hehe, 3 things (I have had them all happen to me with loose powder)

1: if you prime the rifle aimed to the ground. you could loose your charge. and just hear the pop of the primer.

2:if you load the gun (loose powder) and pack it. a very loud bang and a lot of smoke.

3:if you load the gun and not pack it. fizzles lots of smoke. very dirty barrel.

have not done that with pellets. only shot 12 pellets loads.