I have found that they usually take in the region of 18-24 hours to soak up enough water to sink. When you are ready to shoot the pack, take it out of the water, pop it in a tub or plastic bag, and rush to the range as soon as possible. I have found that the books are still soggy enough to shoot with good results up to about half an hour after being removed from the water. Expected Results My experience shows that the results from a wetpack are extremely consistent. I usually fire at least three of the same bullets into the wetpack, and they always expand identically.
Penetration is also extremely similar.
Assuming that your dry paper thickness was about 20cm, you can expect almost all hollow point bullets to stop somewhere in the third book, sometimes in the second book. Some very heave jacketed hollow points like the 275 grain and heavier bullets will penetrate three books. If you are going to test these, make a bigger pack. Generally, as they do in humans, high velocity .357 Magnum and .44 Magnum loads break up, and often separate from their jackets. P loads for the .45 ACP also break up almost every time.