I have a circa 1882 model '73 Winchester in .44 W.C.F. that has an oversized groove diameter of .433". I have found that an .06" thick polyethylene wad under a bullet as small as .427" t will seal the gas behind the bullet and allow the bullet to center in the barrel and give accurate shooting. These results are from using a load that generates less than 15,000 p.s.i. and a velocity of 1,300 f.p.s.
Since your bullet is closer to your bore diameter, I am betting that a .06" poly wad would keep the gas from getting by your bullet, providing that the chamber pressure was not great enough to get past the poly wad. If one wad does not work, try two. I am not familiar with Bridgers best .45 wads. Are they made from polyethylene?
You could also try sizing .45 caliber gas checks in your sizer die (preferably .458 - .459), then start them upside down in the case, then seat and crimp the bullet.
The light .45 bullet has less bearing surface length than it does diameter, which would lead to a rapid deterioration of accuracy as the velocity increases. A harder alloy such as Linotype or heat treated wheelweights would be of benefit. (Also, the bullet diameter would over .001" larger in linotype.)
As Marshall suggested, another option would be to size them down and paper patch them.
Another method to try is to put two thicknesses of aluminum foil between the mold halves, spacing them about .002" apart. This would make for a slightly out of round bullet which would be the proper diameter part way around. You might be surprised how they might work. Use a dipper or drop pour if you do this.
A final option would be to bump up the bullets.
Please let us know the results of your testing.
John