Never trust what's on the box. There's the short answer.
The most likely difference between the box and your own experience may be barrel length. That would influence muzzle velocity.
The best way to fix it is to buy yourself an inexpensive chronograph and see how fast the bullets are traveling. That's what I did about 7 years ago, and I never regretted the cost -- maybe 3-4 boxes of cartridges worth. For one thing, it will tell you how variable the muzzle velocity is from round to round. That can be a huge determinant in group size beyond 100 yards. Factory ammo is much more consistent today than it was 40 years ago, but there is still a marked variation.
However, you can back into the muzzle velocity with a free copy of PointBlank software. Enter the data from Remington's website, and then plot the trajectory. Now adjust that trajectory by changing the muzzle velocity until you get the drop that you are experiencing.
VIOLA! (Who is Viola, anyway!)
All the manufacturers are extremely optimistic with their published statistics on ammunition, and have always been so. All they are giving you is what they got out of their test barrel with their lot of test ammo. I'm not saying they cheat, but nobody ever seems to be able to duplicate what the manufacturer claims.
I reload and I am able to control a lot more variables than someone with factory ammo. However, even I get a lot of variability in that regard from round to round as I am working up a load. That's one reason they tell you to keep loads under the published max as you are developing a new load. Some of it has to due with the properties of the powder. Some of it has to do with the configuration of the brass. Factory brass is built to conform to the inside of any SAAMI chamber-- not your chamber.