I Need a Better Backstop

[DHunter]

Related, I just happened to run across this short video:

After the part about the bullet-proof vest, they shoot through boxes of sand to see how far the .50 PB round would get.  Not very far.

[MJP]

It's because of the speed, the bullet gets fragmented.
We measured around 1.5 meters of penetration in to sand back stop with the 20mm, normal rilfe rounds penetrate only some 10-20cm in to the same sand berm.

Energy at the muzzle is just about the same.

Marko

[TPL]

20mm energy is close to 9.3 x 62 large game rifle round but if we look at the momentum, 20mm is about three times that of 9.3. And yes, bullet stays in one piece.

It is slow but hard to stop.

Though, we haven't see the bullet, should have an excavator to dig it up. 

[Gut2Fish]

A note on wetted sand. It varies by sand composition and some sands max out around 13% water by weight before saturating. If you kept it 8% you shouldn't have pooling of water ever. Sands low in fines/dust saturate 7-8%. Oil is 0.8 the weight of water so should be used in equivalent volume.

50 lbs of dry sand will take 2 quarts of water, close enough for 8% moisture, or 2 quarts of oil for equivalent volume.

25Kg to 2 liter.

[Smoketown]

Something to keep in mind ...

Silicosis and sand ...

I'll take "heavy metals" over sand any day ...

But, that's just me ... YMMV.   

Cheers,
Smoketown

[triggertreat]

I think I'm going to go with a long/wide tote that has fairly flat ends with a decent lid latch filled with rubber mulch.  It should be at a minimum 29" long or longer from shooting end to shooting end.  I plan on screwing in a fitted board to allow a space internally on at least one end if not both so the mulch falling out of the shot board holes will just drop down into the gapped space and not on the floor.  A gap big enough that I can duct tape the holes from the outside of it periodically.  I am planning on keeping the shot holes at centerline as much as possible and up from the bottom a good bit so this plan works out best.

I do have some steel plates too, but I'll have to make a decision as to whether I'm only shooting at one end of the tote or both.  I guess if the tote is long enough, I could place the plates in the middle/center of the mulch.  I'd rather have the option of shooting either end for less maintenance.


The whole idea is to stop a 300 FPE slug with fairly tight groups from a rest about 12 feet away indoors.  Some testing will be done outdoors at near PBR to be sure this works well prior to indoor use.


P.S.  If I can find a tote that fits inside the outer one well enough for gapped space on each end, then I can just move the steel plate from one end to the other easily, which gives me the option of shooting either end of the tote and also less build time.

[subscriber]

Something to keep in mind ...

Silicosis and sand ...

That is another reason why an indoor sand trap should be "damp".  To keep the dust formation down.  Outdoors, this would be less of a problem; unless you stay close to the backstop and have a breeze blowing at you.

Damp with water indoors = mold.  So, no to water.  Used engine oil probably has a bunch of nasty stuff in it too that will offgas over time.  Cheapest unused oil would be much better.

Most roads point back to rubber mulch...

[DHunter]

Damp with water indoors = mold.  So, no to water.

It shouldn't be a problem.  We've had an indoor aquarium with the top open for 25 years and definitely don't have any trouble with mold.

[Kinetic45^]

I should mention that with my tub, turned on it's side, where I shoot through the removable lid (which is screwed down to stay down) the 'thickness' is 15 inches.
With my 45 Texan with a TalonTunes bottle filled to 3600 on a regulator'and mounted in a rifle vise where every shot hits exactly the same point and shooting over 45 shots chronying various bullets from 220 gr to 440 gr no bullet penetrated.  I used to have a 1/4 steel plate I put in the bottom of the tote before I filled with mulch but no bullet, of any power, reached it when I emptied it to check.  I guess you could keep one in for peace of mind or have one behind it separatly.  Stuff falling out became almost a non-problem when I started using the sheet of rubber in front of the mulch until the hole gets quite large and as you change targets or just every so often apply some tape.

Note that every so often it helps to flip the tub back on it's bottom to shake the mulch up and resettle it to collapse any cavities that have formed... Like 70 or 80 shots of big bore. If you were shooting through the side (?) I guess you could just 'rock it back n forth' hard a couple of times to do the same thing.

I used a huge tub at first that filled with mulch was too heavy to move but changed to this smaller one that although it is heavy I can pick up and walk with. It's 20 x 16 and 15 inch deep mulch

So it's a couple of hours later and meanwhile I went out and emptied the mulch from the tub an inch at a time to see the depth and record them.  The tub had been emptied last month so this is just a few sessions of shooting.  Also, I put the tub on a scale first and it weighed 141 pounds with the slugs in it.

First I came to pellets of .22 and.25 shot from a Chief and a Marauder and 90% were in the 2 to 3" zone
then I got down to the 5 - 6" depth and you can see what I recovered by the picture labels
there were a couple of bullet going down but deeper scattered in but most of these were around 8" then it thinned out again
Until I got to about 9 to 10" deep and encountered another 'layer'
I found nothing else until I got to the 14 inch deep and found the solid .457, 362gr launched at 4500 PSI out of my Texan at point blank and over 900 FPS

You can see that the different depth probably correspond to the FPE of the slug.
It is true that the last slugs (457) were just an inch from penetrating but really they are a special circumstance and if I was shooting these a lot I would put the steel plate back in the bottom of the tub.  But since MOST of the .357 and .457 had stopped earlier and had a lot of mulch left to travel through I feel safe for regular pellet rifles and regular big bores.  There are several .457 I recovered in the 8 to 9" layer that were shot at 3000 PSI with a regular valve, not the Doug Noble high pressure one that drove the others so deep.  I also note that although you can see some bullets that struck other bullets  they tended to spread out in a 'pancake' of about 5" even though they all were shot into the same 1 inch on the face of the tub so I plan to never shoot closer than 6" from the side to prevent a bullet from veering and punching out the side.  It would still hit the wall right beside the tub but I still don't want that, haha.  to see a larger picture of my rifle vise, chrony and backstop I have one at  https://www.gatewaytoairguns.org/GTA/index.php?topic=152105.0  , post #18

[triggertreat]

Thanks Carl that helps a lot! I would like to keep the weight down and not go overboard there.

