As part of the 4 hour milling and filing marathon that was fitting a Daniels Defence Mk18 RIS2 (bought 2nd hand without the correct barrel nut), I replaced my Hop unit with the cheapo Chinese steel one. My stock HOP rubber didn't have the hole others are reporting, but the loss of bbs from the barrel has been cured, not so much by the unit replacement, but I realised that even with the hop fully on, there was hardly any contact with the rubber, much less any actual hop! Explains the poor range of it too. I ended up carving a bit of 16g silicon wire shroud to slip over the 'ears' on the adjustm