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What happens when you shoot Pykrete?

pykrete before shooting pykrete after shooting
Pykrete Before Pykrete After

What happens when you shoot ice?

ice before shooting ice after shooting
Ice Before Ice After
Photos and shooting by J Gordon Holley July 22, 2000.  Both the pykrete and ice were frozen in 1 gallon milk jugs for one week.  The pykrete was 10% sawdust by weight.

Both were shot with a .243 rifle at 100 meters.  A .243 bullet fired from 300 meters can push a 1 lb object for a distance of 1000 feet.  Remington Catalog lists stats for a .243 bullet:

243 - 100 gr bullet 1,945 ft - lbs energy .30-06 - 150 gr bullet 2,820 ft - lbs energy .300 Win mag 150 gr bullet 3,605 ft - lbs energy


For those of you interested in how Grippy and Cormo come up with the stuff in their science theater projects -- here follows their research so far on pykrete.

During WWII Pykrete was going to be our secret weapon -- boats made of ice and sawdust that don't melt and don't sink. According to Eccentrics by Henry and Melissa Billings, Geoffrey Pyke invented pykrete (sawdust ice) in the early 1940's as our secret weapon in WWII -- boats that can't sink. It was never used because the war went nuclear, but 60 foot long boats made of this stuff were floated on Canadian lakes during the summer of 1943 and did not appreciably melt.

To make pykrete I needed to get sawdust. Called 3 lumber yards. The 3rd said to call back the next day. Then they said to call about 4 pm and they'd let me know. At 4 pm they said they had one bagful. I went with one bag. I could have brought 5. But now I'm making pykrete.

Eccentrics said the pykrete was 14% sawdust. It didn't say by weight or by volume. I'm making pykrete in milk and orange juice cartons. They hold 64 ounces, so 9 ounces of sawdust is about 14% by weight. I weighed the carton -- 2 ounces -- and set the balance to 11 ounces. I had to keep mashing down the sawdust to get the balance up to 11 ounces. Then I added water. There was room for 7 cups in addition to the sawdust. I also made a control of plain ice water.

This size block of ice does not freeze quickly. I started one set on Wednesday Sept 25. On Friday, there were still bubbles in the control ice that moved when I shifted the carton. The carton of pykrete has split on one corner. It must expand differently from the regular ice, which is growing taller as it freezes.

Today, September 28, Saturday, I started another two cartons -- one pykrete and one control. We used an orange juice carton I saw when I was walking home by the used book store -- Eric picked it up on his morning run. We washed it with dish soap, rinsed it, and cut off the top.


weight with carton (2 oz): 

with sawdust 3 lbs 14 oz.

without sawdust 3 lbs 11 oz.

placed into tub of water outside -- water is 23C at 1:20 PM

at 2:08 PM water is 19C and control ice is completely melted. Ice lasted 48 minutes Pykrete is shedding sawdust, but is intact -- approximately original size. It is soft to touch and bits of sawdust brush off if I rub my hand on it. .

5:38 PM, pykrete completely melted. Water temp 21C. About 4:30 PM, I found the pykrete sunk to the bottom of the tub (approx 8 gallons of water). I reached in and shook it -- lots of soggy sawdust fell to the bottom of the tub. Then the pykrete floated again. Pykrete lasted 3 hrs and 18 minutes.

Pykrete update. 10/05/96

I placed the ice on the grass in our yard and dropped a 5 lb free weight crossways on it from 2 feet elevation. It chipped. Same for the 10 lb weight from 2 feet. Severe chipping at 15 lbs dropped crossways from 2 feet. Then tried dropping end - down. 10 lbs dropped end-on from 3 feet shattered the block of ice --- this is a half-gallon milk carton or loaf of bread sized ice block.

Next, repeated the above with the pykrete. The pykrete barely dented with the weights dropped crossways on it from 2 feet. Again, dropping the 10 and 15 and 20 lb weights from 3 feet end-on barely dented it. Then Steve, a visitor, dropped the 20 lb weight end-on from 5.5 feet and the ice sheared -- a flat horizontal break, about 1" below the top surface. The top sheet broke into two pieces at the point of impact.

