Originally Posted by
303Guy
I did some developments for my ancient carbine which was a Martini 303 carbine barrel on an 1896 Lee Enfield action. Now this barrel is worn like the rifling is rounded and the bore quite large and remember that in those days the bores were cut to tight tolerances. Anyway, I worked up a load by firing into my 'test tube' as I call it, until the patch was coming off at the muzzle. I then took that load out and tested it at 100 meters and I got a pretty decent grouping. With open sights it was something like 1.5 MOA. After a while, accuracy seemed to drop off and I found that the bore had smoothed up and the patch was no longer coming off properly so I increased the powder charge.
I would say that pressure and velocity are closely linked in that both translate into stress between the boolit and bore.
That pig gun I mentioned, I was shooting a 194 gr boolit over 44 grs of H4350 to produce 2040 fps from a 14.6 inch barrel! Pressure was right up there and yet no leading (accuracy not so great though). But once the bore got rough again with fresh corrosion, the patch would fail even with light loads. Same with the carbine even though it was only a light rust in the bore. I wonder about certain primers being corrosive?