About 30 years ago I did a lot of experimenting with bullet design and I feel I came up with a simple formula that fits the bill for hunting bullets of the cup and core type that worked quite well no mater what the bullet weight or diameter is.
The formula is as follows.
(#1
At any given diameter the ratio of jacket to core should be 50% of the diameter of the bullet. In other words a 30 caliber bullet should have 15 caliber worth of jacket and 15 caliber worth of lead. The jacket used as the cup when starting out is .075" thick strip. Therefore .075" X2 for the total of .150". (+ or - about 2% is fine) That means you have a .075 jacket formed into a cup.
That's far too thick to expand much. Yup....it is! That's the idea in fact.
So, step #2 is to measure the length of the ogive. Any Ogive. Now taper that from it's base thickness , (in this case .075") to .006" at the nose.
The taper is done with a swedging punch from the inside so the outside sill looks like a cylindrical cup, but the mouth is thin. A male/female die set is used for this, so the outside cannot become any larger. The taper is made from the point on the inside of the jacket that is even with where the shank and the ogive of the bullet depart. Next a core is swedged in, and the ogive formed. Putting a cannelure into the jacket at 33% from the base and another at 66% from the base makes "waists" inside the jacket that help hold the core, just like the old Remington Core-Lokts did, but 2 instead of one. There are not made for crimping the brass case, but only as locks for the core.
The thin nose will expand at fairly low impact velocities, down to about 1650 FPS but the heavy jacket keeps the bullet from breaking up even if heavy bone is hit, or impact velocities are high. This is not fool proof, but it works in the large majority of cases, If the bullet turns sideways and bends a bit it can still "squirt out" he core, but it does so on thinner jackets too, so that is not an argument against the design.
Bullets generally mushroom at the nose to about 50% larger then unfired size, so a 30 stops expanding at about 45 cal, a 22 expands to about 31 cal, a .375 stops at about 56 cal, and so on.
I did this with hand made bullets from 22 cal to 45 cal and found it was pretty universal no mater what diameter they bullets were and no mater what weight (length) I made them.
I believe this is the best formula to follow for cup and core bullets. But I can't seem to get any of the big boys to listen. Some of the older Remington Core-Lokts and a few of the WW Power Points were close however. So did some of the old Kynoch bullets from the 20s.
Production with factory available strip sold by Kennecott and Anaconda seems to be the factor.
The machines are all set to use it, so changing over to other thicknesses will cause problems (I am guessing anyway) plus the factories would have to make their own rolling mills to form the jacket strip for each caliber.
Anyway, just information from 30-35 years ago.
Interesting to some, but perhaps not relevant. I seriously doubt any bullet manufacturer is going to take it to heart.
Last edited by szihn; 07/02/18.
