Conveyor belt rubber backstop.

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Conveyor belt rubber backstop.

Post by bladeracer » 27 Aug 2017, 6:18 pm

I bought ten sheets of used 12mm rubber belt this week, cut to 900mmx1800mm ($270).
The plan is to hang them inside a steel box with a 40mm gap between them to allow bullets to fall into a tray at the bottom for recovery. The idea being that there will always be an undamaged sheet that will bounce the bullets off with no penetration. I'll probably make the back of the box out of 5mm mild steel just in case anything manages to make it through all ten sheets of rubber.

I stood four sheets up with 40mm gluts between them for some testing using CCI 40gn SV .22LR.
The CCI SV at the muzzle has 104ft/lbs energy and is entering the first sheet at 1080fps, and exiting at 735fps. At one-meter the bullets went through the first sheet, embedding themselves in the second, no bulge on the back but they're going to be hell to dig out of there. Two of the ten were sticking out of the surface and recoverable but the others were just below the surface. I'm guessing that means it takes 345fps of "energy" to pass through the 12mm sheet? Entering the second sheet, the bullet has enlarged from 0.223" to 0.34" so I expect it would burn up a lot more velocity trying to penetrate the second sheet.

At 25m they went through the first sheet and into the surface of the second sheet, mushroomed to 0.35". A couple were sticking out making for easy recovery, the rest are visible but not accessible. At 25m it has 91ft/lb of energy and 1020fps.
At 50m they went through the first and collected in a neat little pile at the bottom - perfect! At 50m it has 82ft/lbs and 960fps.
The bullets are very deformed, almost spherical and mushroomed to 0.34". At 50m the bullet is probably exiting at around 600fps or less, and bouncing off the next sheet. So I guess that tells me that the deformed 0.34" bullet needs at least 600fps to be able to penetrate the rubber at all? Surprisingly, they are not tumbling. I might try to find out what distance will stop the bullet from even entering the first sheet as that should tell me the minimum energy required for the bullet to actually penetrate the rubber. The CCI SV should be doing about 600fps by about 400m, so it'll be an excuse for some long-range .22LR shooting :-)

Two sheets of 12mm rubber makes for a very portable backstop, so I'm thinking now of building one just for .22LR and one for everything else. For 50m .22LR it would only need to be maybe 600mm square. I haven't weighed them yet, but near as I can determine they should be around 14kg/m2 (these have no steel wire in them). Two 600mm squares are only 10kg of rubber. The full ten-sheet, 900x1800mm target is closer to 230kg of rubber, plus the structure to support it, so it'll have wheels and a draw bar on it.

I then stood up all ten sheets and fired two 173gn SP at it from the 7.62x54R. I haven't chroned these but I estimate they're in the 2400-2500fps range. From about one-meter range they plowed through seven sheets of rubber and bounced off the eighth sheet, both of them mushroomed to 0.61” diameter.

Don't suppose anybody else has tried something similar?
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Re: Conveyor belt rubber backstop.

Post by Cooper » 28 Aug 2017, 12:48 pm

I have some off cuts of Linatex target backing. It the fancy 'self heal' type rubber. Might make up a 22lr target and see how it performs.
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Re: Conveyor belt rubber backstop.

Post by bladeracer » 28 Aug 2017, 4:22 pm

Cooper wrote:I have some off cuts of Linatex target backing. It the fancy 'self heal' type rubber. Might make up a 22lr target and see how it performs.


How thick is the material?
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Re: Conveyor belt rubber backstop.

Post by Gwion » 28 Aug 2017, 6:32 pm

Sounds like a great idea but 250+kg is damn heavy!!!
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Re: Conveyor belt rubber backstop.

Post by Cooper » 28 Aug 2017, 6:42 pm

It's 6mm thick. I only have a couple small off cut rolls. I might be able get some more. I'll shoot some this weekend and see how it performs.
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Re: Conveyor belt rubber backstop.

Post by bladeracer » 28 Aug 2017, 10:43 pm

Gwion wrote:Sounds like a great idea but 250+kg is damn heavy!!!


But lighter than the dam I normally shoot at :-)
The primary reason for doing this is bullet recovery, I'm sick of having to dig them out of the dirt with the metal detector. Hopefully this will allow me to simply empty the tray when I want to cast some more bullets.

It'll basically be mounted on a trailer and towed into position as and where needed.
I had originally intended to make it 900mm square, but I figured that was going to be too heavy to be easily portable anyway, so I might as well just make it bigger. It'll be inside a steel cabinet with doors and storage for targets, patches and such, protected from wind and rain. And big enough to put up 24 A4 targets at a time.
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Re: Conveyor belt rubber backstop.

Post by Gwion » 29 Aug 2017, 8:32 am

Definitely like the idea because it will get my wife off my back about "filling the hillside with lead". Where do you get the rubber? Thinking i might try to knock one up for 22lr when i find a few spare bucks.
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Re: Conveyor belt rubber backstop.

Post by bladeracer » 29 Aug 2017, 1:46 pm

Gwion wrote:Definitely like the idea because it will get my wife off my back about "filling the hillside with lead". Where do you get the rubber? Thinking i might try to knock one up for 22lr when i find a few spare bucks.


I live very close to several coal mines (being in Gippsland).
I rang Belle Bann, they cut them to size for me and I went in and picked them up.
There are places that will ship it but it can be expensive.
Quarries and mines go through mega tons of the stuff.
If you can't find any let me know and I'll ask the guy here about sending some to you. I'm going to be grabbing some 600x600mm pieces myself anyway to make a rimfire one.
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Re: Conveyor belt rubber backstop.

Post by Blackened » 29 Aug 2017, 3:22 pm

Never tried anything like it, certainly keen to see some pictures of the end result if you make it happen though.
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