a friend of mines .260Rem is having trouble chambering rounds. The bolt is sometimes a little tight to close and the cases have what looks like marks of where the necks are catching the riflings.Hes using factory Remington 120 BTs. Any reason for this and probles it may cause?

Check his unfired ammo, the marks sound like collet crimp marks. If it was the brass hitting the rifling, the pressure spike would be high enough that we wouldn't be having this conversation (he'd be talking to his orthopedic surgean and his lawyer).
If the hard part is in closing the handle, check the rim diameters and chamfer, the Rem extractor design requires forcing the extractor ring over the case rim.

Are you certain the brass isn't simply too long. If so it will leave the imprint marks of the rifling on the case mouth. It could also be that the case isn't sized fully or even that the primer isn't all the way home. Best wishes.

Cal - Montreal

if it's a stock Remington Rifle with off the shelf Remington ammo, I would call Remington.

If it's handloads or rebarreled rifle, that's another story.

I once had the same problem. I neck sized a load of .243 brass for a really accurate load I'd worked up. Some of the brass wouldn't chamber. I then remembered I'd taken some of the brass my neighbor had fired in his .243.

Steve

we have encountered some rough chambers this past year or two. Sometimes they don't catch a worn reamer in time. Do you see lengthwise scrathes? they don't have to be the entire length,..even a very small length will do it. If so,..the chamber/neck has some burrs and these can be polished out. They will sometimes also be a bit hard to pull out of the chamber.