Jet-Z CQBS, specifically for .223 calibres but 'acceptable' for 6mm according to Ase Utra website. Used on .223 remington but rifle now sold. Very compact, efficient and solid! Less than 1 year old, cost £290, £150 plus RFD transfer if required.
Threaded 1/2x28. Jacksons can change threaded insert for £30 I'm told if a different thread is required.