Way too much scope for service rifle. You'll have major problems finding your target on certain matches, even with it dialed all the way down to 8x (match 4 comes to mind, among others).
If you've got your heart set on high magnification than I'd probably go with a 3-9x but it isn't neccessary. In my (limited) experience, the guys with the fancy space guns don't do any better than the guys who (like me) use the 3.4x Elcan on their issued rifles. Their scores might be a little better at the 500m mound but the military guys will still beat them overall.
I still don't understand why this scope won't fit. Are you trying to mount this on a carbine gas system? Definately overkill!! Get yourself a low power variable scope like 1-4x or 1.5-5x. Just my 2cts. Your money is better spent on ammo and trigger time.