I too have a Win Mod 70 Featherweight that I purchased new in the late 80's (non controlled feed action). The best I have ever been able to get it to consistently shoot is about 1 1/4" and that is with certainly handloads. The skinny, lightweight barrel is really a roadblock to getting MOA accuracy.
However, if you are having trouble reaching at least 1 1/2" after all of the things you have already done, you might want to consider recrowning the barrel.
---------------The last reloading manual I have that lists Winchester 450LS powder is the Speer number 8 manual published 1970.
Yes, what powder are you using?
Reloading: looking for Winchester 30 caliber .308 dia. 150gr. silver tip bullets/quanity 1000.
Alliant's 2400 or Winchester's 296 are both good powders for the 32/20 and will cover bullet weights from 85 up to 135 grains
Rather than answer your question, I have posted a link to the Winchester reloading data below. I would strongly urge you NOT to ask for relaoding data on an open forum. Anyone can answer a question here- for all you know, I am 10 years old. (I'm not- but you have no way to verify that!) Link at the bottom of this answer- and shoot safe.
Reloading Manuals
Grains are a unit of weight. Bullets, powder charges and brass casings are all measured in grain weight. So, yes there are different grain weights in reloading. There are also different powder grains, as in the texture of the powder. Those include, stick powder, ball powder, flake powder, etc...
First, for your safety please DO NOT solicit reloading data from anonymous sources on the internet. In wikianswers- anyone can answer a question- for all you know, I am 12 years old, and Mom does not know I am on the computer (I'm not- but that is beside the point) Hornady does not recommend IMR 3031 for the 160 gr FTX bullet in 30-30. This is a link to the Hornady reloading page for your caliber. PLEASE do not use reload data except that which is published by a powder company, a bullet maker, or manufacturer of reloading equipment. Safe shooting to you= C3. supervisor
The reloading data depends on the powder being used and the bullet weight. Try doing a web search for 308 reloading data and you will find lots of useful information.
You will have to experiment to find out. Start with available reloading manuals
You have a Model 1885 Single Shot Rifle that was manufactured in late 1901 or early 1902. Factory loaded ammo was discontinued for this cartridge circa 1935. Reloading dies can be purhased from RCBS or CH4D, but they are expensive. The hardest part will be finding carrtidge cases.
One can buy RCBS, Hornady, and Dillon reloading dies from the Reloading Dies website. They also sell more and the categories inclue add-ons, gaming, hunting, and recreation.