I live in Washington state, and several parts of the state have firearm restricted areas that do not allow centerfire rifles. I was drawn for an elk permit in such an area. I bought a Remington 870 with cantilevered slug barrel (fully rifled), and mounted a Nikon scope. After testing various brands of slugs (ouch on the shoulder, and the wallet!) I settled on the Winchester Platinum Tips. What is odd and frustrating is that I can shoot very good groups, most of the time, at 50 yards. However, at longer distances such as 100 and 200 yards the groups really open up. Specifically I can shoot 1 to 2 inch groups at 50 yards, but at 100 yards they're 4 to 6 inches, and at 200 yards they often a foot or worse. They do not follow a typical "MOA" progression as my centerfile experience would suggest: 1 inch at 100 yards is 2 inches at 200 yards, and so on. The projectile is a .50 caliber slug nestled in a sleeved "sabot". The slug weighs 400 grains. The muzzle velocity is 1700 ft/second. I've heard, but not confirmed, that the barrel twist on the 870 is 1:36. Someone told me that Benellis have a 1:28 twist, and thus will stabilize such sabot slugs better. According to my calculations the slug should go sub sonic at around 175 yards. Could it be that as the slug slows and approach the speed of sound it begins to experience turbulence? It could be my shooting, but I humbly suggest that is not likely as I've shot a lot of centerfires with consistent results. I changed out the scope and that does not appear to be the culprit. It could be the cantilever mount, or something with the stabilization of the projectile. Any thoughts?