Can I use Horus Heresy models for my 40k Ultramarine army? : r/Warhammer40k

The Horus Heresy – Legion Overview – The Ultramarines

Fafnir Rann Horus Heresy Rules Unveiled by GW

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Ultramarine test model. Still need to paint the base. : r/Warhammer30k

MASSIVE VOODOO: FM: Horus Heresy 30k Ultramarine Captian

10th Edition Competitive Faction Focus: Space Marines

Warhammer 40K Horus Heresy Space Marine Chaos TARTAROS TERMINATOR Bit Bits sons

And These Are My First Warhammer 40K Models! C&C Welcome, 60% OFF

My son wants an iron warriors army to fight against my black templars. should I use the 40k chaos marines to build them or should I use horus heresy models to build