Hi Ed, most shotguns have an effective range of 30-50 yds with buckshot. You may be less than that with an 18" barrel. The best way to find out is to shoot some buckshot at the range to find out at what range your pattern is no longer viable.
Stay safe & have a great day!

Yeah, as mentioned below. 50 yard max but 30-40 yrds very effective!

Hi Edward and welcome. It has an 18-inch barrel and effective range will in part depend on the Buckshot load. Not all are created equal. With the Cylinder Choke, the best effective distance load out to 50 yards in the Federal Flit-Control Buckshot load here: budsgunshop.com/product_info.php/products_id/36183/federal+pfc15400+premium+vital-shok+12+ga+2.75+9+pellets+00+buck+round+5+bx+50+cs ---------- Cheers, stay safe and pattern well!