A while back I posted a message about poor grouping from a PPC barrel. I got several helpful replies suggesting remedies.
I put these into effect. Results were great - one hole groups at 25 metres. Yippee. But now I have leading problems around the forcing cone and a short way up the barrel, half inch or so. Leading occurs within 15/20 shots
I now have the same barrel which slugs at .355 and 1 in 10 twist. the forcing cone was cut 1 mm deeper than a Browns insert and still at 11 degree. The crown was recut to a recessed flat 90 degree about 3mm inside an 11 degree outer.
Loads used vary from 2.1 to 2.7 Viht 310: 2.7/2.8 Bullseye: 2.7 to 3.2 GM3
Bullets .355 to .358 HBWC with a hardness of around 9.
The one hole group was achieved with 2.7 Bullseye with a .355 smooth sided HBWC. I sat all six rounds inside a single black patch at 25 metres.
I read all sorts of reasons - too hard or too soft bullets; too fast or too slow; too big or too small diameter;
The leading occurred in my first batch of trials working up from 2.1 Viht (a fast powder above Bullseye but slower than Titegroup) using a .357 HBWC through 2.2; 2.3; 2.4 etc when I stated to get fliers and found the leading to be the culprit.