Check out this guide if you have not already done so:
https://airsoft-forums.uk/index.php?/topic/30669-the-hpa-frequently-asked-questions-faq-wip/#comment-288474
Have a look at air safety information from the UKPSF:
https://m.facebook.com/notes/united-kingdom-paintball-sport-federation/high-pressure-air-paintball-safety-information-guide-hpa-1/349610921821652/
Get familiarization from someone who knows about filling cylinders and about the specific fill station you will be using
You will need an airsoft regulator (for the purposes of this post I’ll xall that the ‘inline regulator’ to step the pressure right down to a suitable working pressure for your gun. This means that you don’t need to worry about any special regulator on the cylinder itself, keep it simple and don’t worry about SLP cylinder regulators - these are nieche market regulators and can be counter prodctive by being too slow at refreshing your inline regulator.
Again don’t worry about fibre wrapped cylinders etc. For the bigger size and higher 4500psi pressure capability you pay more money at about £150 for the cylinder & it’s regulator in comparison to a standard 3000psi aluminum cylinder at about £40
The maximum 3000psi or 4500psi capacity of the cylinder has no bearing on how it operates your gun.
A typical fibre cylinder is lighter than the equivalent sized aluminum cylinder, but not by a lot to justify £100. You can get a noticeable weight difference if you get an ultralight cylinder but are then paying more likely £200 for the cylinder with regulator
Fibres have a typical lifetime of 15 years before they should be scrapped and need hydro testing every 5 years at between £15 and say £40 not counting any postage, probably an average of £25. So you are now looking at £200 over 15 years
Drop or bash a fibre cylinder and scuff it’s coating and I’ll reject it for filling
The true benefits of carbon fibre in paintball is the right size and balance to fit the ergonomics of the individual with their gun using the cylinder as a stock
As soon as you take it off the guns and use a remote line you have just discarded those benefits
Aluminiums have an unlimited lifetime as long as you hydrotest then every 5 or 10 years. But at about £40 new you may as well replace it
(Note that most documentation and markings say 5 years, but in the UK the legal requirement for a true aluminum 3000psi cylinder is 10 years or a 13ci aluminum cylinder is exempt from hydro testing. Not all sites / organizers will accept the 10 year or unlimited timeframe and will err on the side of safety and allow you only 5 years. If it’s one of my events and I’m the air checker then I will allow 10 years / unlimited subject to my visual opinion on condition
Scratch the paint on an aluminum cylinder and I won’t care
4500psi cylinders give you 50% more air as long as you have 4500psi fills available
But if you have air fills on site then why bother carrying a big bulky bottle when a 13ci cylinder will be perfectly fine?
If you don’t have air fills available on site then I would be less inclined to want to carry a realistic style gun, with a hose and big air cylinder when you could just as well put a battery in it
(Also if you don’t have air fills on site then buying 2 standard 3000psi cylinders gives you double the capacity just by swapping cylinders at £80 for the pair as opposed to only 50% more for £150)
Summary / your questions:
What size?
I would say a 13ci 3000psi is nice and convenient otherwise a standard 48ci 3000psi
(I don’t know what shot capacity you would get)
Aluminium or carbon fiber?
Aluminium
Difference between SLP and HP cylinder?
No difference, only the fitted regulator output pressure and possible higher cost
Regulators?
Just use the standard cylinder regulator and then go for a suitable inline regulator to step down the pressure for your gun
Buying the cylinder
Shop around, it may cost you more for a cylinder from an airsoft retailer, go to a paintball retailer and you may pay less for the same item
Even better buy it in a real physical shop it you can to save on postage and to take a peek at the manufactured date to get the newest possible from the stock as they may be a few months or a year old on the shelf
