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-Revolution 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.
Thanks SW. The plated bullets are .308/150gr. Not ideal. I would think .001-.002 would be better because of the thin skin and soft lead. The noses are flat like a factory round. I got them because I don't want to mess with the expense of gas checks. But, as mentioned, I may be able to coax a bit better accuracy by speeding them up a bit more.
I have some LeverRevolution loads with 150gr flat points as well as some 170s. Haven't fired them yet, but next time out I will. If I could find some slightly bigger plated bullets I would grab a few hundred. A little more velocity may help obturate the base of the bullet better for a tighter fit down the tube; but I cannot go too fast because the thin copper skin can degrade and the bullet can slip on the Micro-Groove rifling. Sure do not want to clog the rifling with the copper or lead.
It will just take time...I will work it out. Now that I know not to get too disappointed with the bigger groups, I can go shoot and have fun, and use KY windage and AR elevation.
I also did some online researching and most responses say 2-3' @ 100 yards is acceptable, so if that's the case I will whittle the groups down and not be disappointed I can't get sub-MOA groups. Now that I had cataract surgery I am shootin one hole groups...ragged, but all touching, at 100 yds. with the Savage .308. I guess now I am spoiled, huh?
One thing I did find was that many of these rifles can use some work on the forend stock. Generally, they're too snug on the barrel and the bands are too snug on the forend, which causes the barrel/stock to bind up too tight when the barrel heats up, and we all know how important proper barrel bedding is to accuracy. If the barrel cannot vibrate properly, the dog won't hunt.