any guesses on why accuracy decreased on bsa scorpion…

bull barrel rifle after I took off my nikon 3×9 scope and put on my leupold m4 10x. My groups went from consistent 1/2″ @ 40 yards to 1″ @ 40 yards.

The start pressure recommended for this rifle is 3250 psi. When I shot the 1/2″ groups I had a start pressure of 3,000 psi. After I put the m4 scope on my fill pressure in my scuba tank was around 2850.

I can’t imagine this lower starting pressure would be the culprit as I have shot tight groups with this rifle before from 3,000 psi down to around 2,000 psi.

I appeal to any masters out there for advice as I am sure you can understand my disappointment in a 1,200.00 scope being outperformed by a 150.00 scope (if that is the case)

The only other thing I can think of is that I did gently insert a laser bore sight in the barrel, not forced….

I was hoping to receive some input before I test it by putting the Nikon scope back on. Thanks.