Care should be taken when handling the barrel to avoid damaging it it any way.

Pic 1 shows two 12” Stealth barrels. Note that I have mirror polished the breech end of the upper barrel to minimise frictional losses, evidenced by the scuff marks on the lower, unpolished, barrel.
As stock the breech slide area (the smaller diameter area of the barrel) is often very rough. As the Breech Slide ‘O’ rings bear on this surface, a polished finish will both preserve the seals and improve efficiency.

Pic 2 shows an assembled barrel with one of the Delrin spacers replaced by a series of steel washers. These washers are the exact dimensions of the spring spacers and may be obtained in many DIY stores (these were sourced from B&Q).  Being heavier than Delrin they effectively increase the sprung mass of the Hammer group as acted upon by the spring - the same effect as replacing the Hammer with a heavier one made of alloy.

Note also that the lower barrel has had it's mounting rings removed and the upper barrel has only the one. These rings may be removed quite easily but need to be gently drifted off the barrel. I employ a wooden 'former' with a 'U'-shaped cutout the radius of the barrel. This is then fitted over the delrin mounting while the barrel's muzzle end is rested on a piece of soft wood, and the 'former' tapped gently to drive the mount off the barrel.

On reassembly, care must be taken to realign the barrel mounting rings so that they align correctly with the 2 mounting holes in the rifle frame.

NOTE 1:  Be aware here that spacers can be added to either end of the Hammer Spring.

Those added to the left will have the effect of simply preloading the Hammer Spring.

Those added to the right however, will have the effect of both preloading the Hammer Spring AND increasing the Hammer’s mass as they will travel forward with the Hammer under spring pressure and strike the Breech Slide.

NOTE 2: Care should be taken that the overall length of the Spring and Hammer group is not increased unduly as this can cause spring binding during reassembly and prevent engagement of the Hammer during cocking.  

 Depending on the actual rifle you have, you may find up to 5 of the small plastic rings approximately .5” thick. The ones shown here are whitish in colour - some are black. These are Hammer Spring preload spacers and are factory fitted to bring Hammer Spring tension within tunable limits. As previously discussed, adding to these can improve the consistency and power output if desired. These spacers, and any further packing, should be fitted between the spring and the barrel mounting ring unless you wish to increase the Hammer’s effective mass when additional spacers may be fitted adjacent to the Hammer. Be aware that increasing the hammer’s mass and spring tension will dramatically alter the performance of the gun by increasing the force with which the valve is struck by the hammer and may make the rifle illegal in certain countries.