Sorry but I retired from the Airgun Tuning business all together about two years ago. I no longer have any parts or machine tools for tuning. I had retired 3 times in the past and it didn't last long so this time I sold the tools to make sure that I stayed retired. lol
Why a Springer airgun tune
It is important to understand that tuning a gun does not necessarily increase the fps (and usually doesn't) unless there are issues such as a broken or fatigued spring, a damaged seal, or a rough chamber wall or a combination of those conditions and others. The logic in a tune is to extract the efficiency of the gun, to make it a smoother, more accurate, with more consistency and efficient with less spring vibration and twang and reduced recoil with an improved smoother and lighter trigger pull making it a more pleasurable shooting gun.
What a tune does and why it's important, whether I do it or someone else does it.
First: I have yet to see any lower end guns, especially in the Chinese rifle's using synthetic seals not having at least some damage, often times minor, and some with sever damage, which the buyer will never know even while shooting it unless it is extremely bad or he breaks a spring or he has a Chrony and can see the power loss. Secondly: again, especially in the Chinese clones, the vibration or spring twang and torque caused by poor or incorrect lubrication, and poor quality control, rough components, and poor spring design and construction causes' inconsistency, loss of power and inaccuracy. Thirdly: either little or no lubrication, or incorrect lubrication of other critical internal parts. Fourth: smoother, softer, and depending on the gun, shorter more predictable trigger pull, and finally, resolves most rough cocking conditions.
Spring twang or vibration and cocking roughness.
First there is the roughly finished metal on the interior parts caused by poor machining and stamping. Two dynamic things that happen when you pull the Springer trigger. First there is double recoil. When the seer releases the spring, the gun starts to recoil to the rear. Then when the piston hits the bottom of the cylinder, it drives the gun forward. The second thing is that as the gun is cocked, the spring expands and at the same time twists slowly until the piston is latched by the sear. It may also cant or bend the spring during this process. When fired, the reverse happens, but in a fraction of a second. The twisting during decompression causes the rifle to twist in the opposite direction of the twist of the spring. For every action, there is an opposite reaction of course. A tune helps reduce much of this violent reaction.
Tuning, if done correctly and depending on what kind of tune, reduces spring vibration or twang, increases power, and makes for a smoother cocking operation. In addition, there will also be a softer more predictable trigger pull if a trigger tune is done or the GRT-III trigger is installed (a far superior trigger with a lot lighter trigger pull).
Another important result is far less recoil, less twist (torque), more consistent, and will be more accurate shot after shot requiring very little service (lubing and maintenance) for the life of the gun.
Keep in mind though, springs do break on occasion and seals do go bad and are considered a where and tear item. I use nothing but the best seals and springs available for the particular gun. The best $30 for basic parts you'll ever spend on a Springer. If special kits are used, such as a TurboTune kit, or the GRT-III is installed, the cost will be a little more.
About the proper internal lubrication.
Proper lubing is of the utmost importance. How it is lubed, at what points it is lubed and what lube is used on those points make a tremendous difference how your gun behaves, its accuracy, it's consistency, seal and spring life, and it's longevity. It's important to know that there are several lubes used in airguns for different purposes in different locations and they all play different roles.
So many things are resolved by a good tune and these principles apply to all airguns. You just can't beat the money spent for a tune, especially if it's tuned properly.
But please keep in mind, no two guns are the same coming off the line, or tuned by the same tuner, have the same power and consistency. Secondly, power should not be the primary concern, although important. If it's tuned and comes out extra strong, that's fine as long as it fires smooth and is consistent. If not, it should be 'de-tuned' a little.