Fronteria, do you know if your carbine had previously been saw cut?
I got my fingers burned (figuratively speaking) on a MH MkII Artilery Carbine I bought from a stall at the Antique and Classic Fair at Bisley a few years ago. The gun wasn't fabulous, but it looked the part and the bore was nice and firing pin in tact. I forked over the requisite amount and took my purchase home. Over the next few months I collected all the stuff together to re-load for it and once I'd done that I got it put on my ticket for use. The first shot I fired was a light load and went off well enough. All seemed well untill I came to eject the empty case; it was stuck fast
. After alot of hammering and swearing I got the case out and saw a strange ridge accross the case neck that looked like the negative impression of a groove cut in the chamber. Sure enough, the carbine had been saw cut in the past right at the front of the nox form to make it a D.P. rifle. What some one had then done was weld a half washer in the cut and smooth off the weld on the outside
. I have to say externally the job was very good and it was impossible to tell it had been done. I think the only thing that prevented that washer blowing out was the case. If it had been cut further up the barrel I recon it could have burst, or at least blown the washer out vertically.
So when I look at a MH now I always check the top, internal surface of the chamber with a small dentist's mirror.