When you mounted your scope did you mount it straight? the front base and rear base have to be " square" . This problem does not show up untill you shoot at ranges of atleast 100-200yds. Also with any new gun after the first 20-40 rounds you should check the screws that keep the barreled action in the stock, they sometimes will shoot loose, again causing problems at longer ranges. some other thoughts:

What are you useing for a rest? a proper benchrest will improve your groups I guarantee it. You can buy a fairly nice one for around $50.00

When you shoot at the shorter ranges then move to the 100 yard range do you change the setting on your scope? Don' t take offense, I learned this the hard way, with the cheaper scopes (i.e. Bushnell and others) sometimes when you change the power setting you change the impact of the bullet.

What type of target are you useing I have found that the diamond type targets are excellent for checking benchrest accuraccy. They give you a consistent aimpoint, by leveling your crosshairs in the corner of the diamond.

Also the Remington 710 should shoot o.k., granted it won' t get invited to the prom.
You should expect a group no larger than 2" , which is fine for hunting accuraccy say to 300 yards.

Most .30 caliber rifles favor 165 grain bullets.

Buy 3 different boxes of ammo with the same bullet weight. Shot all three from as stable a rest as you can find. I try Federal first.

Also why working off the bench turn your scope to the highest setting and shoot your groups. 5 or 3 shot is o.k. Rember to let your barrel cool. When shooting from the bench you are testing your rifle/cartridge accuracy not your shooting abillity, that comes latter. Once you get the load that you will hunt with sighted in turn your scope down to the magnification that you expect to use while hunting. Shoot a few more off the bench and make any final adjustments. Then leave the bench and shoot from modified field positions, that is what you will use in the field.