OK, this glitch is a way to get 250-255 of a weapon. However, make sure you follow my directions EXACTLY how I say to, or else the trick will not work.
To start the trick, you need the Avenger sword, which you can find in the Sylvan cave in the underground, I think.
First, equip Cecil with arrows in his GOOD hand, and the any kind of bow in his BAD. Get into a battle (preferably an easy one), and make sure that nobody does anything. If a character's turn comes before his, have them parry (press right and the parry option will come up). Once it gets to Cecil's turn, enter the item screen. Grab the arrows he has equiped and bring them down to an empty slot. Without leaving the window, select the Avenger sword and move it up to his BAD hand.
From there, press B to exit the items window and his commands will disappear because the Avenger sword causes the person with it equiped to be berserked. Don't have any other characters do ANYTHING! Just let Cecil beat up all the enemies.
After the battle, go to the Equip screen for Cecil. Move the Avenger sword to an empty slot, and then without leaving the screen move the sword you would like to duplicate 250 times into his GOOD hand (the one with the numbers). De-equip, and re-equip, and voila! You should have a sword with a circle and a number next to it in your inventory. If not, make sure you followed my directions EXACTLY.
This works well for duplicating the excalibur, and having Edge throw it for massive damage. Happy gaming!