every ammo failure i have ever had has been factory. i have missed a big buck (boon and crocket size) due to a squib, in a box full off ####ed up shells that %70 wouldn't chamber (remington). Not to mention a few kabooms from federal ammo over the years. i dont trust factory ammo for important stuff anymore.
i gave never found a factory load that did better then 4 moa in my P14... but hand loading i got it shootibg about 1.5 . and at about $70 a box for.303 these days... for the cost of 40 factory rounds, i can still build about 150 reloading.
factory ammo has come a long way for projectiles... but the powder metering and brass QC is still crap for most of it.