This is an urgent enquiry. Has anyone got the answer to this problem. I have a stainless steel 6 groove 1 in 10 twist 6 inch barrel, fitted to a S&W 686.
Testing it out at 25 metres produced lousy groups - 3 to 4 inch was common. I used a variety of powders Bullseye, Viht310, GM3 and 231. (Viht 310 is slightly faster than Bullseye) The ubiquitous loads of 2.7 or 2.8 of Bullseye and Viht310 used with a very finely produced 148gr swaged HBWC, and the same with the other two powders. FPS ranged from 680 to 750 across all the rounds fired. The best group actually came from some solid wadcutters, hard cast and cheap as chips pushed around 850 FPS. It could cloverleaf 3 rounds, the other 3 spread individually. I did get some spitting from those. In the past I have shot a sub inch one hole group with these loads so this is a mystery to me.
One clue I have is that the barrel was crudely slugged previous to fitting (bullet hammered down a bit of the barrel) which measured .355. A bullet fired from the revolver was recovered from the backstop and although mushroomed nice and evenly at the head, the skirt again measured at .355. Although I cannot 100% rely on these measurements being that accurate, could this be the reason?
I am due to test it again this Friday but have only .356 158gr SWC and .356 125gr round nose - not the best for a PPC. Can anyone solve this mystery.