Nikolai,
I tried to post this earlier from my cell but didnt go thru.
The SN rifle sights are not adjustable but you can change the strike of the round by adding shims that came with the SG. Luckily, I have had no issues with accuracy shooting slugs thru my SN TAC at ranges out to 50 yards. Just how far are you expecting to engage a target from?
It is almost impossible to shoot a slug 100 yards with pin point accuracy thru a TAC. Regardless of the sights. You have too many things working against you. Mainly the 18.5 inch smooth bore barrel.
If you didnt want a "scatter gun" Perhaps you should have purchased a full length barrel SN or atleast one with a rifled slug barrel.
The SN TAC is a solid gun and performs its job remarkablely well. Especially, when you realize its a SG and not a rifle.