I own six of HA's Brens, MK I through L4A4 and my L4A3 and L4A4 work spectacularly well. Early on in the R&D times with Len, we did find that certain guns were more finiky than others, and that removing a coil or two from the striker spring often helped. In some of the early guns the #1 gas port on the regulator was opened up to make it into a "#5" for use with older cordite ammo. I have one of these sitting in my spares bin along with an extra striker spring if you'd like to borrow it to try in your gun.

Drop me a line if I can be of help.

Cheers

Gary