Additional experiment. I took approximately equal sized chunks of ice and pykrete and poured 2 ounces of boiling water over them. The ice pitted about 1/2 inch at the point of contact. The pykrete spread the hot water across the surface, a few bits of sawdust washed off the surface. I repeated the expt with another 2 ounces of boiling water. The pit in the plain ice deepened to over an inch. The pykrete again remained flat and a few more bits of sawdust washed off the surface.

This is the experiment that FDR did when he was first given a piece of pykrete. No wonder he was impressed!

Question: Which (pykrete or ice) will cool better and / or last longer in an arctic picnic cooler?

Experimental setup:

Freeze ice and pykrete in freezer compartment of refrigerator in gallon milk cartons. Place milk carton of frozen pykrete in a plastic bag to catch leaks. Measure room temperature with thermometer. Place bag and box and thermometer in cooler.

(note: the temperature of a typical refrigerator is 4C)

Data for Pykrete:

Room temp 10/19/1996 at 2 PM is 22C.

temp in cooler:

2 PM 22C

4 PM 11C

7 PM 12C

10:45 PM 11C


12:36 PM 12C

5 PM 11C (note I can poke a toothpick all the way into the sawdust. There is about 1" water in the bag around the box)

9 PM 13C (more water in bag)


8:47 AM 15C

2:24 PM 18C (this is room temp today)

duration of experiment: 2 days

Data for Ice:


room temperature 18C

Place ice into bag and then bagged ice and thermometer into arctic picnic bag at 3:50 PM.

3:50 PM 18C

6:35 PM 10C

9 PM 11C


8:45 AM 11C

10:05 AM 12C

2 PM 13C

8 PM 14C


7 AM 12C

8 AM 15C

2:20 PM 18C

room temperature is 18C

duration of experiment: 2 days


The arctic picnic bag is so well insulated that it negated any difference in the properties of ice and pykrete.


8 PM Placed a 1 cup baggie of Rubbermaid brand blue ice in freezer. Made up a baggie with 1 cup tap water and another with 1 cup sawdust plus enough water to saturate the sawdust (approx 7 ounces.)

Placed them in freezer.


8:30 AM Removed all 3 baggies and placed them on table top. Room temperature 18C.

Freezer is -16C. Note blue ice feels more dense than ice or pykrete.

10 AM visible melting in ice and in blue ice. Not in pykrete.

1:20 PM ice mostly melted. blue ice over 80% melted. Pykrete is soft about 3/4" around all edges.

2:45 PM Ice completely melted, and is room temperature touch(16C.) Pykrete soft all the way through, but feels cool to touch -- feels cooler than blue ice (13C.)


Again using the Arctic Picnic Cooler
1 quart Rubbermaid Blue Ice inserted at
9:30 AM Temp (18C.)
2:00 PM Temp (13C.)
8:47 AM Temp (16C.)
2:10 PM Temp (18C.)

1 quart pykrete in 1 quart freezer baggie inserted 2:11 PM temp (18C.)
7:20 PM temp (12C.)
8:50 AM temp (13C.)
3:50 PM temp (16C.)


Both blue ice and pykrete keep the cooler below room temperature for approximately 24 hours.
No signifigant difference in their usefulness for this purpose.


Placed 1 cup pykrete in a baggie and 1 cup Rubbermaid Blue Ice in a one-cup bag (as sold) on a sheet of plastic on my dining table, and stuck a thermometer under each of them. Recorded time / temp points follow:

Time Rubbermaid Blue Ice Pykrete
9:04 AM 22C 22C
9:07 AM -3C 0C
9:23 AM -2C 2C
10:20 AM 1C 2C
11:32 AM 1C 2C
1:49 PM 12C 3C
2:36 PM 18C 4C
3:39 PM 21C 13C
5:30 PM 22C 19C
6:25 PM 20C 20C

Conclusion: The blue ice remained usefully cold from 9:04 AM until approximately noon -- about 3 hours. The pykrete remained usefully cold from 9:04 AM until approximately 3:00 PM -- approximately 6 hours, or twice as long.

Note: Folded newspaper in a ziplock freezer bag, wet with just enough water to saturate the newspaper, and then frozen, is also effective.

Additional information about Pykrete:

brief bio of Pyke
more info on Pyke and Pykrete
the building of a Pykrete boat in 1943 on Patricia Lake, Jasper, Alberta, Canada
Pyke's vision for pykrete.
Another version of the history of Pykrete