I'm a little confused with your post, you say you have a classic trap with a 21" barrel? Usually trap guns have 30' barrels and sometimes higher ribs, also if it has a trap stock they are designed to make the gun shot high. Trap guns are designed so you can keep the bird above the barrel and break the target as it rises. It also matters what type of hunting you will be doing with it, does the 21" barrel have screw in chokes? If it does it would be fine for upland hunting or turkey hunting. You can find used barrels on many of the gun sites. You may want to purchase another stock that is flatter for hunting, good luck.