This winter, for a bit of a project I’m going to make a reduced diameter, short action 77. The plan is to reduce the cylinder diameter by 3mm and reduce the action length as much as poss while keeping the velocity in .177 to anywhere between 750 - 770 FPS with an 8 grain slug.

So the air chamber will be reduced to 24mm diameter, the stroke length to around 75-80mm.

So my question to all you shed tuning brain boxes is how much spring do you think I will need to squeeze in to achieve the desired velocity? This will determined how much I can take off the action.

All help appreciated,

Richard