A few years back a good friend of mine won a Stainles-Steel Encore and choose a 15" .243. He wanted a .243 so he could use it on Coyotes and Whitetails.
At any rate he picked up some Factory Ammo (80gr. Winchester PSP and 100gr. Federal Hi Shok PSP if I remember right). At any rate I could not get either one of those factory rounds to print under 2" at 100 yards. I then set out to work up a handload for my buddy. I tried 55gr. Nosler Ballistic Tips, 80gr. Speer Hot Core Spitzers and 95gr. Nosler Ballistic Tips.
In the end we settled on the 80gr. Speer Hot Core Spitzers loaded with H-4895. Muzzle Velocity with the load we settled on averaged 2920 FPS, and 5 shot 100 yard groups from the bench averaged 3/4". I used this Handgun / Load on a Anterless Deer Hunt on Jan. 1st of 2007 and harvested two Whitetail Does at slightly over 200 yards and it worked great.
If you are not a handloader, Federal in their Power Shok Factory Ammo uses the 80gr. Speer Hot Core Spitzer Bullet. While I have not shot any of this ammo to know what the accuracy potential is or the muzzle velocity, I do know this bullet works well.
As per the vertical stringing in your groups, as has been pointed out it could be shooting technique, or forend pressure on the barrel or the forend screws not tightened evenly. In short it could be several things, one of which could just be the ammo.
Larry
