If they didnt chamber up you could trim a few cases back to the length that would and dedicate them to those bullets, or maybe just use 44Spl cases. Your choice of powder could be 'tuned' to get the velo you want, within spec, of course.
Or, forget the crimp groove; its a single shot; seat the bullet where you want and the case neck tension is going to hold it there (unless you can pull it out by hand). Single shot target shooters (you know, the guys that the score matters) rarely crimp.
As to anyone else's chamber measurements, they mean nothing as regards yours.