I can bump from the hip with a SAR-1 just fine, 30 rds just like that.
However, I cannot bump from the shoulder.
For the hip, I keep all my fingers straight and index finger locked, thumb behind grip but straight and not really touching the grip. The trigger contacts the pad on my index finger next to the biggest knuckle (where a ring might sit, 3rd pad from tip). I keep the right hand still and pull the rifle forward with the left to fire.
When bumping from the shoulder it is hard to lock my index finger. I also think I may be pulling the trigger instead of pulling the rifle forward as it is harder to support the weight of the rifle with the left hand from the shoulder without using the shoulder stock. I do have a forward pistol grip which does help with holding the rifle up with one hand. It's close but no cigar yet.
I may try the 'swingset' shoulder bumping device till I get the hang of it.
Does anyone have some tips for shoulder bumping? What position are your fingers and where is the trigger contacting?
Also, I have a question about rate of fire during bumping. A couple months ago I was getting a very fast ROF bumping from the hip. The last couple times I did it the ROF slowed down considerably..... then my recoil spring retainers broke.
Does the recoil spring strength alter the ROF while bumping?