Check the hunting regulations in your state if you intend to hunt deer with it. Some states have restrictions on how short the barrel can be on a ML, and they may not allow you to use a barrel that Short.
The Maximum Efficient load of powder that barrel will shoot is ONLY 47 grains. So, Use 3Fg powder ONLY, and be sure to use BLACK POWDER only. That way you will get some velocity out of that short barrel with enough power to help the 180 grain RB penetrate a deer- sized animal.
If you don't know, that gun comes with a POWDER CHAMBER that is smaller in diameter than the .50 cal. Bore diameter. You will need a .22 or .30 cal. Bore Brush to get into it to clean it.
There is a tiny hole( My main objection to the gun, BTW) from the powder chamber at the breech of the barrel, into a FLASH CHANNEL, that is hardly much larger.( My other objection to this gun.) Powder has to fit down through this tiny hole to go into the flash channel, and then over to the Vent or Touch Hole( TH) For positive ignition. That is why I recommend using Only the smaller granular size, 3Fg powder. The larger sized 2Fg often will Not fit down through that tiny hole.
There are two cures: Use an end mill cutter to remove the powder chamber, or drill out the tiny hole to something a bit bigger. Then drill out that flash channel to make it bigger, too, and Polish the heck out of that channel. A smooth side, without chatter marks from the drill bit, will not allow CRUD to build up in that channel and block either the powder or the burning of powder, causing a misfire.
Get both a cleaning Jag, and a LOADING jag- like the cupped one that comes on your factory rod, along with a Stainless Steel, or brass, or Aircraft Aluminum RANGE ROD.
You also need:
A good vent hole pick;
A short starter;
Cotton Flannel cleaning patches- about 2 1/2 " square or round( HINT: Go to a fabric store and buy a couple of yards of flannel. Then cut your own square patches at home. Saves a lot of money.)
Patches to use around the RB you load into the barrel, that are thick enough to fill the grooves, and grab the ball securely so the fabric will transfer the spin of the rifling to the ball. For your .50, try .015- .018" Patches( muslin, Cotton, Linen- Pocket drill, and pillow ticking) With a .490" Diameter RB.
For target shooting at 25 yds, a load of 30-35 grains of 3FG should be enough to give you accuracy without much noise or recoil. For hunting, try 45 -50 grains of 3Fg. Zero the gun at 50 yards, and limit the yardage at which you will fire on large game, such as deer.
You should also have some way to pull a ball from the barrel- either a ball jag, which looks like a wood screw welded to a machine screw to fit the end of your RANGE ROD( which it is) or a CO2 ball discharger. Get a box to put your stuff in.
Buy a good Adjustable volume powder measure. I recommend buying a measure that has a funnel attached by a hinge to the top of the measure, to help get ALL the powder down the muzzle!
You can find pictures of all this stuff at Track of the Wolf, and in the on-line catalogs of many other suppliers. If you go up to MEMBER resources on the index page to this forum, and scroll down to "Articles, Charts, and Links", and click on " links", it will take you to a long list of suppliers. Click on the name there, and their websites will come up on your screen, with their catalog, if available.
If you use 3Fg powder for your main charge, you can also use that powder for priming the flash pan, instead of buying 4Fg powder.
Until you get some experience shooting the gun,you can load from the can or bottle of powder into your SEPARATE POWDER MEASURE. Later, you can invest in a powder HORN, and make a non-adjustable measure to fit your favorite load.
Best of wishes to you. :thumbsup: