One problem I see is there is no forearm screw escutcheon and the screw is compressing a ebony wedge and seems like it needs tightening all the time. I put an "O" Ring under it and I'll see if that stays and improves anything. I just need some good weather now to test it.
I shoot all my single-shot schuetzen rifles off the barrel and the forend on all of them has full contact. The two Borchardt-Niedner .25-Krags seem to shoot better off the forearm so that's what I've been doing. The other Borchardt with full forend contact has averaged .788" at 100-yards for 200 shots.
How about trying it with the forend removed? Or with a temporary forend? That forend 'attachment' sounds like a possible culprit to me.
Even though the barrel rest is less accurate with this rifle, would it be worth the effort to see if it still shoots erratically when resting at the muzzle?
I completely understand about not wanting to change enything, but that 'attachment' is mickey mouse for sure. I'm afraid it would stick in my craw to a certain degree.
Regards, Joe