We shot into a box of vermiculite (insulation) and shot 50 BMG and down, box was a 2' x 2' x 8' (R & D range). Our sand back stops deformed projectles. It would strip the gilding metal right off the bullet.

As I recall MythBusters did a sequence about shooting at someone under water; and as I recall 3-4 feet was enough to slow the bullets used to the point where a swimmer at that depth or more would be safe----but not sure what cal/cartridges was used. 
 What would be safe for say a 223 might be a lot different than a .50BMG.  
I'm wondering how a softer than standard long block ballistic gel would work.  I'm thinking a succession of mediums with softer ones in front and denser ones farther back to slow the bullet progressively might not avoid deformation

sources:  Just google "ballistic gel"   
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you can buy it on amazon

Cat_Whisperer wrote on Feb 25^th, 2014 at 6:01pm:

That's what I recall too!

bpjack wrote on Feb 25^th, 2014 at 11:36am:


Yes I had thought of that, Jack.  The bullets go so fast I can't see them. Running on water at full speed while looking up................... well......

Have access to places where I can shoot from the bluff down to the water. Distance would be in the 400-600 yard range. Maybe further. 

Louis has a good point as to catching bullets at speed. Thinking tests for nose slump and amount of upset. Place recovered bullets in the lathe to test for nose run out. 

This is serious business, Jack. Straighten up and fly right. Remember, I am your spotter.

     Joe. 

        

My private range is within sight of the base and can here the seals. Pretty sure they know who and what I am. Can hear um now, there goes that Noodlehead with his blunderbuss.
Sailing close the the dry dock keeps them on there toes too. Just as you see the bow of the chase boats go up, TACK!  

     Joe. 

I just googled "sweeping compounds".  There are many different types, but my bet is that was what Dr. Mann used.  

As a kid, I was the clean-up boy in a large commercial building.  The boss had sweeping compound in big barrels, maybe 30 gallon size, maybe 4 to a pallet.  IIRC, it was colored oiled sawdust or maybe shredded wood.  The individual grains were much heavier than paper, but lighter than sand.

I would build a box 30" wide, about 30" deep and about 8 feet long. Only cover the bottom, sides & back end. Put target paper over the open front end and pack it with sweeping compound about 2 feet deep. Put a tarp over the box when you shoot, that will keep the sawdust inside. 

Shoot so that the bullet enters the long axis of the box, right in the middle of the sweeping compound.  Getting set up for the tests would probably cost $250 to $300 for everything.  With some experience, you could make the box shorter than 8 feet.

I built such a box & filled it with sand (dug from a sandbar in a river, but screened to get rid of the gravel) to test penetration & deformation of jacketed bullets from .470 NE, etc., fired from rest & over chronograph, range about 50 feet.  I learned a lot, but the sand scratched up the surface of the bullets.  Greatest penetration was about 4 feet.  Bullets might go a lot further in sawdust.

JS47 wrote on Feb 25^th, 2014 at 10:13pm:

I know a neighborhood 'kid' (now 50+) who has the scars on both hands and his scalp who does? Thankfully it was a light arrow ...

JS47 wrote on Feb 25^th, 2014 at 10:13pm:


Not only arrows, but a 4-1/2" mortar firing a 7.5 Lb round.  Went up about a hundred yards.  Not too bad to figure out where it would land - 10 to 12 SECOND time of flight.

(Don't try this at home.)