reloading has its pitfalls and this was one of them
I had been using a No4 for doing the load testing and got the load and velocities on the mark then assumed that they would work in the BREN.
It turns out the chamber difference between the No4 and the bren were enough to cause the cases to stick in the chamber and cause them to be hard to extract. I was using lee dies which are oversize like the late war/American chambers so they were not sizing the base back to the size it should be on new brass. Once I sized all the brass on a tight die the problem went away.
I got in a bit more range time with a bucket of reloads and had 1 stoppage that was a mag/feeding problem. With only that 1 stoppage it was a fantastic day.