Quote Originally Posted by Vernal View Post
The muzzle energy has jumped to 11.6 ( I shall keep an eye on it, and may take a washer out if necessary)...
I'd be inclined to set spring preload to give 11.5-6 ft. lb. with 7.88gn JSB pellets (I use Air Arms Express), which should give circa 11.3 ft. lb. with 8.4gn. pellets (JSB Exact, AA Field).

One thing that could nudge the muzzle energy up a little would be the piston seal contracting when very cold, reducing friction, so I'd wait for a frosty morning (won't be long coming now), acclimatise the rifle and then test.