50yds is a bit far for doves if you're shooting a low brass shell. If distance is what you're after, you have two options: larger shot size or larger powder load (or a shell that gives you both) I've used #6 in a high brass load for doves. It hits 'em hard.
There are some other options that can cost a bit, like handicap or sporting clay loads in #8, or the non-toxics. Non-toxics are not really made for wing shooting applications, but will work, make sure your wallet's thick enough though.
Are you stuck on using a MOD choke? I shot mostly IC at doves. Using MOD in my 12ga seemed to bust 'em up a little too much, my 20ga is just the ticket for me. IC can do a lot in wingshooting applications.
12 ga shells I've liked include:
-Win. highbrass-heavy game #s 8, 7 1/2 and 6
-Wolf dove & quail
-Fed. highbrass #s 8 & 7 1/2*
-Estate 7 1/2
*also tried some Fed. #9, but it wasn't common and more $, and not really necessary.