hanging, and a common number I have heard for distance from the back is 3 inches to allow it to swing.

Hope this helps.

-Ryan


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## TimR (May 22, 2011)

It sounds like I've been planning massive overkill. I'll do some testing on lighter material first.


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## ZorroSlinger (Dec 12, 2012)

Whoaaa .... 18 inches of 'give' depth for backstop? (Crac forum member) You must be shooting massive lead at very high velocity!? My indoor catch box, I have 7 inches of 'give' depth with 3 layers of material draping down, 2 inches of separation between layers. Then attached to back wall of catch box, 1 sheet of rug material. The very front layer is tentacle-cut T shirts draping down, and the middle & 3rd layer, solid T-shirts. Again, the final rug piece attached to catch box back. The tentacle t-shirt layer help entrap the ammo, and lessen bounce outs, but the tentacles do eventually tear. I am thinking of maybe hanging tentacled medium thick twine rope as replacement.

This is Jorge Sprave's tank-like catch box which is not that big or deep. He is using somewhat thick rubber protection on front of catch box and tentacled heavy rubber strips as first layer. This looks okay for his heavy duty slingshot shooting but I am speculating, perhaps, not as effective for lighter shooting ... the light ammo might just bounce off the hanging thick rubber strips!?


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## reset (Apr 13, 2013)

Two t-shirts spaced about 2-4" apart and 3-4" from the back, free swinging as others have said works perfect for even quite powerful bands and heavy ammo. I have some carpet in the bottom too just in case lighter ammo hits the bottom to hard and bounces out from there.


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## Samurai Samoht (Apr 6, 2013)

TimR said:


> I bought a large tablecloth at a thrift store today. It feels about twice as thick as a bed sheet. It was marked $3, a little more than I usually spend, but it turned out to be on sale half off.


I did almost the exact same thing. Went to the thrift store and found a 6'X6' curtain for a few dollars. Was a couple times thicker than a bed sheet. I built a PVC frame about 3 ft wide and just under 5 ft tall and hung the curtain on it and it has worked perfectly. I can break it down and transport it anytime. This thing has taken thousands and thousands of hits, everything from 1/4, 3/8, and 1/2 without making a rip in it.


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## tradspirit (Jul 23, 2012)

Cutting the tee shirts into stips after they are hung works well to catch the ammo and prevent bounce outs. I use two layers of "tentacled" tees with two inch separation and about a 4in distance from the back side. I have them draped over cords tied parallel to the front. I also tie a cord accross the front of the box and use it to hang squares of leather that provide spinner targets that always reset and hang back down when hit. Can are either hung from the front cord or placed on floor in front of the tees.


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## TimR (May 22, 2011)

For any given material, the longer it is the more it weighs, and so the more tension in it.

My box is about 3 feet square (I'll measure it later). Three feet of a bed sheet hanging down weighs something, three feet of a table cloth weighs something else, 3 feet of a beach towel, etc.

That affects the mass of the curtain (momentum transfer to the fabric) as well as the tension on the material (momentum shed to gravity).

The rate at which we shed momentum must determine the force applied to the material, and whether it tears or is penetrated.

It seems like I should know how to do the math for this, pretty sure we covered it in engineering school, but that was several decades back.


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## Jaximus (Jun 1, 2013)

TimR said:


> For any given material, the longer it is the more it weighs, and so the more tension in it.
> 
> My box is about 3 feet square (I'll measure it later). Three feet of a bed sheet hanging down weighs something, three feet of a table cloth weighs something else, 3 feet of a beach towel, etc.
> 
> ...


When I read the title "catch box theory" this is what I thought I was getting into. We need some schematics, diagrams, formulas. Where are all the physicists? Where are my textbooks? I'm going to need a study partner, I'm dyslexic.


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## TimR (May 22, 2011)

I did some experimenting after work tonight.

I let a bedsheet drape over the edge of a table with some weight on top, and shot at it.

Hit it, too, but then I wasn't very far away.

With a single layer of bed sheet, hung 24 inches down, the marble stopped and dropped. I was quite surprised.

I'm not shooting very hard. I started very light (old shoulder injury) and am gradually increasing band strength. I've measured the marble in the 220 fps range and half oz lead in the 130, but I'm not sure I believe those numbers. They seem way too fast for how hard I'm pulling.

I hung two layers of bed sheet and 12 inches of hanging sheet stopped the marble, as did 12 inches of a bath towel and about the same of the tablecloth.

