First off since you have a rifle barrel stick with sabot slugs for the best performance.

You never stated what gauge your shooting nor the type of sabot slugs (many types within each ammo maker), what length slugs, weight, etc.

Did you have the scope bored sighted? Make sure you check the scope mounts, they could become loose. Also, I see this often that the stock of the gun maybe to big for the shooter, this in turn will hamper the shooter from getting a proper sight picture, in turn causing bad shooting. I cut my stocks on all my firearms somewhat more then I need to make up the difference for bulky clothing during the gun season here in New Jersey.

Once you find the proper sabot slug for your gun, sight in at 2" or 2.5" high at 50 yards, this will put you within the kill zone out to roughly 100 yards.

I notice over many years the Lightfield 2-3/4" EXP slugs work great in almost all shotguns. Your Remington barrel has a 1 in 35" twist, that is a slow twist but common in slug guns, I have that barrel on my 11-87 the Lightfields work the best for me. Hornady, Winchester Golds, X3, Remington Core-Lokts, Federal Barnes, and similar sabot slugs work better in barrels with a faster twist.

Try the Lightfields, sight in at 2" or 2.5" high at 50 yards, I think you will like them, but once more check the scope if its bore sighted and the mounts are tight