I liked Longshot a lot, I have even taken to using it in other calibers like 9mm. I think it might be one of the most cost effective powders for 10mm.
I didn't get to 1300fps with max book LS loads (9,5gr) out of my stock barrel using 180gr Hornaday HAP's. I was running WLP primers, so maybe had I used dedicated magnum primers (like CCI 350), maybe I would have gotten there. IIRC my best averages were like 1260fps.
I could get to 1300fps but it was over the line some, no smiles or excess bulges out of the stock barrel.