... Years ago when I was shooting the 3 gun matches, the 870 was all I could afford/borrow. The magazine extensions does shift the point of balance/handling, were I to shoot the three gun matches again, I'd DEFINITELY go with a semi-auto (your choice of Brand) with an extended magazine, one that didn't quite go to the end of the barrel with very strong clamps holding the barrel and tube extension together and forming a solid mounting point for the sling. Probably, based on personal bias, a Remington Wing-master, adding only the sling and extended safety button(and the extended magazine tube) .... the semi autos are faster, and eliminate the chance of "short stroking" a pump gun, and you don't need Magnum shells either ! .... David K... ps The Migratory Birds Act mandates the 3 shots when hunting duckies etc.otherwise, basically, no plugged 'tube.