Comments by "Steve Valley" (@stevevalley7835) on "Type 93 Long Lance Torpedo - Long Range Hole Poking Device" video.

@erikgranqvist3680 it was pretty routine for the liner to stretch as the gun is fired repeatedly, so the end of the liner would stick out of the muzzle of the gun. That was not a big problem as the exposed end of the liner could simply be sawed off. You have probably heard of "copper choke" where material from the driving band of the shells builds up in the bore to the point where it impeded the shell. The effect of the shell being impeded was excessive pressure in the barrel, eventually leading to the muzzle and chase being blown off. Tools were developed to scrape the buildup out of the bore. A more serious problem on some of the early guns was "steel choke". In some early guns with liners, as the liner stretched, it would form a ridge in the bore. Eventually the ridge would grow to the point where it impeded the shell, and do it suddenly enough to initiate the fuse in the shell. Early liners were machined straight, and changed by heating the barrel while cooling the liner so the difference in thermal expansion would loosen the liner enough for it to be pressed out. Sometimes, the liner would not come out, in spite of the heating process and had to be machined out. Each pass of the cutting head would take several days, so it was a matter of weeks to completely machine out a stuck liner. Gun factories learned to machine the OD of the liner with a slight taper so it would be easier to press out.
5