The Gauge System in Shotguns: This is a method of measurement of bore diameter based on the quantity of lead round balls of a certain size that would equal one pound in weight. For instance, a 12 gauge shotgun has a bore diameter of .729”, and 12 lead round balls of this diameter will weigh one pound. Thus, the smaller the number, the larger the bore diameter. The one exception is the 410 shotgun, which is the true bore size in thousandths rather than a gauge measurement.

Service Charges in Shotguns: The British service charges for breech loading smooth bore guns, as listed in W.W. Greener’s book, “The Gun and It’s Development” (9th edition, published 1910) is as follows:


Black Powder in Grains

Black Powder in Drams

Shot Charge




1 5/8oz.




1 1/4oz.




1 1/8oz.













One Dram equals 27.34 grains.

This may be used as a guideline for muzzle loading guns as well, although I recommend starting with a lighter load and working up. For instance, I use a 16 gauge load in a 12 gauge muzzle loader and find that it works very well, plus it is more pleasant to shoot. Outside of turkey or waterfowl hunting, it is not necessary to shoot full service charge. The standard British velocity with black powder was 1050 f.p.s. which was found to give the best patterns.

Loading through Choke Tubes: This is a problem that never existed in the muzzle loading era. Choke boring was not widely used until 1875, which was well into the breech loading era, where you did have to worry about getting down past the choke with the wads. After choke boring became available in breechloaders, some live pigeon shooters who wanted to continue using their muzzle loaders had their guns jug (or recess) choked. This consisted of reaming a recess into the bore that was larger than the bore diameter, about 6” long, starting back about an inch from the muzzle. The shot hit this area, expanded, and then forced the shot back down to original bore size, creating the same choking effect as our modern constriction style chokes. Now, some new muzzle loading shotguns have screw in chokes. This provides the choking effect, but loading down thru them becomes a problem. The difference is, that the wads used in the jug choke were matched for the bore size and going thru the recess was no problem. A full choke 12 gauge gun has a constriction of .040”, which makes the bore size at the muzzle a 14 gauge. Since the overpowder (nitro) card seals the powder gases, it has to be 12 gauge or the gas will blow by it and the load will not create sufficient pressure to shoot well. There are two possible solutions to this. First, load your gun before you screw in the choke tubes. This may work if you are hunting and don’t expect to fire too many rounds, or, second, place the nitro card on it’s edge and force it down thru the choke tube with a ball starter, then tip it over flat once you have gotten past the choke and seat it on the powder. This does the least amount of damage to the wad, by only flattening it on 2 sides. The fiber wad can be undersized, for instance, using a 14 gauge fiber in a 12 gauge full choke gun, as the fiber would be destroyed ramming it thru the choke. A 11ga. or 12ga. overshot card is thin and flexible enough to go thru a choke tube without damage.

How To Load a Muzzle Loading Shotgun

Remove oil, etc. by wiping out the bore(s) and snapping a few caps with the muzzle pointing down to ensure that no oil remains. Be sure that the nipples are tight or they may blow out. We strongly recommend hearing and eye protection at all times, along with shooting gloves.

1. Pour correct powder charge(s) into gun. We recommend powder charging using a powder dipper and dipping out of a covered container when possible. Allow a few moments between shots. There is always a risk that an ember from the previous shot is present in the barrel and could set off the new load at anytime during the initial loading sequence. If you were using a flask and this happened, you could be holding a bomb. By using a dipper and a covered container, only the amount in the dipper can go off. Do not blow down the barrel after a shot. This could excite any embers that may be present when you drop the next powder charge. In the field, pre-measured “speed loaders” will work . Always use black powder or black powder substitutes only! Never use smokeless powder.

2. Insert the 1/8” overpowder (nitro) card(s) of correct size and seat it firmly against the powder. This wad is the gas seal that creates the pressure needed for the correct load performance.

3. Insert a fiber cushion wad(s) and ram it down firmly against the nitro card. This wad acts as a shock absorber to prevent shot deformation. This wad can be lubricated.

4. Pour correct shot charge(s) into gun. Insert overshot card of correct size and ram it firmly against shot charge. You are now loaded. Do not cap or prime the gun until you are in the shooting station, or are in the field hunting.

Two more thoughts here. First, it is sometimes necessary to use one size larger overshot cards (i.e., 11 ga. in a 12 ga. gun) so the recoil of the first barrel does not cause the shot charge of the second barrel to move forward. You can tell if this is happening if your second barrel does not pattern well. We recommend this practice in all muzzle loading double guns. Remember, ALL components must be seated firmly, or you run the risk of creating a bore obstruction which could bulge or blow up the gun. Second, take the time to pattern your gun. You can sometimes tighten a pattern by cutting the fiber cushion wad in half thickness. Some guns will shoot well with a full wad, some like half of the wad. Also changing fiber wad material may change things... If you see a hole in the middle of the pattern, cut the fiber wad in half, it cuts down the tendency to blow the fiber wad up thru the shot charge, and will sometimes close the hole.

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