I have been toying with an idea to shoot cast bullets cheaply, and efficiently, which is a lot of the point of casting your own. The known fixes are:
* dacron to hold the powder to the back for reliable ignition.
* fast fluffy pistol powders, with dacron.
* inert filler such as cream of wheat to reduce chamber volume.
So: what if I use silicone pourable casting compound and a waxed dowel pin down the center of some dedicated brass to convert my 5cc 308 win cases to ~2 cc with a ~.25 hole to the primer hole clear and the case neck clear?
For reference, I can either use 23 grains of alliant 2495 with a 155 grain bullet to get 1500 fps, or 17 grains powder and 26 grains of filler, or 12 gr powder with a reduced volume case. So the reduced volume case saves me 48% on powder cost, or about 3 cents a shot. The round costs 10.5 cents each, and is quicker to build than using dacron or filler, but takes making the custom cases, which add about 15 cents per case. Cases are re-used many times, so this is a few cents per round. Other less expensive casting compounds may work, such as polyester resin, vulcanizing rubber, polysufide,or epoxy, or wax might work, but 2 part silicone would be my first guess.
I have searched at least 10 times trying to get pistol powders, nope. And they are expensive. Whats the point in using 9 grains of pistol powder that costs as much as 15 grains of something else? Loading dacron is slow, and still results in low efficiency burns, so you pay 50% more for your powder than you should. Filler, ie Cream of wheat is still not ideal because its so airy that pressure still stays low, it has weight which must be accelerated, wasting powder, but does nothing for bullet energy on target, and gets everywhere, in my barrel, on my crony, and on my shop floor.
Now, I like the idea of a rifle that can load a fast long distance round if I want, or an energetic round to penetrate elk or moose. But I want to be able to fire 10 cent quiet shots at targets or squirrels as well, preferably with the same gun.
I have designed for elastomers and adhesives for years, and was a machinery stress analysist so let's assume I get the engineering part right. If not.. I will fix it or shelve it. Also, I have been developing internal ballistic calculations which seem to be working fairly well, so I am close to having accurate predictive ability of burn rates, pressures and such. Assume I also know how to safely test by creeping up on a design limit using failsafe precautions during testing.
My real question is about usability of such custom cases, methods of marking and handling so they dont get mixed into standard cases, and what capabilities would be best made. See, a case that efficiently burns my 2495 and will fire a 120 grain bare base at 1500 fps will not be able to fire a gas checked round at 2200 fps. You couldnt get that much powder in there.
So, if I became interested in firing 180 grain bullets at 2200 fps, I would have to either use a standard case with any of the above methods, or make a different custom case. Would etching the case with the usable volume on the low stress area of the base make sense? Paint comes off during forming. Small filed notches on the extractor rim would be easy, but wouldnt indicate volume, that would have to be known or measured.
Who else is interested in having custom low volume cases for their favorite rifle?
It should be mentioned that not having any kind of packing creates its own problems with hot explosive gas attacking the rear driving bands of the bullet. Either a small amount of filler, a gas check, a paint coating on the bullet, or some other idea would be required to address this.
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Originally Posted by williamwaco
