- May 13, 2018 at 1:58 pm #50433kensParticipant
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what is the BC of this bullet?
I am building a front stuffer, and I reamed out a Lee 160gr spire point mold into a 180gr slick for paper patch.
How do I figure BC assuming a black powder muzzle speed of 1300fps?
What would be my best zero yardage to hit the gong at 300 & 500 yards?
- May 15, 2018 at 11:08 am #50457Larry GibsonParticipant
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Hard to say really but I’d bet an actual measured BC will be .3 to .325. A lot will depend on the amount of pitch and yaw on launch/discarding of the PP and the amount of engraving caused by the rifling.
- May 15, 2018 at 4:33 pm #50461kensParticipant
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it is a shallow groove barrel, .32/40 to be exact. I got a 1″ straight octagon 32/40 blank x 36″ long. I had it breeched to an Allan Foundry Underhammer action. it is .314/.321 and 1:14
BTW, I read an interesting article the other day. it was an article about the BPCR (black powder cartridge rifle) long range guys discussing a test of bullet shapes that fly well downrange,,,,,,, 600, 800, 1000 yards downrange.
The study was one bullet deep grease grooves spire point like a DEEP grooved Loverin, the other was a round nose with few shallow grooves aft in the body. otherwise all the same
The RN shallow grooves aft flew better than the spire point’s deep grooves forward, so they said.
The consensus of the article was to have few shallow grooves aft with the smallest meplat.
That describes the XCB, does it not? I thought that ironic.
- May 24, 2018 at 6:14 pm #50692GoodsteelKeymaster
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Kens, it does indeed describe the XCB. Reality is a two edged sword.
On the one hand, there is only one truth. Only one reality. Only one science. There are varying ways of looking at that one truth, but they better stay grounded in it, or they wind up spewing garbage that isn’t real.
On the other hand, there is nothing new under the sun. Hardly any way to improve on what is already known.
There is one exception to the status quo, and that is that people are not rational creatures but rationalizing creatures. Often we know exactly what to do, but constantly fail to put it all together into a coherent method. This is what I saw in the cast bullet world. I can’t tell you how many bullet designs there are out there that look real pretty but throw the reality of cast bullet shooting right out the window. Seeing these designs, you might ask yourself “what in the world was dude thinking????”. The simple answer is “He wasn’t.” He didn’t think that particular design would work, he felt like it looked awesome enough to be awesome and it just doesn’t work that way.
The XCB project was the desire of several experienced shooters, and one gunsmith (your humble servant) who came together with a common goal: To simply DO what we knew to do, and that which we knew was valid, and do it all at the same time, pointed the same way. Larry was instrumental in this objective as was BjornB, Sgt.Mike, Lovelife, and many many others, but Larry had the equipment to keep us grounded in reality, and he and BjornB set us a stalwart example of what to do and how to do it when devising tests to that end.
At the end of the day, it was the simplest thing in the world, but very difficult to accomplish (in no small part by the constant barrage of insults from those who would rather eat broken glass than follow a logical and transparent method). Larry and I (possibly more Larry than I) designed the XCB bullet to be simply right. Larry had come up with the idea of shortening the 30-06 case, which I improved upon by designing a reamer specifically suited to the job. That’s how the XCB bullet and cartridge came about. It wasn’t anything wild and crazy. It was all about giving the cast bullet a comfy way to have a real good chance of surviving the trip down the barrel. As you say, the specific principles had been discovered long ago, but no one had ever put them together with an entire system geared towards the same goal. That’s what made the XCB project special, and what determined what caught the name XCB and what didn’t. For instance, the 30XCB cartridge was simply Larrys 30X57 optimized in my shop for the project. In no way would I say we broke new ground with equipment. The XCB project was about method and an absolute refusal to compromise unless it resulted in faster speeds with more precision.
So you will find many of the same methods and “MO” in many different areas of the shooting sports. Everything from bullet design, to cartridge construction, to loading technique. The XCB is awesome not because it exists on the fringe, but because its smack dab in the middle of the spectrum with plenty of room to stay there. Any rifle you are looking to get precision out of (cast bullet or otherwise) would benefit from following the same methods.
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