A precondition for good accuracy with minié bullets are properly dimensioned bullets that fit the barrel. Many .58 calibre bullet moulds have a .575" diameter, while the bore diameter of many muskets is .580 or more. Bullet moulds also have a tendency to cast smaller bullets than specified on the mould. Be aware that muskets that have progressive depth rifling may shoot better with under dimensioned bullets compared to muskets with ordinary rifling.

In my opinion the ideal when shooting minié balls is to have a bullet diameter that is about .001"-.002" less than the bore diameter. Actually, a bullet that measures the same as the bore diameter often works well, but you must make sure to have a good bullet lubricant that can keep the fouling soft when using such tight fitting bullets. Otherwise it may be difficult to load after a couple of shots.

You don't have to have custom bullet moulds made to fit your musket. If you have an undersize bullet mould they can be enlarged quite easily. You don't need sophisticated tools either. Note that the following applies to steel and brass moulds. I'm uncertain whether it is possible to enlarge an aluminium mould. You need the following equipment to enlarge a mould:

• A hand drill
• Fine grit valve grinding compound
• Brass or steel wood screws
• A file
• 4-5 perfect minié balls cast from the mould you are going to enlarge
• A vernier calliper or micrometer

Before you start

There are basically two ways to find out whether your bullet has correct diameter: with or without micrometer/calliper. I recommend using the micrometer/calliper method, but if you don't have any you can use the other method.

With a micrometer or vernier calliper

Slug the barrel of the musket that shoots the bullet from the bullet mould you plan to enlarge. When you slug it you must remove the breech plug, which is a job for the advanced. When the breech plug is removed you force an oversize lead slug through the barrel. Force the slug from the breech towards the muzzle. When the slug exits the muzzle it has a perfect print of the rifling. Use your measuring tool to measure the bore diameter (diameter across the flats). Remember, that on a slug the bore diameter is the smallest diameter and the larges diameter is the rifling depth. If your musket is .58 calibre you will probably find that the diameter is about .58". Afterwards you measure the diameter of the bullet you are going to shoot. If the diameter is below .578" in a .580" barrel it may be smart to enlarge the bullet mould slightly.

Without micrometer or calliper

Take a perfect cast bullet and insert it into the muzzle of the weapon you are shooting. The weapon should be wiped clean and free of oil. Insert the entire bearing surface of the bullet into the muzzle and wiggle it a bit. Does it feel loose? If it does feel loose you should enlarge it. I really recommend that you use the first method as this is more accurate. With some sort of measuring device it is easier to avoid enlarging the bullet too much.

Enlarging the bullet mould

Cast 10-15 perfect bullets from the mould. It may be smart to use a hard alloy. Wheel weights work ok. Make sure the lead fills out the mould properly. There should be no wrinkles or other defects on the bullets. While you wait for the mould and lead to heat you can find 4-5 wood screws made of brass or steel. Use a file to grind off the heads of the screws, but make sure that you keep the notch in the end (this is why you cannot cut the heads off with a hacksaw). Screw the modified wood screws into the bases of the bullets you have cast. See the illustrations below. Continue by securing the screw into the chucks of a hand drill.

'Lubricate' the bullet with grinding compound. Use the finest grit you can find. Insert the bullet into the mould and grab a good hold of the mould handles with your left hand. Hold the drill in your right hand and start it up carefully. Stop once in a while to add more grinding compound to the bullet. When the bullet is worn you have to replace it with a new. The honing process may take some time, depending on how much you want to enlarge your mould. To check how far you have come, clean the mould, and cast a couple of new bullets and then measure the bullet. The bullets must be cast as perfect as possible to give you a realistic impression. If the bullet still is too small you should continue the process. Keep it going until you have a bullet that is perfect for your rifle or musket. Be aware that it may take a while to clean a mould after it has been honed. Alcohol based cleaners or degreaser usually do the job.