Hey Hutty,
The application of the basics is what you are after. These basics require mechanical aptitude, if you are not mechanically inclined, leave it to a gunsmith or tuner as you can easily muck up a perfectly good rifle or worse hurt someone. Remember that there are three variables that govern what and how we do things, these variables are Time, Money and Quality. Of these three, select two and know that the remaining variable is what will be required to make selected two variables happen. Example: Hutty wants Top Quality at a Good Price he will be required to invest lots of time to get it. Another example: Hutty wants Best price and wants it fast, plan on paying lots of money for the experience.
Material types need to be understood in order to have a low friction interface and some manufacturers use materials that do not lend themselves to be worked to such close tolerances without losing the overall dimension of the product. Case in point, there is a part that is a cast part when interfaces with a bore port, you sand and polish the cast part so it is smooth as glass but now when it is introduced back into the bore port the two parts are sloppy because the manufacturer used the cast seam as part of the overall fit of the cast part. The proper technique was applied but because the base material and engineering used Time and Money variables in production, the Quality of the part suffered.
The basics which have to do with metal working, tolerances, material types, pressures, viscosity, inertia, expansion, contraction and applied physics all sound complicated but so does assembling an IKEA product for the first time.These basics can be applied to any rifle (pretty much) without any expensive tooling. I am not familiar with any video of the basics because typically any video I have seen speak specifically to the weapon being showcased. I would do a GOOGLE search for a step by step to tuning any rifle as these smithing variables can be applied from powder burners to PCP's for the most part.
Be sure that you are properly defining what it is that you are after. Extreme accuracy or extreme power or a fair balance of both. Being that you are in the UK are you trying to stay under the 12FPE rule? If so that makes your quest so much easier because you can simply concentrate on accuracy. The basic rules that you need to apply when tuning a rifle is to measure, measure, measure. You can not fix what you can not identify and if you do not lay down a solid baseline you will never know how close or far off the intended mark you are (pardon the pun). Shoot every pellet you can in 5 shot groups and keep all the hole punched paper for comparisons after your tweaks.
Measure shots strings, FPE for the entire air volume by shooting the rifle until you are off the reg and chart all the data, measure trigger pull weight, measure weight of rifle, inspect and photograph barrel crown, transfer ports, guides and openings, photo graph as much as you can and save all this information as baseline. Next get an exploded parts view of the rifle. De-gas the rifle and begin to take the rifle apart. While taking it apart you are looking for any opportunities to reduce friction between parts. You are looking to debur any sharp edges with a file to eliminate unnecessary wear and tear and friction caused by poorly made parts. Cast parts need to have the casting seam sanded off, openings need to be chamfered, surfaces need to be polished. For instance, the more surface area an object has the important it is that the surfaces be mirror like smooth. Typically cocking bolts, hammers and other "in a port type" mechanical interfaces will require polishing. You can look online for polishing of rifle surfaces sometimes referred to as lapping. Most of these basic techniques can be learned individually to support that portion of the tune, once you know that portion move to the next.
Check the barrel crown, again plenty of videos that talk about crowning yours may be absolutely fine. Trigger work, this is where you can make the most mistakes and possibly create a dangerous rifle. If you do not learn the basics of trigger mechanics you can certainly modify the wrong plane and then you have a weapon that can discharge unexpectedly. If you have not picked up on it yet, I am telling you that there will not be an path for you to understand all the variables associated with tuning a rifle. I have listed some of the things that are required to be evaluated in a good tune but this is not all of them. Fit and finish of two parts is key, the more smooth to parts interact, the better, this tweaking and tuning of the parts is a delicate balance and can easily be botched.
So all this said, what I am trying to impart on you is, take it slow and learn the process steps individually first, then apply them to a test rifle, not your pride and joy so you can learn the processed applied. I know you asked for a video to walk you through all the steps and this response the exact opposite of that but it is important that it be said rather than ignored and in turn a person gets injured or worst killed trying to learn without SOME guidance.
Good luck
Hajimoto
