Thanks Jim. It is one of my own design and manufacture, aluminium outer, stainless steel innards, very quiet and enhances accuracy. The rifle is a Chinese Ranger, chrome lined 20" HB, 7" twist, and very good quality (fully the equal of anything from the US). It gives consistent 0.5 MOA 5 shot groups with 69 grain Sierra HPBT match bullets. It took out a billy yesterday at a lasered 509 metres (two shots unspotted, third shot just a smidge high, fourth shot kill).
I have increased the bolt travel on the Charlton to give a 3mm clearance behind the rim of the top cartridge (it only had 1mm before), and still avoided the bolt head taking any impact at the back of the stroke. Hopefully good results at the range tomorrow.