Make sure that u wrap your hands properly. Make sure that u learn/learned a good wrapping technique from someone who knows what they're talking about.

What kind of gloves are u using?

I would suggest 16-20 oz. super bag gloves.

Punch with proper form.

I see that u said you're hitting a 70 lb. bag. Is it canvas? Is it very hard?

The reason I ask is, I've seen people hit bags that have been wet and then dry out. They tend to get very hard. And I would never recommend the little old school bag gloves to any one that can bang. (That's just my opinion, as I had had many hand injuries).

Do these things correctly and there is no reason why u can't let'em rip.