Mushroomed tips cause frequent miscues. They slide off the cue ball soon after impact, since there is no weight behind the leather to cushion the blow. Shots with english become especially difficult.
New tips tend to mushroom quickly. You can alleviate this problem somewhat by striking the balls extra gently, until the tip hardens a little.
1. Tip Pads
A relatively new weapon in the war against mushrooms, that some cue repairmen now provide, is a tiny pad placed between tip and ferrule when the tip is glued to the cue. The tip pad cushions the force of impact so well that the tip never loses its rounded shape.2. Mushroom Protector
A tip shaper, a.k.a. mushroom protector, is an accessory that keeps a tip round, available for about $8.00. To cool the friction produced, wet the tip's outside edge with slightly moistened fingers, then insert the cuestick at its tip into the shaper, resembling a thimble. Grind cue and shaper together with a circular motion. This squeezes the tip firmly into shape.3. Tip Tappers
Apply chalk to the tip in between shots to help it adhere to the cue ball. For a light yet consistent coat of chalk, one of two accessories called a tapper or "pricker" helps. Both lightly cut the leather, making small pockmarks that hold chalk well.A tapper is made of metal, with one side that is cross-hatched like a metal file. This surface slightly roughens and scores the tip. A few gentle taps, before starting play, does enough work to last for the session.
Strike the tip at an angle from above, preventing the tapper from hitting the tip's top head on, which flattens it away from the roundness desired.
4. Tip Prickers
A pricker has pointed spears of metal inside that jab the tip's surface, performing much the same function as a tip tapper. Place the pricker over the tip, then press down on the cue gently.A couple of licks from a tapper or pricker each time you play (either is available for several dollars), will not remove enough leather to shorten a tip's useful life. Enjoy!

