I have a T/C Carbine in the 45-70.

Shooting anything but the lighter loads beats the heck out of me and I have a problem with vertical stringing of my groups as the loads get heavier.

Maybe I am just too old and can't maintain a consistent hold with this little rifle, but it is driving me nuts. I don't have this problem with a lot of other rifles that weight in the 8 to 10 pound range.

I am using the Lee 340gr. cast bullet sized to .460" diameter. I have tried trail boss and Unique powders, both starting at 10.0gr. and working up. I have no leading or fouling problems of any kind.

My 10.0 to 11.0 gr. loads with Trail Boss will group in the 1-1/2" size at 50 yards but as I increase the powder charges, the groups get larger and start to string out vertically. Testing by pointing the rifle straight up, "Powder to the rear", the groups were best. Rolling the cartridges on the bench and loading with powder in bottom of case in horizontal position, groups were much larger, up to three times larger.

This indicates the powder is far more position sensitive than data suggests.

I still think most of my problem is not being able to maintain a consistent shooting position and follow through with this really light rifle.

Any suggestions will be greatly appreciated.

The only thing I see going on here is that you are going from an accurate to inaccurate ones.

Vertical string is not uncommon with Encores and Contenders and can usually be traced to a pressure point on the fore stock. It usually easily fixed with a little sandpaper.