Mamoswine's Special Attack ranges from 130 - 262, so Blizzard is not needed. Blizzard also has low accuracy, and won't do much. I'd go with a different set with Ice Shard, which is more useful, and has more PP.
Try this set:
Mamoswine (M) @ Life Orb
Trait: Thick Fat
Nature: (+ Atk, - Sp. Atk)
EVs: 252 Atk/ 252 HP/ 4 Speed
- Ice Shard (STAB, advantage of low speed)
- Earthquake (Strong, STAB)
- Curse (Even further attack)
- Stone Edge (Strong)
This set maximizes attack as much as possible.