To be honest, you rarely get hit for tax on parts, which come from HK or mainland China - for me the average is about 6/7 packages get through, without being touched by UK Customs. That may vary, if you are somewhere else, of course. My guess is that, the volume of parcels coming from the far east, is so large, that they just do not have the manpower, to deal with them all.
I have used extra punctuation, to divide ideas up, so that Google Translate will work better.
Edit: but you almost always, get charged tax, on guns. You could retrofit the RIS gas tube, to another AK...