HW100 Questions

That rifle should have a fill probe with it that will accept a female foster fitting. As to spare cylinders, I have no experience with them but have considered one. Seems some have a check valve to retain pressure (like the stock cylinder) and others do not so research this accordingly. Some are Ti and very light and others aren't. I'm sure some will post more specific information. Is that LA or Louisiana?

The aluminum ones on EBay are lighter and cheaper than the OEM tubes.

https://www.ebay.com/itm/NEW-RATWORKS-Weihrauch-HW100-Lightweight-Cylinder-Air-Rifle-Assembly-Complete-/323597515671

Just for the tube in case you want to upgrade yours.

http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=322659108004&category=52509&pm=1&ds=0&t=1608024225000&ver=0&cspheader=1

https://airtanksplus.com/product/male-foster-quick-disconnect-with-18-bspp-female-threads-w-delrin-seal-stainless-steel/

https://www.huma-air.com/Weihrauch-HW100-fill-probe

I think the rifle cylinder may fit the carbine. You would probably need to remove the silencer before removing the cylinder, but that's not a problem after breaking the epoxy bond that holds it on. There are some larger after-market cylinders, but I think the silencer on the carbine would preclude their use. I have two of the laminate carbine models, like them very much. These are great rifles, but unlike many of the newer rifles, the HW100 offers only modest power and shot count. 

Don't buy a carbine for FAC power. You get stuck with a tiny airtube and it's still as long as a rifle should be. Buy the rifle, and order a 12fpe rifle length barrel that's 410mm. 

OR...

Order a 12fpe rifle from Krale, and turn the power and regulator up to what you like. If you want big power, you will need the looonnngg 600mm barrel. But honestly if you want big power, the HW100 is not the gun you need. 

If you buy a Carbine, and fit a Rifle cylinder, the bulge for the barrel band won't line up, as the Carbine stock is shorter. The straight walled aftermarket cylinders will fix this, and fit fine. 

Don't use the aftermarket ends that come in the Ratworks aluminum tubes. The tubes are fine, but the fill valve end and gauge is absolute garbage. Use a factory Weihrauch fill/gauge end.