Wesley, Howa / Legacy Sports Customer Service should be able to put this to rest for you at : 1-800-553-4229 or by online inquiry here : howausa.com/contact-1/

Wesley, I'm looking and looking and it's the only difference I can find also. They both have a 24 inch threaded barrel with 5/8×24 thread pitch, both have green/black stock, both have a 1:8 twist rate, only difference is one holds 3+1, one holds 4+1. If they are similar enough none of use can find a difference id buy the cheaper one and call it a day. Hope this helps.

Wesley, The only difference I can find listed is the OAL is 44.75" for HHS45533 vs 43.5" for HHS75533 (and 3+1 vs 4+1). Jon