small as pellet damage will occur otherwise. Have only done one and did not tune it to much as it was over 700fps easy. Probly can take the port up a sixty forth of an inch or so. Does not sound like much but doesn't take much when you are already over gassing the gun in the .177. You want a looonng barrel too to make use of all that gas. On the pistols I usually put in a lighter hammer spring very little fps loss and more shots.
I used to have a life. But now I have the forum. I am a sick man?