im kinda chasing GG there ^^ my Bren IS set up in 54r and 303 both so you can look at some of my pix if you want ...
made acouple of small changes to get it to all work right cause most of my 54r is the light ball stuff.
drilled out the gas port even bigger in the regulator and the barrel holes... so i have one port for 303 and one for 54r.. ( could have just got 2 regualtors i guess.)
then used the zb39 mags with no issue at all.
did have to do a little work to get the headspace right as im using 2 different bolts on the same carrier.. took some playing but it runs fine.
the 54r does not feel as smooth as the lower powered 303 and its not as accurate either.. but i can afford to shoot it.
Trenches and me send pm's to each other all the time so im sure he doesnt mind me putting this post in his thread. if he does, i'll take ti out.