[AP2020]

I have approximately 2 feet thick of rubber conveyor material backed by a 1/2" thick AR500 steel plate. I have shot my 45-70 Gov't into the backstop in my basement!

Most powder burning projectiles penetrate less than 6". I rotate the conveyor material every month.

[subscriber]

I can imagine some lower powered airgun projectiles bouncing off solid conveyor belt, returning to sender.  Also, the belt will become "holy" when hit multiples times in the same location.  The beauty of rubber mulch is that it has almost no bulk strength, and so collapses in on holes punched by projectiles.
 
In any event, rubber acts like a super viscous fluid that is extremely "lossy" to projectiles.  Its particular combination of mass and stickiness seems to work very well.  This, while rubber is much less dense than the projectiles, so screening out the lead later is easy. 

[HunterWhite]

Bob, your original design looks pretty useful.  You have built it so that you can replace the sacrificial wood.
If you have a slot on the left and right sides then you could cut the plywood longer than the trap. Even the full width of the plywood,  in the USA it's 48 inches (about 1,2 meters).
Then periodically slide the sacrificial plywood left or right.
If you place the bullseye a few inches above the center then you can flip the sacrificial plywood over and run it back through.

When it has a lot of holes then just make a trellis for garden vines.

[PakProtector]

My outside  traps are a foot by a foot mouth, with the top plate angled 30-degres downwards. They rest on a bin of sand. Dry. the wet stuff can hold a hole, and that is not so good. The plate is 12 ga/.106" mild steel. They are not for indoor use, as there is a lot of splash, and a wee bit of dust as the mostly spent lead hits the sand.

Inspiration taken from reading about the sloped armor on Panthers...
cheers,
Douglas

[Kinetic45^]

Angled metal deflectors have their place (had multiple ones) but are usually not backyard friendly...
Most of us do so much to have a quiet gun but the CLANG of pellets or especially slugs hitting that backstop gong sure alerts the neighbors SOMETHING is going on!
That's why I switched to soft targets.

[triggertreat]

I finished my indoor backstop project today.  I repurposed two heavy duty Brute totes that I used for raising worms.  They are 15" deep and one is stuffed to the rim with shredded rubber mulch.  Boy is it heavy at around 125lbs, guessing.  That's four 0.8cf bags of shredded rubber mulch in there.





On the second tote/bid, I hot glued a 1/4" steel plate into the bottom, and the rubber filled tote can slide in and out of it to reduce weight when moving if need be.





I packed the mulch in using a sledge hammer and then secured the lid with screws.  I also marked where the steel plate lines up, and where the actual bottom aligns due to there being a narrower bottom than the top portion.  Now I know where best to put the target to align with the steel plates, and not shoot out the slanted sides/ends.





I also repurposed an old table saw stand that has wheels on it so I can slide this contraption in place for gun tuning and shooting, and then out the way in the tight quarters of my man hut.





The final setup looks good to me and is ready for any kind of shooting and tuning I want to do this winter.  The hut is heated with a propane heater.  The shooting angle is also aligned with a large cedar tree trunk if all else fails.





I have no plans of hauling this heavy contraption out to my 50 yard range due to its weight, but do have a dolly, so maybe to capture the lead for future cast.  My immediate plan is to move a few of these cut logs I have nearby in place for the 50 yard range backstop.





 

[Tater]

Great set up there Keith.

[triggertreat]

Great set up there Keith.

Thanks Jerry!  Nothing special, but hopefully it will stop the Slayer.  I had to work the garden today before the approaching hard freeze.  I'll be testing it out soon to see if it will.

[FuzzyGrub]

Looks great, Keith.  That should do the trick.

I was lucky enough to have an old wood stove to repurpose as a basement pellet trap.  But, even with that, I added a 45 degree barrier of old cast iron window weights.  Plus allot of "stuffing" to keep the noise down.  Someday, I need to do the separation to reclaim the lead.  It's not very portable, though.   

[triggertreat]

Looks great, Keith.  That should do the trick.

I was lucky enough to have an old wood stove to repurpose as a basement pellet trap.  But, even with that, I added a 45 degree barrier of old cast iron window weights.  Plus allot of "stuffing" to keep the noise down.  Someday, I need to do the separation to reclaim the lead.  It's not very portable, though. 

Thanks John!  I did have a smaller box of shredded rubber mulch I have been using.  I put that mulch in one of the new mulch bags to sort the lead out of it later.  I did try to sift the lead some and only got one tin full so far, but it was a tedious task for sure.  The old mulch turned into much smaller pieces, many smaller than the pellets, but not all of it.  I also had rolled up cloth mixed in there, that was a mistake as it got shredded within the mulch.  Wished lead was magnetic, LOL.  At least as far as being able to sort it from the rubber that is.