simple bro...
1-convert weight to kg by dividing by 2.2
2-then mulitply by BMR factor (1 if you are a guy)
3-then multiply by 24 (to show how many calories your body needs per day)
4-the take this number and multiply it by your activity level .65 and .8 for moderate level and .9 and 1.2 for heavy level. most of us on here would be moderate level unless you are working out ed, which you shouldn't be when bulking anyway.
5-so now you have 2 numbers, add each of them to the number you got in step 3. this is how many calories you use per day counting how many you burn exercising.
i'll do it for you...
260/2.2= 181.18
181.18 x 1= 181.18
181.18 x 24= 2863.36
2863.36 x .65= 1843.64
2863.36 x .8= 2290.69
1843.64 + 2863.36=4707
2290.69 + 2863.36=5154.05
so to maintain 260lbs you need between 4707 and 5154.05 calories per day.
like big byrd said too, metablosm and bf% plays a big factor.