3" at 100 would be good for round nose bullets. Even 3" at 50 is OK for MOD ( Minute of Deer ). What configuration are the Plated bullets ?
For 100 yards and under you might try some Heavier Bullets, They seem to do better at slower velocities, such as the 30-30 usually gives.
When I tried the Lever-Revalation Hornady rounds It did improve the groups. Maybe some like bullets in reloads would do the trick. Of course all guns are different, even same model i.e. Marlin 336. Yours may not like that plated bullet, and it could very well shoot great in another 336.
For 100 yards and under you might try some Heavier Bullets, They seem to do better at slower velocities, such as the 30-30 usually gives.
When I tried the Lever-Revalation Hornady rounds It did improve the groups. Maybe some like bullets in reloads would do the trick. Of course all guns are different, even same model i.e. Marlin 336. Yours may not like that plated bullet, and it could very well shoot great in another 336.