Sharing a couple other thoughts discussed with Lehigh. One of my main concerns with the SP bullet is - at what velocity will the bullet CF function
stop functioning. According to the Lehigh specs the SP bullet operates from 3200 fps to 1200 fps which at extend ranges could be a problem. My calculated ballistic sheets show that I really should be alright to 200 yards.
Addressing that problem in our discussion is when he brought up the Subsonic LP version of the bullet. This bullet operates from 2500 fps to 750 fps - so it would certainly would operate out the the 200 yard mark.
Another topic brought up in our conversation was
bullet slippage in a sabot. Since the Lehigh brass bullet is so hard and smooth the possibility of it slipping certainly exists. Which brings up another couple of points... This bullet is designed as a centerfire bullet and is manufactured to much tighter dimension specifications. Especially the diameter specs. Because of this I have found that shooting a comparable Lehigh .458x305CF in a normal MMP HPH .457/.458x50 sabot it really seems to go down the bore very smoothly but in my mind somewhat loose which might allow the bullet slippage in the sabot. Because of this concern I started using the MMP Black .452x50 sabot - which did increase the amount of pressure needed to load the bullet, and I feel reduce the fear of bullet slippage.
This picture tends to show what I am indicating
Look closely at the bottom of the bullet in each sabot. The far left is a Lehigh .458 muzzle loading bullet installed in the Orange sabot. Notice the bullet is not completely seated in the bottom of the sabot. In the middle picture the SP bullet drops very right into the sabot and seats all the way down. Almost loose in the sabot. It is just a more skinny load. The left had pic is the SP installed in the Black HPH-24 sabot and as with the ML bullet it is not seated in/on the bottom of the sabot. The bullet will completely seat when pushed through the crown and down the bore.
With this tighter fit the chances of the bullet slipping in the sabot is reduced.