Can I use .12 g bbs in my H&K G36c?

I just got a H&K G36c AEG. At the store they had 10,000 bbs .12grams on sale for $6 and my dad insisted I buy them, even though I knew .2 grams are better for airsoft. Now I was wondering will it ruin my gun using these as I am going indoor airsofting today and would like to know. If so I will try to buy some .2 grams from the pro shop at the indoor place. Thanks