So while I'd like to be able to still do the math, apparently this isn't such a difficult problem after all. Just about anything works.


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## Aussie Allan In Thailand (Jan 28, 2013)

Well I use very ammo 20 to 35 gram lead, and shoot double .04 latex or triple TBG; stretched to 550%.
So likely my backstop is overkill for many.

But use a super sized (2 person) heavy beach towel, doubled over to be a single person size, hung from a wire so it is maybe 3 inches off the ground, then for a target originally I had very heavy flattened cardboard boxes, on which using a marking pen I could mark in targets for accuracy.
After getting sick of hitting the same places all the time, I went to 4 rows of flattened steel cans, for the thrill of the sound and the dents, and sometimes/often the penetration. So now there are 8 cans a row X 4.

And nothing ever gets through, even the rare miss of the cans, through the cardboard, into the toweling. The misses are always the lead weighted hex nuts, not quite properly centered exactly in the pouch. As anyone knows who has shot hex nuts, not exact centering in the pouch, and they can go anywhere.

Cheers Allan


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## Crac (Mar 3, 2013)

ZorroSlinger said:


> Whoaaa .... 18 inches of 'give' depth for backstop? (Crac forum member) You must be shooting massive lead at very high velocity!?


 :thumbsdown: :naughty: :violin: :angrymod:

"children's wooden toy" 

1. I need something that does the job.

2. I need some space to work, no rig lasts forever.

You're right I'm sure it's overkill...


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## ash (Apr 23, 2013)

T-shirts are great at this job and so easy to find/use.

Tentacles or slits work really well to stop bounce-outs, but they wear out and tear really quickly. My latest theory is to use a long length of fabric (speaker cloth in my case, because I have lots of it) (ps - or multiple t-shirts threaded onto the same rail) and fan-fold or pleat it onto the hanger rail like a shower curtain: /\/\/\/\/\/\/\/\/\/

I think/hope that the folds will be very effective ammo decelerators and catchers. They should also catch shots deflected sideways dead in their tracks, last a long time and not be prone to ammo bouncing directly out like you get when firing small or slow rounds at a heavy cloth.

With regard to engineering guff, you want a barrier with high damping and low stiffness. Stiffness = bounce-outs. Heavy cloth, weighted cloth or dragging on the bottom = bounce-outs.


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## TimR (May 22, 2011)

I built the thing last night and again today.

It's mounted in an entertainment center cabinet the neighbor discarded, and is 28 inches high and 33 wide.

I put the first bed sheet 3 inches from the back and the second sheet 6 inches, by drilling holes in the sides and running a piece of steel 1/2 inch electrical conduit through.

And shot a marble. SMACK! It hit the back wall. My table experiments were flawed, because under the table there is no back wall.

So I installed another rod, this time 9 inches in front. A single sheet stopped the marble before hitting the wall. Success.

Then I tried a towel. The marble makes a huge dent, I think the weight of the towel gives it too much resistance and I may eventually get penetration.

I now have three layers at 3 inch spacing, with the first two being bed sheet material and the last a thick motel towel. (which I bought at a hotel sale) That should stop anything I'm ever strong enough to draw.

I did discover it is important not to let the fabric drag on the bottom.


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## Adirondack Kyle (Aug 20, 2012)

This is my set up, nothing escapes this catch box, I think I lost may bee 10 round all summer. Its PVC, blanket, and cooler


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## TimR (May 22, 2011)

What happens if I actually manage to hit the can? Does the ammo bounce away and get lost?


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## Adirondack Kyle (Aug 20, 2012)

It goes right in the box. , haven't lost any shots at all, the way the blanket is positioed behind the can, no matter how it hits, it always gets directed to the box


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## LittleBear (Mar 24, 2012)

Torsten band speed video great example of how effective a nice light looses hanging bed sheet can be.






:lol: 100 Meters per Second = 328.0839895013123 Feet per Second in the spare bed room, my wife would skin me alive if she caught me.


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## Aussie Allan In Thailand (Jan 28, 2013)

Hey I don't even have one yet, and my wife hits the roof with every dollar, or Thai Baht I do spend; BUT I do spend alot.

So I know EXACTLY where you are coming from; still you are among the best anyway.

Keep up the great work.

Cheers Allan


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## TimR (May 22, 2011)

I had trouble with bounce out.

Out of the first ten marbles I only recovered four.

I removed the second hanging sheet, and so far have recovered all of the marbles, but still a few had bounced out a short distance in front.


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