Re: Any ideas why my 1-8 twist 6.5mm barrel refuses to shoot 142\'s well
Without more info it is hard to tell. Is it tight neck, what brass, seating in or off lands, moly etc?
As a general rule sierras shoot best just kissing lands or little off. The custom vlds such as berger, jlk, cartaruchi like to be into the lands as much as .025.
Never could get sierra 142s in moly to shoot consistent in my 6.5/06AI. Went back to plain and tightened right up.
Could be brass problem also. If you are not neck turning and using remington brass especially.
Try using the Audette or ladder method of load development with one bullet and powder and find the barrels sweet spot and fine tune from there. I normally leave sierras about .010 in for that test and once find powder load work it back out. With the VLDs, I jam seat, measure the mark, and seat at half that distance and shoot ladder and come back on seating later. Leaving long for test means you only have one way to go to find best spot and that is back.
Mine with 142 will group from 5-8" consistent at 1000. Working with the 140 JLK and it seems to have better potential to come under 5". However the 142 has a bearing surface that is .112 longer than the JLK, that causes problems in enough neck for the jlk with my throat. Mine was originally throated for 142s which have a longer bearing surface than VLds.