50/70 questions

[Dave951]

I’ve been working on getting a 12.7 Swede to shoot. It has been rechambered to 50/70 and the bore is in very good condition. Slugged, rifling measures 495/515. Twist is 1/42. Brass has been fire-formed to the chamber. So far, the best I’ve been able to get is about 4in at 50yd. For an 8 shot group, 3-4 shots will be almost in one hole with the rest on walkabout.

So this is just to open a conversation on getting this rifle to shoot. I’ve worked through a number of combinations but I’m wondering if I’m missing a variable unique to the 12.7