I went to the range this morning with Nat (my eighteen year old) for a session of plinking with the .223 and the .308 both at 100 yards. The .223 behaved faultlessly and so did the .308 to start with then the POI shifted. For the first dozen rounds or so we were aiming at and hitting those one inch shoot and see dots then for no reason the POI moved about eight inches to the right of the POA, thinking it was a flyer the next two shots cloverleafed with the errant shot so obviously something has shifted. Checked the mounts and all were good so we rezeroed and all was good again for another dozen rounds or so then the POI jumped to the right of the POA by a couple of inches and it continued to hold the same POI. Rechecked the scope mounts and checked all the action mounts, everything is nice and tight. Re zeroed for the second time and everything is going perfectly then after a few more rounds the POI jumps to the right of the POA by another couple of inches.
If it was duff ammo i wouldn't expect the groups to stay tight which they did, it was just that they jumped to the right by a big margin. There was no detectable vertical shift and it wasn't a steady deterioration, it was sudden from one shot to the next and the POI didn't move from its new position.
Needless to say there was a lot of humming and hawing but other that loose action or mounts nobody had a suggestion of what might be the cause. Prior to today it has shot flawlessly and very accurately.
It is a .308 with a Barnard action shooting through a slow twist 30 inch heavy Lilja barrel, a jewel trigger (very light) all in a Dolphin chassis. The scope is Sightron SIII 8-32 with simple cross hair reticle and eighth MOA click.
Does anybody have any ideas what could be causing this before I give up and send it back to Dolphin to fix.