Designing the 2-diameter paper patch bullet.

[Distant Thunder]

There are basically three types of paper patched bullets.

The first step in choosing a paper patched bullet is to gather all the necessary information about your rifle to help you in choosing the best paper patched bullet for your rifle. I believe the fit of the bullet to your rifle is very important to accuracy with paper patched bullets. There are three basic types of ppb, bore diameter, groove diameter, and 2-diameter.

   

The first type of ppb is the bore diameter. When talking about bore diameter ppb I am referring to a straight, smooth sided bullet that when patched will be just a little snug on the tops of the lands when pushed through the barrel. This type of ppb is best seated out as far as possible, I seat my bore diameter bullets in the cases only .080-.100". This shallow seating puts a maximum amount of the bullet snuggly resting on the lands of the barrel, in perfect alignment. They can be extremely accurate for that reason. Also, they don't have to transition from the case into the lead and then into the rifling like a grease groove bullet does. They are probably best used in tight chambers where the case ID closely matches the patched bullet diameter. They can be made to work in grease groove chambers by neck sizing the cases to the best fit. Sizing cases down for every loading may require annealing the cases often. There are advantages to not having to go through all that.

Shallow seating is important with bore diameter bullets for one very important reason, it will help minimize the bumping up of the undersize bullet base to the diameter of your fired case when the powder ignites only to have it get squeezed back down to land and groove diameter as it moves into the barrel. This expansion and then down sizing of the bullet is not best for accuracy. This happens with any bullet that is seated into the case very far, but can cause problems especially with ppb and is best avoided.

   

The second type is the groove diameter ppb. These are patched to or slightly over the groove diameter. They can be loaded and shot just like grease groove bullets in rifles chambered for GG. Unless the rifle has a freebore, a straight unrifled cylindrical section immediately in front the chamber that is usually groove diameter or slightly over, these bullets can take up a bit powder space. This isn't a problem with the long cases like the .45-110 and may actually be desirable, but in a .45-70 a 540 grain groove diameter ppb can eat up much needed room for powder.

I designed a groove diameter pp bullet for my .50-70 just recently and it shoots very well, but that rifle has a freebore .350" long and the bullet isn't in the case too far. I can still load 75 grains of 2F with very little compression. That thread is on this forum if you are interested.

   

The next type is the bullet that brings together the best of both of the other designs, the 2-diameter ppb. It is the design that I want to explain in this thread. This bullet is perhaps the best suited to grease groove chambers and can be use in rifles with freebore to allow for a shallow seating depth like bore diameter ppb.

As the name implies these bullet have two straight sided sections of different diameters. The forward one is bore diameter when patched, the base section is groove diameter or .001-.002" over when patched. This larger base is made to be a much closer fit in the fire cases of a gg chamber and thereby eliminate the need for neck sizing and annealing for each loading. It can also reduce case growth and the resulting trimming of your cases so often.

With the 2-diameter ppb the length of the groove diameter base is designed so the seating depth is shallow like the bore diameter ppb putting most of the bullet up in the barrel for best alignment and increasing powder capacity. This gives a .45-70 almost the same powder capacity as a .45-90 and turns a .40-65 into a real .40-72!

I use a 2-diameter ppb in my .40-65 with 72.0 grains of 1 1/2 Swiss and only about 1/16" compression. It has proven to be very, very accurate and now handles the rams quite well thanks to the added velocity.

I happen to be just starting the design of a 2-diameter ppb for a .45-100 for another shooter. I plan to explain how I go about designing a 2-diameter ppb for a specific rifle so anyone interested in trying this design in their gg rifle can see the way I do it and what's involved. You should be able to follow the steps I use to gather the important information needed to have a ppb mold made that will give you the best chance of success.

DT