na, feeds just fine from any 6.5 grendel AR-15 mag I've tried so far. E-landers and ASC mags are what I've tried and they work great, I haven't tried any C-products mags, but I'm sure they would be fine as well. the magazine is held at about the same height on a bren as an AR, but the feed ramp is less steep and as both the bolt lugs and the barrel lugs are longer (as in total outside diameter and front to back) the jump into the chamber levels out more during the feeding process.
I'm not much of a film-o-grapher or whatever, but I may take a phone video when I take it out. not sure when that will be, but hopefully soon.