movement types and effects on moving average cost

Hi all,

can anybody explain me what is moviment type n° 309 (transaction mb1b).

Before of this movement I had in the storage a stock of 15.000 KG and a moving average cost of 6,70 u20AC.

Then I did a movement 309 in MB1B for 4.050 kg.

After that I did a movement 261 (probably with transaction qa11) for 11850,300.

After these movements my moving average cost decreased to 1,29.

what kind of movement are 309 and 261?

Can they change my moving average cost?

thank you

C.