I just got a new fully rifled slug barrel for my Remington 1100. Is their a proper way to break it in? Also, will firing non-sabot slugs harm the barrel? I know the non-sabot slugs will not be as accurate, but for zeroing in the scope to get it on paper I hate to waste expensive slugs.

because you asked this question i will give you a little bit of free advice.  you don't and can't break in the barrel.  normal rifles have small burrs on the lands and groves and cleaning them every few rounds will help the jacketed bullets to smooth the burrs as you fire.  if you don't clean carbon forms around the burs and the barrell nevers smothes out.  plastic sabos and lead are too soft to smooth the bore.  firing non-sabot slugs will not harm the barrel.  get several boxes of slugs and shoot them all in your gun to see which slug your gun shoots the most accuratley.  then buy about 100 slugs of that type.  save them and shoot them only in that gun.  the range of your weapon is 0-50 yds.  learning to shoot a slug gun at 100 yds is a challenge.

put some blue locktight on your scopes rings, base and any small machine screws on the gun.

In my part of the world....we must use shotguns.....I have four different shotguns with rifled barrels......here is MY experience......no break in with a shotgun....rather...find WHICH slug works best for you.....when you do....use ONLY that slug....regardless of the cost of ammo......if it cost $40 to site in your shotgun...and you get a deer with one shot...what was the cost?......there is such a HUGE difference in performance between sabots and cheapo slugs.....that my opinion is...I will not use lead slugs in a rifled barrel....does it hurt to use them? no...but...rifled barrels were made primarily to use sabots.....so??? if you have a cantilevered barrel....once you sight it....it should be good and only a minimal amount of checking every year will be needed.....if it is a reciever mount...then maybe a little more....one other thing....most guys have a dedicated deer gun...some of it is superstition....some of it is common sense.....make up your own mind on that one....but as far as I`m concerned...trying to save $ by shooting lead through a rifled barrel is actually a waste of time AND $$....

Non-sabot slugs work fine out to 100 yards - in some guns they shoot better than sabot slugs.  My old pre-sabot barrel doesn't stabilize the long sabots well at all.  No break-in required.  My advice is to start casting your own slugs, load some light to moderate loads for practice, and blast away. :)