Using old green Knight sabots and 240 gr XTP's from an H&R Huntsman.
Accuracy has been abysmal (all over and sometimes not even touching a 2'x3' target at 100yards), and during my walks to and from the target, I have recovered the sabots, some pieces, missing petals, twisted up and mangled.
I'm assuming that this and the accuracy issues are hand in hand.
I'm working up a new load with Triple 7. Am I pushing it too hard? Does this cause the sabot damage?
You are probably having a couple issues. First, you are probably experiencing the dreaded Triple Se7en 'crud ring'. This is a crusty ring right where the powder and bullet/sabot meet. To best combat the crud, you need to swab the bore clean between every shot, or you will never get any accuracy. This also causes the sabot problems.
Secondly, you could be experiencing problems with barrel heat. This will also be compounded with the 'crud ring'. You can combat this by swabbing the bore clean between shots, and giving it time to cool.
The old Knight sabots are not the best option in any of my 3 H&R/NEF Huntsmans and Sidekicks. The Harvester Crush Rib works much better in my rifles.
Another tip I would give you is the 300 gr bullets are generally much better shooters thatn the lighter ones, but your issue is likely one or both of the above.
My Huntsman is my favorite, and shoots just about everything out there. Visit the H&R/NEF Huntsman/Sidekick Forum for several range reports, and good bullet/sabot options