I tested the grip vs velocity on a springer - quite crudely - about 5 years ago.

I held a hw97 in a number of different ways - while shooting through a chrono.

The tight holds had the velocity bouncing up and down like a brides nightdress.

The more passive holds had a much better result.

I know all thats not news, but it was clearly visible and proved that most springers - even the least hold sensitive - need a consistent shooting style.

PS - my 97 had a macarri (CS) stock on it - loaded with lead and in the butt had lead shot held loose, so as to kill recoil dead blow hammer style.

Also - I found an AWESOME way to bed a springer into a stock once.
Sheet lead cut into a semicircle and pressed home behind the trigger block and the stock.
This planished itself into an amazing bed for the back of the rifle.

We are not talking thick sheet, just 1.5mm thick.

Most model shops round here sell different small packs of sheet metals for the craftists, with a selection of guauges.

I bought some brass too, to shim a scope mount - as i am led to believe - brass has a low shift in temperatures.