In the mid to late 90's, I was fortunate enough to take a Machine Tool Technology Class at the local Community College. I took it over and over, with no interest in grades, course credits or graduating. As far as I was concerned, I was renting $1M worth of machinery, plus the expertise of the teacher, plus the experiences and mistakes of my fellow students, for a pretty nominal fee per semester. The instructor was totally sympathetic to my hobby interests, and kept what I was working on away from the myopic gaze of the Administration. My fellow students minded their own business as well.
There was a considerable line for the two Bridgeport clones in the Class, but the Horizontal Mill was largely neglected. I delightedly hogged this, plus the dividing head, for weeks on end without annoying anybody. One of the things I decided to try was to make a boolit mould. At that time, I had digested all the current progress on the Black Powder Cartridge section of the old Shooter's Forum, and by its help, triumphantly registered my first 2-1/2" 100-yard group using black powder in my old High Wall .45-70. So I thought I would try to make a boolit mould for the cartridge.
The big advantage of making one's own mould is that one can embody one's own ideas. First, it would be a nose-pour adjustable mould, like the old Perfection designs. That way, I would get the equivalent of many different length moulds from the effort of making only one. Dr. Gunn and Dan Theodore and their ideas were well in the future still, so the nose was more or less standard, with the necessary meplat.
I figured thusly: The depth of the grooves would more or less copy the nominal bore diameter, with a little extra depth for a film of boolit lube. The groove diameter would be, hopefully, at least the groove diameter of the barrel. The numbers were picked off the aforementioned Winchester High Wall, approximately 0.450-" and 0.457+" respectively.
I had made up some ACME threading tooling to make some replacement screws and nuts for my Atlas Shaper, and thought the ACME form might be a good one for the lube grooves. The idea was that the ACME form takes up and equalizes thrusts, offering increasing resistance from top to root as the thread form gets thicker in cross section, making the action of grip nuts on leade screws accurate over a long wear life. This configuration, I thought, would also help center the boolit in the barrel, as any off-center delivery would squeeze down the narrow, more fragile, tops of the ACME thread form against the more resistant, wider bottoms at the opposite side, and thrust the boolit to a centered equilibrium. I figured the boolit would also come out of the mould easier than with the square cornered lube grooves featured on a lot of the classic designs. Since the grooves were going to be only a few thousandths deep, there would need to be many of them to deliver adequate lubrication, like the Loverin designs do.
So, in the class, I turned a cherry to what I guessed would cut the correct diameter cavity to deliver the correctly sized boolit, cut the grooves with my ACME thread tool (I wound up cutting them deeper than planned just because they looked too tiny) and fluted it using the dividing head on the horizontal mill. I hardened and tempered it and ground the reliefs with a toolpost grinder on the lathe, and did the final sharpening with stones and diamond files. I made a little double-acting vise to fit Ideal single cavity mould blocks and recherried a set of junk blocks I had gotten cheap at a Gun Show.
The mould turned out pretty good (I thought) and I fitted it with a dished-base plate and an adjustment screw. The first few casts showed the mould was a few thousandths too small, so I lapped it out to what was a barely adequate size. I set the cavity to around 390 grains and tested it with the High Wall against the previously successful load which had used Ideal 457124. Alas, the Ideal design, at 100 yards, outdid my ACME boolit by at least 1/2 MOA every time. Turning off the base cavity to a flat base didn't help. I relegated the mould to the category of Col. Patterson's lion trap ("In point of fact, it didn't work, but it was a very good idea anyway") and went on to other things.
Recently, I dug the old mould out from my rather excessive accumulation of such things, and it occurred to me that I had never changed the adjustment for length. In the intervening decade plus, the value of longer boolits for better targets at longer ranges had become settled science. Also, I now had a couple of dedicated target rifles in .45-70, with pristine barrels. I turned the adjustment screw on the mould all the way out, which resulted in a boolit of around 532 grains, lubed a bunch of them up, and loaded them with a powder charge that had worked well with the 525-gr Ideal 457125. I took a few loads with this boolit out for comparison.
When I got to the range, I realized that I had forgotten my telescope sight, and the Shiloh #3 had no tang and globe. So I figured I'd use the barrel sights at 100 yards. The results are below:
The control load with the 457125 clone gave a 7/8" vertical by 1-7/8" horizontal 5-shot group. The ACME boolits gave three groups, 2-1/2" vertical by 2" horizontal, 3-3/8" vertical by 1-1/2" horizontal, with 4 of 5 in 2" vertical, and the one in the picture, 7/8" vertical by 1-1/2" horizontal.
Looks like I'll be checking the ACME boolit out at longer ranges in the future. And remembering my telescope sight next time.
Here's a photo of the mould, cherry and a couple boolits:
All in all, it was very instructional, and pretty interesting work. The hardest part seems to be figuring out the difference between the cherry dimensions and those of the boolit you want out of the mould, and the finicky hand work needed in deburring and honing the cherry's cutting surfaces.
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Originally Posted by Bent Ramrod
