The bolt spring is too strong for the soft metal they use in bp cylinders. This is pretty common. You can get a replacement low power spring from Wolff springs. They offer a replacement flat spring and also a music wire spring. I have found that the trigger side of the replacement springs is just about a hair short of perfect, and while it will work, it is a little tricky to install so that it keep contact with the tooth on the trigger during the entire installation. And while they are better than stock springs, they aren't that
much lower power, or at least the 8 of em I have are not.
But one fix that you can
do at home,
and quite easily, is to feather the bolt spring a little, either with some very fine sandpaper or using a Dremel tool (I don't like Dremels, but I mention it because they are so popular) and just thin down the bolt leaf of the spring to take a little strength out of it. Do not alter the trigger side of the spring, that is not safe for amateurs to modify.
You can just do some searching in the smithy forum or google how to feather a spring if you aren't comfortable with it.
You should also use some fine sandpaper (I like 600-800) to break the edges of the bolt face so it isn't so sharp on the corners and it will reduce gouging of the cylinder lead-in ramps. Do not round off the bolt, but just barely
take the knife edge off the corners of it and slick up the face to a nice glass-smooth surface.
Ideally, the timing would be tuned so the bolt drops into the locking notch perfectly upon full cock, but this is a job for a gunsmith. It is very tedious work and you'll go through a handful of bolts before you get it right.
It's a more achievable goal (and perfectly functional) for you to get it to pop up about a bolt width before the notch, contact the cylinder without gouging a big dent in it, and then just slide down the ramp and into the notch.
You do not want to time it so close to the notch that it pops up and just clips the edge of the notch before it goes in, or it will peen the metal from the side of the notch down into the notch itself. So if you mess with the timing, it must be perfectly in line
with the notch, or at least a bolt width before
the notch when it activates.