I shot a few pellets today with the modified 600s. Both of these 600 were hot valved by Dave Gunter in 2011, one has been resealed since, no work on the other & still working well, like a well tuned sewing machine. I put the scope mounts on & bought the barrels online. I made the base short and drilled a hole in receiver. Most people use the barrel grub screw hole for a longer base, but I like to be able to get to the breech, w/o removing base. I admit this ruins the gun for collectors. The 600 with the scope shoots @ 470, the other 430. Cool today, will shoot faster when warm. Top groups are crosman 14.3 , bottom target H&N Wadcutters. Both pellets function great, but the H & N are more accurate. The best group I got today was a lil less then 3/8" ctc. All groups were 10 shots # 33 feet. The 600 with scope & bull barrel is most accurate as you can see. The other shoots about 1" groups at 33 ft.