warthog
I can't see either pic for some reason, but hear this. I had a Buffalo Classic that shot as bad as your 243. I tried all sorts of loads through it and it shot patterns, not groups. I called NEF and explained what I found. For one thing I had slugged the barrel and found it was several thousandths tighter just past the chamber than anywhere else in the barrel.
I believe the bullets got resized just out of the chamber and the rifling in the rest of the barrel was useless after that.
I sent this info and the gun back asking for a new barrel. Well it took some talking and a call to the Pres of Marlin and I got a new barrel. The delay was a supposed breakdown of ventilation equip on the indoor range. This went on for a month until I called.
NEF said they couldn't test my gun till the range was fixed. I guess the Pres of Marlin didn't agree. Anyway I got a new barrel and that baby could shoot anything. It gave me 3/4" groups at 100yds with tang sights.
My point is, first call NEF and ask what ammo (factory?, brand, bullet weight etc.) they shot on your "test target". Next, ask if they did anything special as far as holding the gun (sand bags, machine rest, etc.).
If they tell you all this and you still cannot group it, have someone else that is a good shot, (not saying you are not, just a second reference to them) and if it still flips bullets of the same make they claim to use, send them the targets and ask for another barrel.
I had a friend at the range that swore his new Remington 700 7MM Mag, was crap cause he couldn't get better than 4-5" groups with it and blamed the gun. He went through about a box an a half of ammo to try to zero it.
Another friend that was helping him asked me to shoot the gun. I easily got 1 1/2" groups. I think he was flinching badly. Not used to the 7MM since it kicked a lot more than the '06 he used to shoot.