This mod is a bunch of things in one, with instructions for power and 1 for accuracy, it involves modding the valve assembly. I take no responsibility if you use this and it ruins your rifle, do at your own risk. I did it to mine and it works great. It is a detailed process and required a steady hand.
You will need a dremel (rotary) tool with the bits.
I am borrowing StevieLaner7777's disassembly guide.
http://www.airgunhome.com/pages/1077disassembly.html
First I took the entire rifle apart. follow his guide to do that and pay attention to where everything goes, lots of little parts and springs that like to take off, open the casing very slowly. (refer to picture step 4c)
1. I put a small soft foam piece around the barrel about 5 inches up from the valve end and then reinserted it into the shroud, this kept it from moving around and aids in accuracy. (refer to picture step 5)
2. I then worked the hammer spring. All you do is clip off the small hook that is circled in the picture and then stretch out another hook, this hooks back onto the plastic pin. this increases the force of the hammer on the pin.(refer to picture step 7)
3. Lastly, the tricky part that can ruin your valve if your not careful. Totally disassemble the valve and lay it out as in the picture.
1- using a dremel tool with a small, tiny metal ball grinder, hollow out the interior about 1-1.5mm all around being careful not to touch either end where the O-rings go, leave about 1/2cm from each end.
2- using a small, thin, pointed grinding big 2mm, widen the hole on the detent (the plastic part), as much as possible.
3- Next is the valve body pipe feed chamber, take off the brass CO2 feed tube and disassemble the small part that is attached to the valve body, small metal spacer, O-ring, small washer. You will see a small hole that goes directly into the valve chamber, dremel this hole out a bit larger, carefully.
4 and 5- Now to dremel out the valve stem, just widen the length of the hole, then widen the 3 small holes on the bottom, be careful not to touch anything else but the 3 holes, if you slip, your valve stem is dead, all it takes is a hairline scratch to ruin it. (refer to step 10 to 10d)
I found that my valve leaked a tiny bit from the screw in brass end, so I put teflon tape around the thread, problem solved.
Clean everything very thoroughly and make sure it is dry, replace everything, do not put oil in the valve!!!
Reassemble the rifle and you are done, you have just made your 1077, much more powerful. I am not sure how much power I achieved, but a lot because before I tested on a piece of wood spruce 2x4 and it made a dent, now it buries itself over 1 cm every shot at 20 feet. There is an audible difference as well, louder. You will go through more CO2 for sure, almost double.
My next mod will be trying to change to a .22 cal
Thank you StevieLaner7777 for your wonderful disassembly guide, really a great job.
HollowJacket