@ 09:35 am (GMT)
Nathan FosterHi Jason, when I was young, I had folk (salesmen) tell me that ADI was just a cheap powder made in Oz, conjuring images of an Australian in a hut somewhere in the outback, making powder while trying to split the beer atom. Fortunately I was able to get past all of this and see the faults in my own processes. ADI make good powder, its as simple as that. So lets put that to rest.
Trying to diagnose this via the net is hopeless. I will try to offer some ideas but without having the rifle in hand, you can treat my comments as being as helpful as any other 'bullshit' you have been fed. Regardless, here we go:
To begin with, you must go back to 100 yards and report on groups.
If groups are poor at 100 yards then we might consider the following (assuming all steps in the books were followed):
Sand has blown into the muzzle after shooting on a windy dusty day (personally been through this once). Remedy- rebarrel.
Slow burn caused a secondary pressure wave at 3/4 barrel mark which has by fluke, created a minute bulge towards end of barrel. I have seen this also once or twice but could not put it into words until I saw external pressure test research from other sources after which the penny dropped. If this is occurs, it is reflective of the burn rate, but to this I would add bore dimensions and bore finish as relevant factors following my own research. There is more to this than the actual brand of powder. It is foremost an issue concerning a large but slow powder charge versus a small and long oriface. If the muzzle has a thin thread on it for a brake, this could also have swollen. If the barrel has bulged and there are no obvious signs of where it has bulged, it may have to be thrown away.
A basic change in the sweet spot node with throat wear (becomes apparent at 250 rounds in the RUM). Remedy- Polish throat and possibly increase charge by .5gr when retesting.
Scope or mounts loosened under ongoing recoil.
Please note that in some instances, when groups have suddenly opened up on me over the years via some internal bore change including wear, I have at times overcome accuracy issues by changing bullet weights, utilizing the longest pill I can find. The long bearing surface and drop in velocity can at times overcome internal bore issues. You may want to try the 225gr ELD-M before giving up on this barrel.
So there you go, thats some expert bullshit for you. Hope it helps.