.375 ROUND BALL
Ball diameter should be no more then a thousandth of an inch bigger then the smallest diameter in the guns barrel. This is usually right at the muzzle on a choked gun. The minimum diameter for best accuracy can be calculated by the following formula: (Min. Ball Size) = (Min. Internal Barrel diameter) – (2 x (Wad Petal Thickness)) in other words when the wad is inside the barrel the ball does not rattle around inside the wad because it is too small. Normally standard wads have a petal thickness between 0.020″ & 0.035″ and non-toxic shot wads have a petal thickness between 0.035″ & 0.050″. The balls should be cast of an alloy harder then pure lead. Pure lead balls will turn into misshapen hunks of lead under the acceleration forces when the gun is fired. For best accuracy the ball must remain round. Minimum hardness for the balls to remain ball shaped is about 20:1 alloy and WW alloy, which is harder still, works great. Regardless of what size or alloy you make your balls you should always manually check them for safety by dropping one through the guns barrel from breach to muzzle. With a ball that is a thousandth bigger then the smallest point in the barrel, slight hand pressure with a wooden dowel may be needed to get the ball to pass fully through the guns barrel. If anymore then hand pressure is required to make the ball pass through the barrel it should not be used for that gun. This may seem to be a no-brainer test but it should always be done with smooth bore guns, it’s one of those “just to be absolutely sure” kind of things. With rifled guns considerably greater resistance is acceptable because the ball has to engrave the rifling.
Wads must be modified for pumpkin ball slug loads. This is accomplished by cutting down the petals of the wad to form a shallow cup which encloses only the bottom half of the ball. I call this a “ball cup wad” for the bigger balls within the acceptable size range the cup should enclose slightly less then the bottom half of the ball. For the smaller balls within the acceptable size range the cup should enclose slightly more then the bottom half of the ball. If you want exact measurements call it 7/16 and 9/16 of the balls diameter. This arrangement of holding half the ball will give the best accuracy. It will hold the ball dead centre in the barrel without allowing it to roll or bounce along the internal walls of the barrel and give a clean release from the wad once it leaves the muzzle. Additional gas seals or various card, felt, or cork wads are used under the ball cup wad in order to achieve the correct wad column height for a good crimp.
Shot Buffer both under, around, and on top of the ball improves accuracy. A fully buffered ball will ride more centred in the barrel, pass through the choke without bouncing of one side of the choke, and have a smoother separation from the ball cup wad once it leaves the barrel. For best results I recommend the use of BPI#47 buffer. This buffer unlike others is Teflon based and will not pack like other buffers. Packing raises pressures in a load. The #47 buffer may still raise pressures by a very slight amount but nothing like other buffers will do. It will take a little bit of experimentation to figure out exactly how much buffer to put in both under the ball and on top of it. The best way to measure buffer is with a set of Lee dippers. What you want to do is put just enough buffer inside the ball cup wad so that when you put the ball in next it fills up all the empty space under the ball around the edges formed by the curvature of the ball. This “nests” the ball providing an even soft thrust platform and prevents the ball cup wad from sticking to the ball and not separating cleanly. Figure out which of the dippers dumps in the right amount of buffer to accomplish this. If the correct amount falls in-between two dipper sizes use the larger one. Next you need just enough buffer on top of the ball to fill in around the edges and just cover the ball. Again, use the larger dipper if this amount is between two dipper sizes.
Powder Charge is calculated according to the combined weight of the balls, buffer, extra wad spacers, etc using equivalent shot load weights. A good deal of research has been done in this area by enterprising individuals and the general consensus is that when you use a single slug of identical weight to a shot charge with otherwise identical components and powder charge the resulting pressure will be if anything less then the equivalent shot weight. This is due to the fact that a mass of small balls acts like a fluid under acceleration and applies pressure sideways against the internal walls of the barrel thus increasing friction and thus the pressure of the load. The single mass slug does not do this — thus the lower pressure. With rifled barrel guns and full bore size slugs pressure reduction is minimal do to the additional friction from the rifling. It would be best to stick to linear burning curve powders such as those produced by Alliant but with single ball loads this is not a necessity like it is with multi-ball loads.
Hulls used can be whatever you prefer and what you can find equivalent shot weight data for.
Crimps can be either fold crimps or roll crimps provided you have properly buffered around the top of the ball. If you choose not to buffer around the top of the ball do not use a roll crimp. The reason for this is that without the buffer around the ball the over-shot card could get “over-run” by the ball thus resulting in a barrel constriction and potentially “explosive situation” I recommend sealing crimp joints with finger-nail polish to prevent leakage of the buffer during long term storage, transport, and handling, especially when rattling around in your bag on a hunting trip.
This Article is courtesy of http://www.buckandslug.co.uk/ and printed here by permission. Please visit Richards website for some great .410 info. from our friends in the UK.