If you have to sight in at 50 yards, the ST-1 target should work well since it's designed for M72 Match ammo, with a MV ~2650fps and BC near .500 - the same as we've been suggesting for your LR handloads. See this article for some M72 handload information -   (You need to Login

Looking at the ruler on the target, we can see the 1000-yard line is ~19.3" above center bull, corresponding to ~38.6" at 100 yards (drop being negligible from 50 to 100 yards).

If you can sight in at 100 yards and want the same effect, just mark your target some 38.6" above center bull and adjust sights to group there. To simulate a 6:00 hold on the LR target at 1000, use a 4.4" aiming black.