According to the Hornady specs, with the 240 XTP and 90 gr of black powder, you have 979 foot pounds at 100 yards, and 813 foot pounds at 150 yards.
Rest assured, with this proven deer killing slug, you have plenty of energy to make a clean kill on a deer at 150 yards.
The Hornady chart also shows that if the rifle is zeroed at 100 yards, it would be 1.6 inches high at 50, and 6.5 inches low at 150.
So, I would say, adjust your scope to make it 2 inches high at 100. Sighted in this way, you could hold dead on at 130 to 140 yards, and at 150 yards only need to elevate an inch or two.
As to what range you would be comfortable shooting at, this depends on how accurate a shooter you are. Re zero your scope to where you are 2 inches high at 100. Then, take a 3 shot group.
If you can make a 2 inch group at 100, that is good accuracy. This should give a 3 inch group at 150, good deer killing accuracy.
If you make a 4 inch group at 100, that is fair accuracy, and good enough for a 100 yard shot. But, this would open up to a 6 inch group at 150, not accurate enough for shooting at that range.
I tell you what I like to do. I get my rifle all sighted in. Then, I get a cardboard refrigerator box. I draw on that the silhouette of a deer. Doesn't have to be perfect, just get the body, the legs, and the neck. Cut your silhouette out with a knife. In the woods, you will be shooting at the silhouette of a deer, so this is great practice.
Go to the range, put that cardboard deer at 100 yards, and take one shot. Get your deer and go home and look at it.
All the Xs and red dots at the range are meaningless, in a way. All that matters is whether you can put that bullet into the lungs of a deer with one shot.
If you can kill the cardboard deer five time in a row at 100 you are good to go at that range.
Then, put him out at 150 yards and see how you do there.
You ought to buy a nice brass powder measure. You can find one for under ten bucks, I am sure. Very important to know what your powder charge is.
