There are hundreds (if not thousands) of articles & directions on how to get a Ruger #1 to shoot more accurately than it was as received.

I'd lay odds that overweight Winchester is more accurate than your lightweight #1 - maybe that's what they were thinking?

2 - 3 shot groups with cheap, run-of-the-mill ammunition is not a good indicator for judging the accuracy of a rifle that is broken in, let alone new. Break it in with all your ammo, cleaning every 5 shots or so, THEN try some good semi-custom .45/70 factory ammo and see how it shoots. You might even try the Hornady 325gr. stuff - still not semi-custom, but probably better than the RP or WW.

1st of all, the #1 was not a good choice for someone expecting bug hole groups from a big bore rifle. Typically, large bores can shoot, but you will probably need handloads to do it and in that rifle, maybe some 'work'.

Both my last .458's shot under an inch & a bit less (bolt guns). Both were wildcats, so needed handloaded ammo. Did every load shoot under an inch? No. That's the problem with handloads - you are stuck with what it does.

If you want to shoot weak ammo, try the 405gr. RP's. I'd about lay odds they will shoot into an inch and 1/2 or smaller. The same bullet handloaded to 1,800fps to 2,150fps, probably inch or better yet.