Take it back and ask for your money back as it is "not fit for purpose" - so you are cancelling the contract. They can't refuse.
However they may offer to replace it (with a new one) which might suit you.
They might also offer to "take a look at it" and potentially to "repair it". If you accept a repair you are not subsequently entitled to get your money back.
You could accept them testing it before giving you your money back, provided that you stipulate you are not wanting them to repair it.
AA TX200, HFT 500, AS400 .22
Daystate Grand Prix & Mk3
Parker-Hale/PAX Phoenix Mk2: .22 & .177