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?

Try it underwater

Quoted: Try it underwater

............but post the video  

I have the wooden forward grip.

ilikelegs, do you recall the position of your trigger finger? and the rest of the fingers on trigger hand??

I've tried it with and without a forward grip. I actually do better without one. I have done most of my bumping with ARs though. Whe i bump from the shoulder, I have my fingers just like you do. It usually works when I have my thumb around the grip (but not really holding it) but sometimes it works better to put all 5 fingers on the outside of the grip. I hold all of the straight forward except my trigger finger. My favorite bumper is my Bushy Carbon 15 P97S. I have a RRA 2 stage trigger in it and the damn gun weighs nothing....so it has a bit of recoil and that helps. Sometime it works best on that gun if I seem to throw the gun forward kinda roughly instead of smoothly pushing it forward.

My $0.02

Good tips HK_DUDE. thanks

Be careful.  Bump firing can cause you to go blind.