Tuning Texan .457 mod

As far as accuracy goes. I noticed that I can grip the handle as tight or loose I want but stay easy on the rest of the rifle hold and all shots are clover leaf I don't own a range finder but using a 300 foot tree fallers tape I estimate I shoot from 50 yards to around 1200 yards. My excellent eye sight and steady nerves plays a part. I think any one can duplicate results with any texan off the shelf. 
 
Also another experiment was with factory spring. I fired a 166 grain slug a 340 and a 400 grain slug into the side of a rust free 10 inch culvert at 20 yards. The 340 slug went threw one side and left a good size dent with sings of cracking on the other the 166 grain went threw one side and tore threw the other and the 400 grain went threw both sides with no sing of stopping and penetrated solid earth. 
 
I have my open sights set at 150. But I know my land and know the clicks on the scope and the adjustment on the open sights. For any point on land. Out here there is turkey coyotes deer bear and mountain lions that grab up sleeping ridge backs trained to keep bears out of the home. Ha ha lol. I love it and so even with air guns it's extreme in my territory.