Firstly, you will have to have a defence against an offence of importing a RIF under the VCRA. UKARA is one way of proving this defence, being a site member and having either a letter from the site, or the number of the manager of the site who will vouch for you.
As it is coming from a member state of the EU, there is no import tax to pay as long as the item is for personal use and not for sale.
So you could buy the gun from your uncle and either bring it back with you, carrying along with you your proof of defence (land based transport would be better for this as getting it on a plane could be difficult. Some airlines will allow it with proper proof, others won't.
When you enter the country, or at customs, you should declare the item, and show them your evidence of a defence. There should then be no problem.
If you get your uncle to post the item, then get him to put your contact details on it so they can get hold of you to ascertain whether you have a defence to import.
There's no reason not to do it, and it can work out much cheaper, as long as you make sure you have all the necessary in place first.
