You may consider trying some of the 45-70 rifle bullets and use the orange mmp sabot to go along with it. Many of these bullets were designed to expand at the lower trapdoor velocities and can be bought pretty cheaply in bulk. I believe the sierra pro-hunter 300 grain bullet I used last season was designed to expand down to 1200 fps. For short range shots you should probably have enough velocity for the bullet to expand well.