If you spend a lot of time on line, you realise that once someone with some expertise writes something for the first time, all the search engines pick it up for eternity. The next thing that happens, is that whenever the question is asked again, the original reference is cited again and again, and it is very rare that the original information is validated. Sometimes, the information is correct, and other times it isn't, but the number of replications just continue to validate it, even if it is wrong. People cite it on forums as the gospel truth.
What got me thinking about this, was the other day I was looking for some info on lapping a barrel by firing bullets coated with various grades of grit lapping compound starting at about 220 and working through to 600-800 to polish. Apparently high quality barrels come already polished, but poor quality barrels can be rough inside, and thus foul quickly and heavily, which affects accuracy.
Somewhere on a forum, someone warned about using diamond grit as a lapping compound, instead of aluminum oxide or silicon carbide. And this has been repeated time again, saying that the diamonds stick to the barrel and damage it?
Now if I apply a logical mind, copper is softer than steel, which is softer than all three types of abrasive. If you roll a bullet in abrasive against a hard surface, it will stick to the copper. If you fire said bullet down a barrel, the abrasive will embed itself deeper into the copper than the barrel because it is softer. Once embedded in copper, it will still be able to remove material from the barrel because it is harder than steel, and smooth any rough tool marks within the barrel. I don't get how diamond paste can be worse than the other materials, as based on the hardness of the metals, it should always stick to the softer copper.
Nobody explains it properly (if there is a difference). The only thing I can think of is that the commercial kits are made of silicon carbide, whereas you can find diamond based polished in any grit size fairly easily on the internet and it is often cheaper. I wonder whether it boils down to manufacturers using the internet
and forums to protect their product?
For interest sake, diamond is a 10 on a Mohs hardness scale, aluminum oxide or silicon carbide are 9's and glass by comparison is a 5. On a different hardness scale diamonds are 9000 HrV, silicon carbide 2800HrV and aluminum oxide 1800 HrV. Diamonds are the most durable, silicon carbide is brittle and doesn't last long, and aluminum oxide apparently is not as sharp as the others. Perhaps there is an engineer here that can explain the significance of the above measurements in relation to lapping barrels?