For shooting, as in high power, a spotting scope is used more for reading mirage then spotting bullet holes.
Get one that picks up a lot of light, good and clear. As to power all you need is a 20-24 X. In high power I can see 22 cal (223) bullet holes at 300 yards.
Anything more powerful is going to pick up too much mirage and wash out the target.
The old army M-49 20X was dern near perfect for shooting.
When coaching for the AK NG Rifle team I had a 100 MM team scope. I came with 16-32 power. I used the 24X as it worked the best for seeing holes up to 300 yards, and judging mirage and bullet trace for long range. (you could even pick up the trace at 2 & 300 yards.
The biggest problem is people try for too much power. On our team scope I finely had to toss the other eye pieces because all my idiot shooters thought they needed the 32 X.
The same with scopes, don't go with too much power. Not only does it wash out the target (mirage) but it picks up heat from the barrel with interferes with you mirage. I've found 10-X to be perfect for me up to 1000 yards.
Also on a rifle you want a barrel ban, or a strap going the length of the barrel to break up heat waves coming off the barrel.
A hint for seeing bullet holes in "practice" targets" is to build your target frame so you can put another target about 3-4 inches behind your target. Reverse the target to the rear so its all white. When you look at the holes on your target (assuming they are in the black) you'll be able to see the white back ground of the second target.
If you have a dark back ground, such as trees 'n such, its almost impossible to see the holes regardless of the scope.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071