Take the nipple off and warm water-blast inside the muzzle over a sink - or outside using the garden hose & hose gun. You'll probably see crud coming out the nipple hole. If the ML has a cleanout screw nearby,remove that too. Both of these holes can also be cleaned using stiff pipe cleaners and Q-tips dipped in solvent.The nipple areashould be power-flushed after every use. FFF powderis better for lowering the odds of crud-buildup. It gets under the nipple easier& burns cleaner. I use it in calibers as large as 58.

Also buy a hotter nipple. Get Red Hots or Spitfires sold at Cabelas. Your size is the one markedItalian. Use hot #11 caps also. Buy RWS Dynamit Nobel 1075 Plus caps. They come in a red& green tin.