You could try putting some axle grease, hand lotion, or what ever will have some decent weight or consistency to it, down the muzzle. Then use a brass or wooden dowel with a patch wrapped around it to create a seal, then pound it out with a mallet, it should pop right out. Nothing will defeat hydraulics.
Another option, find a bullet that is relatively smaller than the bore, wrap a patch, condom, or something that will as well create a seal, and then tap against it with a mallet, or the like, with the same as above hydraulic effect.
One or two sharp hits should pop it out.
GS