My daughter (a Bosun at HMCS York) shot NSCC at Connaught with me last year using a Colt Canada C8 running Hornady 62gr Steel Match. It shot like a house on fire out to 400m. At 500m, it got ugly. At 500 and farther out, you will be better served with a 20” barrel.
Back in 1993 the DCRA tried M Class, where you could shoot TR using a Service Rifle, which has since been folded in to the regular TR classes. I’m probably the only one who tried it in that particular set of rules. Anyway, I could crank the foresight on my C7 (and I mean C7: iron sights) down far enough to get me to 600. Farther back than that, I was pooched. It got even uglier.
It can be done, but it is very difficult. If you want to use irons, a flat-top with a good-quality detachable carrying handle (which can even be fitted with a National Match rear sight) would be a much better arrangement. It has a ranging elevation drum, so you can easily apply the correct range. It beats the hell out of cranking your foresight in and out with a tool and counting how many clicks you’ve come up from the bottom, and praying that you didn’t miscount.
Good luck and good shooting!