Pistolprimary

Go for the ZCI 6.02 stainless steel barrel. Fitted it to mine and it makes a massive difference. FYI: - If you're changing the inner barrel, its worth changing the bucking and nub. I went for the omega nub and macaron 60 degree bucking. But also note that if you change the nub, you will have to change the hop up unit so that the nub fits in the nub arm. Go for the ZCI m4 hop up unit (don't buy fancy Maxx hop up units as they're rubbish) - If you're planning to extend the inner barrel length (maybe to fit a suppressor or tracer unit) then you may have to change the cylinder inside the gearbox. This is because the port holes are in different places on the cylinder depending on how long the barrel is. The UTR45 has a stock barrel length of 229mm which is perfectly adequate and is fitted with a Type E cylinder. If you extend the barrel length beyond 250mm, you will need to fit a Type D, C or B cylinder (depending how long you extend it). I never bothered changing the length, only upgraded the material to ZCI stainless steel as it is a compact SMG so think its a bit pointless adding a 200mm suppressor on it but this is just my opinion. I've done a fair share on my UTR45 and have also came across a few issues with the replica. Feel free to message me and id be happy to advise on anything.