What make of conicals are you using?
This is a common problem when cap and ball shooters use lead bullets designed for the .45 ACP or .45 Long Colt. Not only are they smaller than useful for the Ruger, but they lack a heel to start them straight in the chamber.
Or, you may have picked up conicals made for non-Ruger cap and ball revolvers. The Ruger requires a .457 ball, and a commensurately larger conical bullet, to ensure it stays in the chamber during recoil. Other .44 cap and ball revolvers fare better with .454 balls and conicals.
Tacklebury is right: you can squeeze the bullet a bit in a vice, but if it has a heel (a reduced step on the base, smaller than the chamber) you may also increase the heel diameter to where it's too big to enter the chamber and becomes useless.
Not sure where you can buy conicals for that Ruger. The Lee conical bullet, made especially for the Ruger, is not commercially available as far as I know. Those that use it cast their own, or get them from a buddy.
Lee makes two versions of the same cap and ball .44 mould. One bullet weighs 200 grains and is designed for most revolvers. The other version weighs 220 grains and is made slightly larger in diameter for the Ruger.
Pick up a Dixie Gun Works catalog and you'll find a large assortment of conical bullets in there that are not listed online. You may find a conical that is sufficiently large diameter. If not, you may have to cast your own with a Lee mould.
The Lee bullet, in either diameter, has a reputation for very good accuracy. Of all the conical bullets I've tried in the past 40 years or so, it remains my most accurate. But that's only for the .44 caliber Lee. I've not found the .36 caliber Lee design particularly accurate, delivering 4 to 5-inch groups at 25 yards from a benchrest.
The Lee .44 caliber bullet in my revolvers will consistently deliver at least 2" groups, and often smaller in certain revolvers. My Uberti-made Remington .44 is particularly accurate with the Lee 200 grain bullet, putting all 6 bullets into a 2" circle at 25 yards, from a benchrest.
But I don't shoot conicals often. Balls are equally accurate and far easier to find or procure. I put holes in paper or tin cans and don't need the increased energy of a conical for that task.
If anyone knows of a store-boughten source for Lee conicals, chime in. I've yet to find one. I hope the above helps.