I ordered an 8X57 JRS barrelx to be installed in a 16 ga drilling’s right shotgun. barrel. It had to be proofed in Germany. And an import permit was required to bring it to the US. It was made specifically for my gun. It installed with no trouble but after a few shots the insert barrel started rivelling, showing plastic deformation. The insert was destroyed and the maker refunded my cost. After that only rimfire and 22 centerfire inserts were used. I have several for sale in 22 rimfire and 22 Hornet for 12 ga.
