Those old shells will have 1 of 2 types of fuzes. One is a wooden tube, the top of which may be sealed with wax. The wax should be removed with an emery board or sandpaper. That will expose the powder in the fuze. You then put the shell into the water, fuze-side down, for about a week. The powder inside, by that time, will be a watery mush & completely safe. You can then pull the fuze & note that it has markings along it. Each marking stands for 1 second. You literally 'cut' the fuze with a saw to burn the proper length of time.
The second variety has a lead top with a raised spiral on it. The spiral is marked with numbers. Each number stands for 1 second. To 'cut' that sort of fuze there was a brass or bronze tool with a V-notched head. You placed the tool at the proper timing mark & hit it with a wooden mallet. If the fuze has not been cut, simply erode it with sandpaper or use a brass or bronze pointed instrument to open the powder trail. Submerge it in water for a week & it's perfectly safe.
There were no 'impact' fuzes for field artillery before the 1890s. For anti-personnel rounds the guns were loaded with canister, grapeshot, or langrage. Canister was large musket balls inside a container which had a fiber top. When the gun was fired the canister held the charge of balls together for about 300 yards, then fell away. At that point the balls began to spread. Grapeshot had a wooden sabot at the bottom with a dowel set in it. A woolen bag was fastened to the sabot, as was a heavy cordage net. The bag was filled with musket balls. The net kept the balls from exceeding the bore diameter of the weapon. The bag and net were tied at the top. When the weapon fired the sabot pushed the load out of the muzzle, the bag & net burned away, & the charge began to spread. Langrage was whatever you had handy--horseshoe nails, broken pottery, short pieces of chain, what have you. This stuff was usually used in a short-barreled gun--a howitzer, normally, though at the Alamo they actually had a carronade, a shipboard gun designed to sweep the enemy's decks. You pointed the langrage-loaded gun at the fort's gates & when the gate came open you touched it off. The result was devastation.
Modern shells have 4 sorts of fuzes--mechanical time superquick or MTSQ, point-detonating or PD, concrete-piercing or CP, & variable time or VT. MTSQ fuzes are set with a special fuze wrench before inserting into the projectile. They can be set anywhere from 1/10 sec to 70 secs. MTSQ fuzes will also detonate on contact with any solid object. Killer Jr., used in Nam, was an MTSQ fuze cut to 1/10 sec & fired with a charge 7 load. It would get about 400 meters in front of the muzzle & detonate. It was a good idea to be buttoned up in the gun when you fired Killer Jr. It & what was called 'Krispy Kritters' were used to repel mass attacks, "Krrispy Kritters' was charge 7, no projectile. When you pulled the string on a 155 you got about 500 meters of 4500-degree flame, 50 or so meters wide, which was why it was called 'Krispy Kritters.'
PD fuzes detonate on contact with any solid object or can be set with a 1/5 sec delay to penetrate into the ground. CP fuzes are a delay fuze with a very hard nose. The momentum of the projectile carries it into a concrete fortification. The hardend nose allows successful penetration without detonation until the projectile has penetrated the concrete.
VT fuzes contain a radio transmitter & receiver. When the signal from the transmitter is received at a frequency which indicates the projectile is 20 meters above the ground, the fuze detonates the round. However, VT fuzes are subject to several things. Fired over water, they will often detonate 40 to 50 meters up. In addition, it's not a good idea to use them in heavy fog, because the fog will reflect the radio signal. Older--WW II vintage--VT fuzes could be set off simply by the radio signal hitting a large bird.
Field Artillery doesn't use shaped-charge projectiles. Those are used with tank rounds or with specific anti-tank weapons like the LAW or light anti-tank weapon.
Nobody other than qualified EOD personnel should ever attempt to defuze or handle in any way any modern explosive projectile. Duds are particularly dangerous. If an MTSQ fuze failed it may have failed because the timer got stuck--say, 1/10 sec before detonation. Disturbing it, even accidentally, could cause that timer to tick off that last 1/10 sec. At that point whoever disturbed the round will have to be scraped off the trees & rocks--if they can find enough of the guy to scrape off.
