When I bought cases for my 45/90 Sharps, the rifle had not arrived yet. I did not know the actual depth of my newly-cut chamber, but I decided to 'square up the mouths' on the new brass to make sure it was uniform.
Using my reliable old Pacific trimmer, I made gradually deeper cuts on a randomly selected case until the cutter barely 'shined' the full circle of the mouth. That case measured 2.395", which seemed perfect for a 2.4" cartridge.
With that setting locked in, I 'squared up' all 250 cases.
Boy! Was that ever a mistake!
For one thing, the trimmer did not cut a square mouth. A measurement of 2.395" could decrease to 2.390" by just turning the case 90 degrees and taking the measurement again. I didn't discover this until later, and it was never apparent on the small diameter case necks I had trimmed over the past thirty years.
The next thing to bite me was the fact that BPCR cases get shorter when fired.
Yep, unless you are using heavy neck tension, the case doesn't get longer...it just gets fatter. But, since brass is being 'moved' a fatter diameter means the length decreases.
Yes...you can recover the length with full-length resizing, but my best loads come from fire-formed cases.
That means a case which started at 2.390 (on the 'short side' of the mouth) gets down to 2.383". That, coupled with the fact that my chamber is actually 2.410" deep, leaves a gap between the case mouth and the chamber end of 27 thousandths...big enough to drive a truck through.
I actually became aware of the mismatch, and it's importance, when trying to determine why so much lead collected in the chamber throat.
Well, I bought a Wilson trimmer to cure the squareness problem, but certainly couldn't use it on cases that were already too short. I needed a way to make 'em longer, first.
It is well known that 45/70 brass can be redrawn to 45/90 length. So I started looking for information about that process. Eventually turned up 'basic information' by buying Nonte's book on cartridge conversions. All of the pertinent information was contained in a simple line drawing of a die and punch, with some vague suggestions about shaping and hardening. But the information was clear enough to make some guesses about 'dimensions' which would draw out a case by .030"...instead of .300".
Being 'latheless' I had no hope of duplicating the tools described, and I have no way to harden steel. I 'talked' with an 'internet aquaintence' who would make a set for me, but dropped me like a hot rock when (at his request) I offered an amount which seemed fair to me. Seems $75 wasn't even worth discussing.
So I needed a more 'ready made' solution...and hopefully one that was more 'affordable' than kicking out another $170 for new brass.
I seem to have found it.
Nonte's 'die' was shaped in a way that had all of the 'work' happening in the bottom half-inch of the tool. So it seemed to me that everything above that point was serving no purpose, except as a 'guide' for the punch as it moved downward.
Although I have never seen one, I learned that a common drill jig bushing with an ID of .500" is a suitable substitute for that bottom half-inch of the die. McMaster-Carr has a good selection of bushings...and they don't cost much. They are already hardened, polished , and radiused on the top corner of the hole.
All I needed was a hardned punch of suitable diameter.
Nonte's punch had a diameter of .480". That was needed to draw enough material for the .300" stretch. It works the entire length of the case wall.
For .030", a smaller diameter would cause only the brass just above the head to be 'rearranged'. As the case/punch moves deeper into the restriction, the case wall between the 'die' and the punch becomes thinner, and no more brass flow is generated. I tried several, but the 'smaller punch diameter' that works well is .468"
McMaster-Carr sells a 15/32" drill blank that works perfectly after the nose has been shaped to fit the brand of brass you wish to modify. Actually, the shape of the nose is critical. Before I got THAT right, I was quite adept at destroying cases.
Below are some drawings. One shows dimensions suitable for Bell and RP brass. Might work for Starline, but I suspect the nose would have to be lengthened some. Might work on W/W if the nose was shorter, but diameter may simply be too small for that thin-walled brass.
The other drawing shows the relationship between the case and 'tools'. The (green) die is a two-diameter drill jig bushing, but a single diameter bushing would be better. I bought one with a 'lip', but didn't need it.
The (red) outline on the case shows where brass is 'stolen' from to lengthen the case.
CM
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Originally Posted by Jon K
