Here is the BSA link (below). I suggest you ask them directly.
Birmingham Small Arms.
BSA made several different air rifles. Unfortunately you did not state the model number and that is critical. You could try to contact BSA and ask them. see the link below.
No
1919-1938. All BSA rifles produced between WWI and WWII were marked "STANDARD." They are all quite valuable if they are in Good to Excellent shape.
BSA actually stands for "Birmingham (UK) Small Arms" they first made guns; hence the 3 crossed rifles on the badge. Yamaha, who first made pianoes, copied the idea putting 3 crossed tuning forks on their badge.
Because of the nature of the PCP power plant I suggest you search the net and look for air gun repair or air gun tune-up. There are shops that tune up air rifles and modify them.
BSA made 8 different Meteor model rifles starting with the MK1 to 6, MK 6 Carbine and a Super. Identify your model and state the condition of the rifle to get an estimate of value.
I am not sure exactly what you mean by "Full Power" so I assume you are asking about one that is NOT sold in the UK directly. The Mark 7 is the latest Meteor model. It comes in both .177 and .22 cal. It is made by BSA. (see the link below.) It is a Springer. BSA does make more powerful models in the PCP class of air rifles. The last reported price was around $300
Well to make 30% stock solution of BSA from powder form you need to dissolve 30g of BSA into 100ml of solvent (water). Thus dissolved solution becomes 30% (w/v) stock solution.
"Best" is a relative term. Ultimately, it comes down to what works best for you. Personally, I'm fond of the BSA Martini .22 rifles.
This rifle must be rare, I can not find any information on it. I did find the following information on these BSA rifles in Mint condition. ( Yes it would be a collectible) Goldstar $450 Superstar $420-$480
Birmingham Small Arms company. The early trademark was 3 crossed rifles. Birmingham, UK was fairly central to the British motorcycle industry.