I feel like "a little small" is actually a good thing, as IG weapons always look awkwardly gigantic to me to begin with. A size reduction would actually make things look more sane and believable.
That said, if gigantic is what you want, go for the CAD gun range in Hasslefree's catalog rather than their regular guns. The CAD gun masters were purchased by HF from another company rather than being made in house like the pulse rifles and rail guns and such, and are in a larger, more GW sized scale.