Just a quick update - Fitted the original HW99 barrel back on and quickly put about 30 JSB Express pellets through.

Power up to 11.3ft/lb (Vs. 10.2ft/lb in the HW50 barrel) and accuracy much better. Last 10 shots in about a 15mm group, which I'd expect to improve after a few more shots and leaded in. Didn't bother testing any other pellets as the barrel will soon be coming back off!

Had a reply back from the German Supplier 'Versandhaus - Schneider' asking me to return it, along with a prepaid postage label. Certainly can't fault them, and hopefully the new one will be a lot better.

Will update accordingly