The only issue that I know of is when loading the 260 for a large frame AR is you have to seat the bullets deep in the case to fit the mags.
This removes any advantage the 260 would have over the 6.5CM as you are losing case capacity seating the bullets to mag length.
I went through the same thing recently....building a MaTen based rifle. I ended up going with the 6.5 CM. very happy with it. I used a JP barrel kit. Do a search on my user name and you can see some pics of the rifle.
Bring hay for my horse....wine for my men....and mud for my turtle!
"A fear of weapons is a sign of retarded sexual and emotional maturity."
- Sigmund Freud
Originally Posted by ar15barrels
It makes it bigger and longer.