Arrange to ship powder to your Outfitter, or Guide, or someone where you intend to hunt, using UPS or some other shipping service. Obey the law. You will have enough problems with sniffers alerting to shoes, clothing, boots, bags, etc to even the HINT of BLACK POWDER residue that you should not expect to be able to send any kind of BP through commercial carriers.
I hate to be a prune about this, and I don't like the laws. But, the best advice any lawyer can give you is to OBEY THE LAW, or find some other means of getting to your hunting site. I know there are a couple of lawyers who also frequent this site, and we have all been quiet, hoping that common sense will prevail.
Mr. History's experience is REALITY, folks.
If I were flying and wanted to transport my MLer, it would be in a case- preferably a hard case-- with the cock removed, to disable the gun and make it much less attractive to thieves. I might also remove the frizzen, or the entire lock, to prevent it from being broken in shipping. I would put the cock and frizzen( or entire lock) in my luggage, along with my tools needed to reassemble the gun, and alert airport personnel at baggage check in that it is there. I would use pre-measured powder charges, or take a fixed powder measure, washed out and dried to remove even the odor of BP, to measure my charges on arrival at the hunting site.